S299: Enhancing Production and Reproductive Performance of Heat-Stressed Dairy Cattle

(Multistate Research Project)

Status: Inactive/Terminating

Project Menu

SAES-422 Reports

Annual/Termination Reports:

[03/28/2001] [03/25/2002] [03/31/2003] [05/25/2004]

Date of Annual Report: 03/28/2001

Report Information

Annual Meeting Dates: 01/27/2001 - 01/28/2001
Period the Report Covers: 10/01/2000 - 12/01/2000

Participants

John K. Bernard
Georgia
jbernard@tifton.cpes.peachnet.edu;

Nancy Cox
Mississippi
nmc1@ra.msstate.edu;

Keith Cummins
Auburn
kcummins@acesag.auburn.edu;

Lane Ely
Georgia
laneely@arches.uga.edu;

Robert W. Godfrey
Virgin Islands
rgodfre@mail.uvi.edu;

Brinton A. Hopkins
North Carolina
Brinton_Hopkins@ncsu.edu;

Charles Kadzere
North Carolina
kadzere@agnus.ag.ncat.edu;

Terry Kiser
Mississippi
tkiser@ads.msstate.edu;

David Morrison
Louisiana
dmorrison@agctr.lsu.edu;

Terry Smith
Mississippi
TRSmith@ads.msstate.edu;

Jerry D. Ward
Louisiana
jward@agctr.lsu.edu;

Steven P. Washburn
North Carolina
steve_washburn@ncsu.edu;

Joe West
Georgia
jwest@tifton.cpes.peachnet.edu;

C. Scott Whisnant
North Carolina
Scott.Whisnant@unity.ncsu.edu;

Lon Whitlow
North Carolina
Lon_Whitlow@ncsu.edu;

Scott Willard
Mississippi
swillard@ads.msstate.edu;

Project Leadership:

Chair: John K. Bernard, GA, jbernard@tifton.cpes.peachnet.edu

Chair-elect: Scott Whisnant, NC, Scott.Whisnant@unity.ncsu.edu

Secretary: Scott Willard, MS, swillard@ads.msstate.edu

Brief Summary of Minutes

The first annual meeting of the S-299 Multistate Project Technical Committee was held on January 27 and 28, 2001 in Fort Worth, TX. Twelve project scientists representing six states and seven institutions attended. After introductions of participants and guest, David Morrison, Administrative Advisor, spoke briefly about the opportunities available to participants through the IFAFS program. Chairman Bernard commented on the new NRC=s dairy guidelines and the need for additional information related to the nutrient requirements of heat-stressed dairy cattle. The duties of the officers were reviewed and a nominating committee consisting of Lon Whitlow (NC), Bob Godfrey (USVI) and Jerry Ward (LA) was appointed to submit names for the office of Secretary.

During progress reports, discussion focused on how to deal with current preliminary data, planning phases of experiments as outlined in the project proposal, and coordination of these activities in the coming year. Several participants were appointed as lead investigators in coordinating the development of experimental protocols for replicated projects. These individuals would draft a protocol for each sub-objective and distribute to the group for review. After revisions were incorporated, these protocols would be used by each station t collect samples and data for specific sub-objectives. The protocols should be submitted to the list-serve no later than March 1.

In other business, Bob Godfrey (USVI) agreed to coordinate and oversee the development of a web page for S-299. The address for the web site is http://rps.uvi.edu/S299/S299_home_page.html. The groups decided to hold the next annual meeting in conjunction with the Southern Section ASAS/ADSA meeting in Orlando, FL in 2002. Joe West (GA) was elected secretary for the coming year. Dr. Morrison expressed appreciation to John Bernard for pulling the S-299 project proposal together and for serving as Chairman of the first annual meeting. No additional business was brought before the group and the meeting was adjourned.

Accomplishments

Objective 1. To further elucidate direct and indirect effects of chronic heat stress in a hot humid climate on nutrient intake and metabolism, endocrine status, and reproductive and lactational performance of dairy cattle. 1a. Effect of environmental stressors on body temperature, nutrient intake, and performance Thirty lactating cows with shade but no cooling were used to determine the effects of environmental conditions on body temperature, intake, and milk yield (GA). The study was conducted from April 28 through July 21 when weather conditions typically change from warm to very hot and humid. There was a linear decline for milk yield across time which was much greater than the normal decline with advancing lactation. As temperature-humidity index (THI) increased, body temperature increased in a curvilinear fashion whereas dry matter intake (DMI) and milk yield declined in a curvilinear fashion. Instantaneous slopes revealed that at THI of 72, milk yield declined at a rate of 0.221, 0.911, and 0.575 kg/unit increase in THI for Holsteins when regressed on maximum, minimum, or mean THI, respectively. Jerseys were more heat tolerant than Holsteins. The endocrine and metabolic profile of heat-stressed cattle from the transition period to next pregnancy will be monitored weekly beginning 90 days prepartum and continued until confirmed pregnant or 120 days postpartum (NC). 1b. Effect of climate pre- and postpartum on intake and performance Studies to determine the effect of climate during the prepartum period on intake and performance postpartum will be initiated this year (GA). 1c. Effect of environmental stressors on reproductive performance The potential of supplemental cooling on sperm production of heat tolerant and intolerant breeds will be tested (USVI). 1d. Effect of genetic selection on heat tolerance or intolerance A model which incorporates information from public weather stations was developed to test for the effects of heat stress on production (GA). Maximum daily air temperature and minimum daily humidity were the most critical variables to quantify heat stress when the THI is above 72. Using DHI records from 134 Georgia dairy farms, the genetic correlation between general production and heat stress is around -0.3 (GA). This implies that continual selection for production while ignoring heat-tolerance results in decreasing heat tolerance. 1e. Effect of heat stress and production level on endocrine profiles Experimental protocols for collaborating stations are being developed (AL) for the coming year. Objective 2. To develop physiological, nutritional and environmental strategies to enhance milk production, reproductive performance, profitability and heat tolerance of dairy cattle in a hot, humid climate. 2a. Effect of nutritional strategies to enhance intake and efficiency of nutrient utilization and improve reproduction Data collection has been completed on a study examining the effects of dietary protein quality and quantity on intake, milk yield, and efficiency of milk production for lactating cows exposed to cool and hot weather conditions (GA). Laboratory analysis is being completed and data summarized. A study was conducted to determine the effects of three dietary cation-anion levels in diets fed immediately postpartum on performance, body temperature, and blood metabolite, hormone, and acid-base chemistry (GA). Laboratory analysis is being completed and data summarized. Feeding yeast culture to cows calving between July 28 and September 10 beginning 21 days prepartum through 21 days postpartum increased milk yield and tended to increase DMI (LA). 2b. Effect of hormonal supplements to enhance reproductive performance Hormonal treatments will be used to increase serum progesterone and compare pregnancy rates in treated and untreated cows bred during late spring (May - June) and late summer (September) (NC). Pregnancy rates will be determined 35 to 42 days after breeding. The negative effects of elevated temperature for reducing developmental potential of oocytes were not associated with changes in nuclear maturation and may be due to alterations in cytoplasmic processes (TN). An in vitro system for monitoring, in real-time, the molecular mechanisms associated with heat stress in living bovine embryos of different genotypes is being developed (MS, USVI). Embryos from Holstein, Brahman, Senepol, Holstein x Brahman and Holstein x Senepol will be obtained at specific stages of embryonic development and transfected with HSP-70-Luciferase plasmid. Heat stress will be applied to apply acute or prolonged challenges of thermal stress and changes in HSP-70 gene expression monitored. 2c. Effect of environmental modification strategies on lactational and reproductive performance A tunnel ventilation housing system to house 24 Holstein cows is being constructed and will be completed by the summer of 2001 (MS) . Studies will be conducted comparing the effectiveness of tunnel ventilation with traditional free stall housing on cow performance and comfort during heat stress.

Publications

Dorado, C. M., L. M. McCann, J. A. Miller, and J. L. Edwards. 2001. Nuclear status of bovine oocytes exposed to elevated temperature after resumption of meiosis. Theriogenology 55(1):469. (Abstr.) Ravagnolo, O., and I. Misztal. 2000. Genetic component of heat stress in dairy cattle, parameter estimation. J. Dairy Sci. 83:2126-2130. Ravagnolo, O., I. Misztal, and G. Hoogenboom. 2000. Genetic component of heat stress in dairy cattle, development of heat index function. J. Dairy Sci. 83:2120-2125. West, J. W., B. G. Mullinix, and J. K. Bernard. 2000. Influence of environmental conditions on body temperature, dry matter intake, and milk yield for lactating cows from spring through summer in the southeast. J. Dairy Sci. 83 (Suppl. 1):232. (Abstr.)

Impact Statements

Date of Annual Report: 03/25/2002

Report Information

Annual Meeting Dates: 02/02/2002 - 02/03/2002
Period the Report Covers: 01/01/2001 - 12/01/2001

Participants

John K. Bernard, Georgia; Lannett Edwards, Tennessee; Robert W. Godfrey, Virgin Islands; Bill Graves, Georgia; Debora Hamernik, USDA;
Ellen Jordan, Texas; David Morrison, Louisiana; Terry Smith, Mississippi; Jerry D. Ward, Louisiana; Joe West, Georgia; C. Scott Whisnant, North Carolina; Scott Willard, Mississippi

Participants Attachment:

Attachment

Brief Summary of Minutes

The annual meeting of the S-299 multi-state project was called to order at 9:10 a.m. on Saturday, February 2 by Chairman Scott Whisnant (NC). Present were: Lannett Edwards (TN), David Morrison (LA, Administrative Advisor), Deborah Hamernik (USDA-CSREES, Technical Advisor), Joe West (GA), John Bernard (GA), Terry Smith (MS), Bob Godfrey (U. S. VI), Scott Willard (LA), Ellen Jordan (TX), and Jerry Ward (LA). Bill Graves (GA) was a guest on February 3.

The agenda for the meeting, presented by chair Scott Whisnant, was approved. Minutes from the S-299 annual meeting in Ft. Worth were presented for discussion. Minutes were amended to include Lannett Edwards on sub-objective 8.2.B. In addition, the word oocytes was added to this objective, to reflect that the sub-objective addresses both embryos and oocytes. Amended minutes were accepted by the group.

David Morrison, administrative advisor, informed the group that there are three additions to the project; Wayne Kellogg (AR), Terry Smith (MS), and Ellen Jordan (TX). There was one withdrawal, Jean Bertrand (SC). Deborah Hamernik, technical advisor, distributed a USDA-CSREES report detailing personnel, grant funding, and changes in application dates for grants.

Minutes from the summer meeting of S-299 at Indianapolis were distributed. The web site address was amended to: http://rps.uvi.edu/S299/S299_home_page.html. Amended minutes were approved by the group. A nominating committee to select a nominee for the secretary position was appointed, and consisted of John Bernard (chair), Ellen Jordan, and Lannett Edwards.

A discussion of progress reports ensued. For procedural purposes, secretary Joe West suggested that modifications to progress reports or protocols be handled by sub-objective leaders, thus numerous modifications will not be detailed in the minutes. During discussion of sub-objective 1.a, participants agreed that cows should not receive cooling from mist or sprinkling during trials, but that fans were acceptable. John Bernard distributed a protocol for sub-objective 1.b, cooling effects on transition cows. He will send out the protocol on the listserv soon. Bob Godfrey reported that he is working on digital thermal imaging to measure heat stress effects on bulls. There was discussion of sub-objective 2.a. regarding DCAD and yeast research.

A discussion of plans for the coming year was started. For objective 1.a., GA, LA, and MS will repeat the protocol for the coming summer. Leader for this sub-objective (Joe West) will contact other states not present to determine their participation. Plans for sub-objective 1.b. focus on cooling vs. no cooling during the dry period. Sub-objective 1.c, d, e will include work determining effects of coat color, color thermography, on male fertility.

For objective 2.b., those who can generate data for studies evaluating pregnancy can sample blood for progesterone analyses, to support pregnancy data. Those who can contribute should coordinate with Scott Whisnant and Scott Willard. For objective 2.c., there is interest in evaluating air quality in the tunnel ventilation system. Participants who have other ideas regarding air quality, animal health, or other aspects should contact Terry Smith or Scott Willard.

Ellen Jordan requested input from members regarding the need to write a protocol covering cooling pond research. The cooling pond work in Texas is currently the only cooling pond work being conducted by members of S-299, but the group agreed that a protocol should be prepared for the Environmental Modification Strategies sub-objective (Objective 8.2.c.). Others can participate as opportunities develop.

In other business, the nominating committee chair (John Bernard) reported that Terry Smith was nominated for secretary for the coming year. No other nominations were made, and Terry was elected by acclamation. The group discussed the time of year and location for the next annual meeting of S-299. After extensive discussion, a motion was made to hold the 2003 annual meeting at Franklinton, LA, and time the meeting to coincide with the meeting of SAAS in Mobile, AL. The group supported the motion, and the meeting will be held on Jan. 31, Feb. 1-2 in at the LSU Ag Center facility in Franklinton. The meeting will convene on the afternoon of Friday, January 31, and will adjourn Sunday, February 2. Included in the meeting will be a tour of the new dairy facilities at the research station in Franklinton. Jerry Ward is in charge of local arrangements. There being no further business, the meeting was adjourned.

Accomplishments

Objective 1. To further elucidate direct and indirect effects of chronic heat stress in a hot, humid climate on nutrient intake and metabolism, endocrine status, and reproductive and lactational performance of dairy cattle. 1a. Effect of environmental stressors on body temperature, nutrient intake, and performance During the summer of 2001, a combined nutritional and environmental influence study was conducted (GA). Forty-two lactating cows were trained to Calan gates and fed control or treatment diets, which differed in dietary cation-anion difference (DCAD). Data collected included environmental data, dry matter intake (DMI), milk yield, milk composition, cow body weight (weekly), urinary electrolytes and blood levels of glucose, electrolytes, insulin, glucagon, cortisol and thyroxine (T4). Data are being analyzed. 1b. Effect of climate pre- and postpartum on intake and performance Studies to determine the effect of climate during the prepartum period on intake and performance postpartum will be initiated this year (GA). 1c. Effect of environmental stressors on reproductive performance (male fertility) Discussions and planning sessions have been held with 3 local dairy farmers who are willing to participate in this portion of the project. There will be some changes made to the original protocol. Due to limitations in facilities at each farm the provision of supplemental cooling for bulls will not be possible. A schedule is being established to conduct the other portions of this project. Bulls will have semen and blood collected as described initially at intervals throughout the year that represent the times of minimal and maximal heats stress. Environmental conditions will be recorded as originally described. An addition to the project will entail the use of thermal imaging equipment in cooperation with Mississippi. Bulls will have scrotal thermograms taken at specific times of the years to attempt to quantify the effect of elevated ambient temperature on testicular temperature in the Holstein bulls and compared to Senepol bulls (heat tolerant group). 1d. Effect of genetic selection on heat tolerance or intolerance The genetic component in heat tolerance for nonreturn rate in Holsteins was estimated using an animal linear model augmented by a random regression on a temperature humidity index (THI). Data consisted of 18,059 nonreturn rates at 45, 60, and 90 days after insemination and 81,674 first parity test-day milk yields from 78 herds in Florida. The THI on the day of insemination or test-day was added to each record. Only first insemination records were used. The model for nonreturn rate included the effects of herd-year-season, age, days in milk, milk yield, THI as a covariable, regular additive effect, and random regression on THI for heat-tolerance additive effect. With a single-trait model, heritability estimates for non-return (NR) NR45, NR60, and NR90 at THI=70 for first-lactation cows were 0.006, 0.014, and 0.053, respectively. Genetic correlation between regular NR90 and heat tolerance was 0.95. A bivariate analysis for NR90 and test-day milk production yielded a correlation between regular merit and heat tolerance for NR90 of 0.35, substantially lower than by the univariate model, indicating a bias in the univariate estimates caused by ignored selection. The regular genetic correlation between NR90 and milk yield was -0.41. Genetic correlation between heat tolerance for NR90 and heat tolerance for milk yield was 0.04, indicating the need to separate selection. Coat Color: The assistance of the Cooperative Extension Service at UVI has been obtained to schedule this portion of the project. Milk production records will be obtained from the DHIA database maintained for the St Croix herds by CES and the relationship with coat color will be determined. Coat color of bulls will also be compared to scrotal thermography data. Data will be collected beginning in the spring of 2002 and continue for at least 3 years. A subset of cows at each farm on St. Croix will be used and tracked throughout their life in the herd. 1e. Effect of heat stress and production level on endocrine profiles Experimental protocols for collaborating stations have been developed (AL) for the coming year. Samples will be sent from NC and possibly others to AL for analysis. Objective 2. To develop physiological, nutritional and environmental strategies to enhance milk production, reproductive performance, profitability and heat tolerance of dairy cattle in a hot, humid climate. 2a. Effect of nutritional strategies to enhance intake and efficiency of nutrient utilization and improve reproduction Data from the DCAD treatment of the experiment reported under 1a. will be included once data analysis is complete (GA). Another trial (LA) was conducted using 40 lactating cows using different DCAD and fat levels. Supplemental DCAD reduced grain intake and increased intake of a partially mixed ration consisting of silage, alfalfa hay, whole cottonseed and ryegrass haylage. Treatments had no effect on milk yield. A study was conducted to test the effectiveness of two different approaches at preventing or alleviating the detrimental effects of heat stress in lactating dairy cattle (MS). Firstly, use of the feed additive FibrozymeT , which is advertised as shifting rumen digestion of forages toward that of concentrates was tested for its ability to reduce the dietary heat increment. Secondly, in an effort to offset the detrimental effects of increased respiration rate on body chemistry, a mineral supplement (Potassium Carbonate) was tested for its ability to increase rumen buffering capacity. Lactating Holstein cows (n = 48) were placed on trial for a total of 49 days. Cows were randomly assigned to four treatment groups were balanced for age, lactation number, energy corrected milk (ECM) production and lactation somatic cell count (SCC). The four treatment groups included: Cows fed a control diet (Ctrl), which included 0.113 kg/c/d of KCl to attain a DCAD of +25. Cows fed the control supplemented with 14 g/hd/d of FibrozymeT (FIB). Cows fed the control diet supplemented with 0.226 kg/hd/d Potassium Carbonate supplied by DCAD plusT to attain a DCAD of +35 (CD). Cows supplemented with both Potassium Carbonate (DCAD plusT) and FibrozymeT (CD+FIB). Thus, the four treatments were CTRL, FIB, CD, and CD+FIB. Treatments were arranged as a two by two factorial. Each experimental group was fed a total mixed ration formulated to meet or exceed nutritional requirements of the animal. Data are being analyzed. 2b. Effect of hormonal supplements to enhance reproductive performance and studies on the response of oocytes and embryos to heat shock. A collaborative study was performed in the summer of 2001 between Mississippi and North Carolina to examine whether the administration of GnRH post-breeding might improve pregnancy rates and increase serum concentrations of progesterone during heat stress in dairy cattle. While heat stress can result in reduced hormone concentrations and lower pregnancy rates in dairy cattle, other studies have shown supplemental administration of GnRH after breeding can enhance serum concentrations of progesterone and in fact improve pregnancy rates. Therefore, the objective of this study was to examine whether GnRH administration following breeding (Day 5 vs. 11 post-breeding) would enhance reproductive performance in heat-stressed dairy cows. Our findings from this trial indicate that supplemental GnRH post-breeding will increase serum concentrations of progesterone and improve pregnancy rates of cows during summer heat stress. Additional studies will be conducted this summer. The implications of these data to the producer are that summer pregnancy rates may be improved with hormonal manipulations (e.g., GnRH). A study (TN) was designed to examine nuclear status of bovine oocytes exposed to elevated temperature after resumption of meiosis. Cumulus oocyte complexes (COC) were randomly allotted to one of four treatments and cultured at 38.5 C for 24 h (Control), 41 C for 24 h (HS024), 41 C for the first 12 h of maturation (0-12 h) followed by 38.5 C for remaining 12 h (HS012), or 38.5 C for the first 12 h of maturation followed by 41 C for remaining 12 h (12-24 h; HS1224). After 24 h, matured oocytes were denuded of cumulus; number of lysed oocytes was recorded before removal from treatment groups. Proportion of oocytes with atypical (dispersed, degenerating or condensed chromatin) versus identifiable nuclear morphologies (germinal vesicle (GV), metaphase I (MI), anaphase I (AI), telophase I (TI), or metaphase II (MII)) was recorded. Exposure of oocytes to elevated temperature, after resumption of meiosis, tended to increase proportion of lysed oocytes (P<0.1). Lysis was greatest for oocytes exposed to 41 C for 24 h (28 versus 14, 20 and 19% for Control, HS012 and HS1224, respectively; SEM=5.6). Proportion of oocytes with atypical nuclear morphologies was similar regardless of treatment (25, 24, 10 and 19% for Control, HS024, HS012 and HS1224, respectively; SEM=5.9; P=0.38). Of the oocytes with identifiable nuclear morphologies, exposure to elevated temperature did not alter ability of oocytes to progress to MII. Research done with in vitro produced embryos (FL) demonstrated that in vitro fresh but not in vitro vitrified embryos had superior pregnancy rates compared to artificial insemination. Addition of insulin-like growth factor I (IGF-I) to culture media and GnRH administration embryo recipients at day 11 post-estrus increased pregnancy rates in heat-stressed cows. Finally, embryos produced from Brahman oocytes were more resistant to heat stress than those from Holstein oocytes. Further research will determine if this is due to cytoplasmic or genetic effects of the oocyte. An in vitro system for monitoring, in real-time, the molecular mechanisms associated with heat stress in living bovine embryos of different genotypes is being developed (MS, USVI). Embryos from Holstein, Brahman, Senepol, Holstein x Brahman and Holstein x Senepol will be obtained at specific stages of embryonic development and transfected with HSP-70-Luciferase plasmid. Heat stress will be applied to apply acute or prolonged challenges of thermal stress and changes in HSP-70 gene expression monitored. Work is progressing (MS, FL) to develop novel means for monitoring the dynamics of heat shock proteins and other relevant genes in living embryos of different genotypes before, during and after exposure to heat stress. Photonic gene reporter technologies will be adapted for the real-time monitoring of gene expression in living embryos and reproductive tissues (CL, etc.). Equipment to develop these biophotonic paradigms has been obtained, and work will begin in Summer 2002. 2c. Effect of environmental modification strategies on lactational and reproductive performance Two groups of 10 lactating Holstein cows were housed in the tunnel ventilation barn (MS) and two similar groups were housed in adjacent freestall barns cooled with sprinklers and fans. Cows were randomly assigned to groups, and groups were balanced for production, parity, and DIM. The 10-week study began June 25, 2001 and was completed August 31, 2001. During the study, daily minimum and maximum environmental temperatures averaged 20.7 1 2.20C and 32.4 1 1.90C, respectively. Feed intake, refusals and milk production were recorded daily during the study. Rectal temperatures, respiration rates, and infrared surface temperatures were collected three times weekly between 1400 and 1600. The study showed that tunnel ventilation cooling decreased exposure to conditions of moderate heat stress from 345 min/d for cows housed in traditional freestall barns to 55 min/d for cows housed in the tunnel barn. The reduced heat exposure decreased the body temperatures (0.360C) and respiration rates (10.6 breaths/min) for cows housed in the tunnel ventilation barn when compared to those of cows housed outside. Furthermore, this increment in cooling improved feed consumption within the tunnel barn an average of 2 kg/d over the 10-week study. After nine weeks on the trial, milk production for cows housed inside averaged 6 lbs/hd/d more than those housed outside. These results demonstrate that dairy barns cooled by tunnel ventilation can be used to mitigate the effects of heat stress in the southeastern US. Economic analysis is being conducted in conjunction with NC to determine the cost-effectiveness of such systems. Another participant (TX) added this year will be examining the effect of cooling ponds as environmental modification on lactational and reproductive performance. Others will try to identify herds in their locations using this cooling method.

Publications

Papers: Dorado, CM, LM McCann, JA Miller, JL Edwards. 2001. Nuclear status of bovine oocytes exposed to elevated temperatures after resumption of meiosis. Theriogenology 55:469. Edwards, JL, WA King, SJ Kawarsky, AD Ealy. 2001. Responsiveness of early embryos to environmental insults: Potential protective roles of HSP70 and glutathione. Theriogenology 55:209-224. Ravagnolo, O, I Miztal. 2002. Effect of heat stress on nonreturn rate in Holsteins: Fixed-model analysis. J Dairy Sci: In Press. Ravagnolo, O, I Miztal. 2002. Effect of heat stress on nonreturn rate in Holsteins: Genetic analysis. J Dairy Sci: In Press. Ravagnolo, O, I Miztal. 2002. Studies on genetics of heat tolerance in dairy cattle with reduced weather information via cluster analysis. J Dairy Sci: In Press. West, JW, BG Mullinix, JK Bernard. 2002. Effect of hot, humid weather on milk temperature, dry matter intake, and milk yield of lactating dairy cows. J Dairy Sci: In press. Abstracts: Al-Khatani, YM, M Drost, RL Monson, JJ Rutledge, CE Krininger III, J Block, WW Thatcher, PJ Hansen. 2002. Pregnancy rates following times embryo transfer with fresh or vitrified in vitro produced embryos in lactating dairy cows under heat stress conditions. ASAS/ADSA Meetings 2002. Block, J, CC Chase, PJ Hansen. 2002. Inheritance of resistance of bovine preimplantation embryos to heat shock: Relative importance of maternal versus paternal contribution. ASAS/ADSA Meetings 2002. Block, J, M Drost, RL Monson, JJ Rutledge, RM Rivera, FF Paula-Lopes, OM Ocon, PJ Hansen. 2002. Use of insulin-like growth factor-1 in culture and administration of GnRH to recipients to improve pregnancy rates following timed embryo transfer of in vitro-produced embryos to lactating dairy cows. ASAS/ADSA Meetings 2002. Gandy, S., S. Bowers, K. Graves, A. Elias, S. Willard and C. Whisnant. 2002. Administration of GnRH post-breeding improves pregnancy rates and increases serum concentrations of progesterone during heat stress in dairy cattle. ASAS Southern Section Meetings, Orlando, FL. Smith, T.R., S. Willard, A. Chapa, T. Riley and D. Pogue. 2002. The impact of tunnel ventilation on heat stress in lactating dairy cows: Effects on body temperature and respiration rate. ASAS Southern Section Meetings, Orlando, FL. Spain, J.N., J. Sampson, D. Spiers. 2001. The relationship of indicators of thermal balance and milk production of cows on Missouri dairy farms. J. Anim. Sci. 79: Suppl. 1 p. 99.

Impact Statements

In Florida, assessment of the genetic component in heat tolerance for nonreturn rate in first-lactation Holsteins revealed heretibility estimates for nonreturn rates at 45, 60, and 90 days postpartum at THI = 70 of .006, .014, and .o53, respectively, and the genetic correlation between nonreturn rate at 90 days postpartum and heat tolerance was -.95.
In Mississippi and North Carolina, GnRH administration post-breeding increased serum concentrations of progesterone and improved pregnancy rates during summer heat stress in dairy cows.
In Tennessee, exposure of oocytes to elevated temperature after resumption of meiosis tended to increase the proportion of lysed oocytes (P< .1) and lysis was greatest for oocytes exposed to 41C for 24 hours.
In Mississippi, Holstein cows exposed to tunnel ventilation cooling for 10 weeks beginning June 25, 2001 showed increased feed intake (2 kg/d) and increased milk production (2.7 kg/day) compared with those housed in a traditional free-stall barns.

Date of Annual Report: 03/31/2003

Report Information

Annual Meeting Dates: 01/31/2003 - 02/01/2003
Period the Report Covers: 01/01/2002 - 01/01/2003

Participants

S-299 2002 Officers Present:;
Bruce Jenny, LA - Guest Administrative Advisor (for D. Morrison);
Deb Hamernik, USDA-CSREES Representative; Scott Willard, MS - S-299 Chair; Joe West, GA - S-299 Chair-Elect; Terry Smith, MS - S-299 Secretary;

Participant Members Present:; Bob Godfrey, USVI-St. Croix; Chris Wildman, GA*; Jerry Ward, LA; Logan Evans, MS*; Lannett Edwards, TN; Susan Bowers, MS*;
Scott Whisnant, NC; Stephanie Schmidt, MS*; Justin Williams, MS*;
Tim Dickerson, MS*;

Participant Members Not Present, but Reports or Correspondence of Activities Submitted:;
Peter Hansen, FL; Steve Washburn, NC; Ellen Jordan, TX; James Spain, MO;
Keith Cummins, AL; Wayne Kellogg, AR;
*Guests - Graduate Students in attendance

Brief Summary of Minutes

The meeting began at 3:00 PM on January 31st with self-introductions by the meeting participants. Administrative comments regarding S-299 activities, Multi-state reporting and federal initiatives were made by B. Jenny (S-299 guest AA for D. Morrison), and D. Hamernik (USDA-CSREES representative). The S-299 business meeting was convened in which the previous years minutes and annual report were approved unanimously. J. Ward (LA) was nominated and volunteered to serve as the S-299 Secretary for the coming year (J. West will be Chair and T. Smith will move to Chair-Elect). Members in attendance presented station reports and updates of research and collaborative arrangements. A decision was made to meet next year in Tulsa, OK on February 14 & 15, 2004 starting at 1:00 pm on Friday the 14th in conjunction with the Southern Section Animal Science meetings. The members also voted unanimously to hold the 2005 S-299 meetings in the US-Virgin Islands and to tour their research station. A date in April was suggested to minimize air and hotel rates and it was decided to invite to W-173 Animal Stress group to join S-299 for a joint meeting. Following a tour of the LSU AgCenters Southeast Research Station Dairy Facilities and documentation of collaborative arrangements for the coming year, the meeting was adjourned at 4:30 PM on February 1st.

Accomplishments

Objective I: A. Effect of environmental stressors on body temperature, nutrient intake, and performance. Accomplishment: Studies were conducted to evaluate cow body temperatures over a 24-hr period in response to heat stress, and to investigate the effectiveness of various management techniques in abating heat stress as indicated by body temperature (West GA). Using a novel tympanic membrane probe to monitor cow body temperature, dynamic fluctuations in body temperature were recorded remotely to document 24-hr changes and responses to heat stress and cooling strategies. Accomplishment: Temperatures of bedding materials were measured weekly during late summer (August to October, 2002) when high temperatures averaged 32.1o C outside and 29.9o C inside the calf barn that was open on three sides (Kellogg AR). Mean temperatures of sand (26.4o C) and granite fines (25.6o C) were cooler than other materials studied. Wheat straw was warmest (27.8o C), while rice hulls (26.9o C) and wood shavings (27.0o C) were intermediate in temperature. Straw provided the softest surface, and sand and granite fines were the hardest surfaces. The types of bedding did not affect behavior or growth performance of calves; however calves on granite fines were dirtier and calves on wood shavings were cleaner compared to the other three beddings. B. Effect of climate pre- and postpartum on intake and performance. Accomplishment: The metabolic demands of milk production can compound the effects of heat stress and negatively impact metabolic processes and production performance in lactating dairy cows. A study was performed to determine whether type of cooling system (fan vs. fan and sprinkler) influences production performance and body composition quality traits in lactating dairy cattle (Willard MS). Results indicated clear differences between high and low milk production groups in body composition traits; however cooling strategy did not influence these parameters within milk production groups. Cooling did, however, reduce heat stress as indicated by rectal temperatures, dorsal infrared body surface temperature measurements and respiration rate. C. Effect of environmental stressors on reproductive performance. Accomplishment: Reduced developmental competence of heat-shocked oocytes after the resumption of meiosis may be due to alterations in nuclear or cytoplasmic maturation. Current research is focused on examining cortical granule types and the nuclear stage of bovine oocytes matured at elevated temperatures to evaluate the effects of heat stress on oocyte competence (Edwards TN). Results thus far have shown a reduced developmental competence of heat-stressed oocytes, which may be due to specific alterations occurring in the cytoplasm during maturation. Accomplishment: Two-cell embryos are among the embryos most susceptible to elevated temperature (heat shock). Experiments are being conducted to determine ultrastructural changes in two cell embryos exposed to elevated temperature (Hansen FL). Findings indicate that exposure of 2-cell bovine embryos to elevated temperatures can disrupt embryonic development by causing alterations in the cytoskeleton, cytoplasm, nucleus and mitochondria. Accomplishment: An experiment was performed to test whether heat shock causes similar changes in embryos produced in vivo. The specific objectives were to 1) evaluate effects of a physiological heat shock on the ultrastructure of 2-cell bovine embryos produced in vivo and heat shocked ex vivo, 2) compare the ultrastructural morphology of in vitro vs. in vivo produced 2-cell embryos, and 3) determine the content of the cytoplasmic vesicles (Hansen FL). Findings indicate that exposure of in vivo produced 2-cell bovine embryos to elevated temperatures causes disruption in ultrastructural morphology that are inimical to development. Accomplishment: Heat shock, which can compromise development of preimplantation bovine embryos, also increases the percentage of blastomeres that may undergo apoptosis and increases activity of group II caspases (i.e., caspase-2, -3, and 7). It is hypothesized that apoptosis is important for the removal of damaged blastomeres and beneficial to the continued development of the embryo after heat shock. To test these hypotheses the effects of an inhibitor of group II caspases on were evaluated (Hansen FL). Findings indicate that group II caspases mediate heat-induced apoptosis in bovine embryos. Moreover, inhibition of these caspases has a detrimental effect on embryonic resistance to heat shock. Taken together these results implicate apoptosis as an adaptive mechanism to allow the embryo to survive and develop following exposure to stress. D. Effect of genetic selection on heat tolerance or intolerance. Accomplishment: Studies have addressed the interaction between coat color (black versus white percentage) and heat stress on thermal heat load in dairy cattle (Godfrey USVI). These studies have identified advantages in dairy cattle with a greater percentage of white hair-coat relative to their thermal tolerance. Accomplishment: A long-term goal is to identify genes controlling cellular thermotolerance and transfer these genes into Holstein cattle to reduce the magnitude of deleterious effects of elevated temperature on embryonic survival, immune function, and other aspects of physiological function in cattle. As part of this effort, a survey of genotypes expressing increased tolerance to heat shock at the cellular level is underway. Recently, an experiment was conducted to evaluate genetic differences in cellular thermotolerance extended to the Romosinuano, a Bos taurus developed in Colombia from the first European cattle brought to the New World (Hansen FL). These results demonstrate that embryos from thermotolerant breeds (Brahman and Romosinuano) are more resistant to elevated temperature than embryos from a thermosensitive breed (Angus). Thus, the process of adaptation of Brahman and Romosinuano breeds to hot environments resulted in both cases in selection of genes controlling thermotolerance at the cellular level. In a separate study, the production performance the genotypic differences in Gir (Bos indicus) x Holstein and Holstein cattle are also being evaluated (Willard MS). E. Effect of heat stress and production level on endocrine profiles. Accomplishment: Studies are on-going examining the hormonal profiles of Holstein cows from calving through the postpartum period for cows in summer versus winter (Whisnant NC). Results thus far have shown that cows calving during the summer have a longer interval to first ovulation than those calving during the winter, and that serum thyroid concentrations are higher in winter calving cows than in summer calving cows for the first 8 weeks postpartum. The reduced thyroid concentrations in heat stressed dairy cattle during early lactation may be directly associated with a delay in first postpartum ovulation. Objective II: A. Effect of nutritional strategies to enhance intake and efficiency of nutrient utilization and improve reproduction in hot, humid climates. Accomplishment: Studies have addressed the influence of various types of nutritional supplementation (e.g., yeast culture; Ward LA) during the transition period in dairy cattle, and will be further examined in the context of heat stress. Accomplishment: Experiments were conducted to test whether enhancement of antioxidant status could improve fertility and milk yield in dairy cows and resistance of cultured embryos to heat shock (Hansen FL). In summary, multiple injections of vitamin E and selenium did not improve postpartum fertility or milk yield of lactating Holstein cows and there was no direct thermoprotective effect of culturing heat-shocked embryos with vitamin E. Accomplishment: The relationship between dietary cation-anion difference (DCAD) and dietary crude protein (CP) in the heat-stressed lactating dairy cow was investigated to determine if changes in protein metabolism occur as a result of including cationic salts in the lactating cow total mixed ration (West GA). The relationship was examined at DCAD of 25 and 50 meq/100 g DM combined with CP levels of 15 and 17%. Results indicate a relationship exists between DCAD and protein metabolism. High DCAD resulted in lower average daily milk yields at high CP level when compared to low DCAD high CP diets. A relationship was also observed in blood and urine Na levels. At low CP, blood Na decreased with increasing DCAD. At high CP, blood Na increased with increasing DCAD. In addition, a more dramatic increase in fractional excretion of Na was observed at low CP with increasing DCAD relative to the increase observed with the high CP diet. B. Effect of hormonal supplements to enhance reproductive performance in hot, humid climates. Accomplishment: Studies have been conducted in a collaborative effort among three stations (Godfrey USVI; Whisnant NC; Willard MS) to evaluate the effects of supplemental GnRH administration post-breeding on endocrine profiles and pregnancy rates in heat stressed dairy cows and heifers. While somewhat variable results have been obtained among these studies to date with respect to pregnancy rates, further analysis is continuing to determine whether such a hormonal therapy would be advantageous during heat stress as the endocrine profiles of the treated cows suggests marked improvement of their hormonal status post-breeding. Accomplishment: Administration of bovine somatotropin (bST) improves pregnancy rates following timed artificial insemination in lactating dairy cows. Two experiments tested whether bST administration to non-lactating recipients improves pregnancy rates following transfer of in vitro produced embryos (Hansen FL). Results indicate that breed of recipient but not bST administration affects pregnancy rates in non-lactating recipients following timed embryo transfer with IVP embryos. C. Effect of environmental modification strategies on lactational and reproductive performance in hot, humid climates. Accomplishment: One controversial cooling method for managing heat stress is the utilization of cooling ponds. A survey was sent to Texas dairy producers who might have cooling ponds, and general information regarding the use of the cooling ponds was collected along with milk quality information (E. Jordan TX). Results indicated that for the major pathogens the presence or absence of a cooling pond did not influence the number of organisms identified. From these results, the use of cooling ponds does not increase bacterial populations in bulk tank milk samples. The herds examined with cooling ponds produced 2.62 kg of milk/milking cow/day more in August than did herds without cooling ponds. Herds with cooling ponds also produced more milk in June, July, September and October than herds without cooling ponds. No differences were found in culling patterns between the two groups. Accomplishment: A lactation trial was performed to characterize the impact of tunnel ventilation cooling and diet on symptoms of heat stress in dairy cows (Smith MS). Average exposure time to conditions of moderate heat stress was reduced 6.75 h/day for cows housed in the tunnel ventilation barn and maximal daytime rectal temperatures for cows housed inside averaged 0.28oC below those for cows housed outside. Furthermore, the maximal daytime respiration rate averaged 6.0 breaths/min lower for cows housed inside the tunnel barn than for cows housed outside. These results demonstrate that barns equipped with tunnel ventilation can be helpful in reducing the severity of heat stress on dairy cows in the southeastern U.S.

Publications

Refereed Journals and Peer-Reviewed Proceedings: Al-Katanani, Y.M., Paula-Lopes, F.F., and Hansen, P.J. (2002) Effect of season and exposure to heat stress on oocyte competence in Holstein cows. J. Dairy Sci. 85, 390-396. Al-Katanani, Y.M., Rivera, R.M., and Hansen, P.J. (2002) Seasonal variation in development of in vitro produced bovine embryos. Vet. Rec., 150, 486-487. Al-Katanani, Y.M., and Hansen, P.J. (2002) Induced thermotolerance in bovine two-cell embryos and the role of heat shock protein 70 in embryonic development. Mol. Reprod. Dev. 64, 174-180. Al-Katanani, Y.M., Drost, M., Monson, R.L., Rutledge, J.J., Krininger III, C.E., Block, J., Thatcher, W.W., and Hansen, P.J. (2002) Pregnancy rates following timed embryo transfer with fresh or vitrified in vitro produced embryos in lactating dairy cows under heat stress conditions. Theriogenology 58, 171-182. Block, J., Chase, C.C., Jr., and Hansen, P.J. (2002) Inheritance of resistance of bovine preimplantation embryos to heat shock: relative importance of the maternal vs. paternal contribution. Mol. Reprod. Dev.63, 32-37. Block, J., Drost, M., Monson, R.L., Rutledge, J.J., Rivera, R.M., Paula-Lopes, F.F., Ocon, O.M., Krininger, C.E. III, Liu, J., and Hansen, P.J. (2003) Use of insulin-like growth factor-1 during embryo culture and treatment of recipients with GnRH to increase pregnancy rates following the transfer of in vitro produced embryos to heat-stressed, lactating cows. J. Anim. Sci., (accepted). Dorado, C.M., L.M. McCann, J.A. Miller and J.L. Edwards. 2001. Nuclear status of bovine oocytes exposed to elevated temperature after resumption of meiosis. Theriogenology 55(1):469. Edwards J.L., W.A. King, S.J. Kawarsky and A.D. Ealy. 2001. Responsiveness of early embryos to environmental insults: Potential protective roles of HSP70 and glutathione. Theriogenology 55(1):209-224. Hansen, P.J. (2002) Embryonic mortality in cattle from the embryos perspective. J. Anim. Sci. 80 (E. Suppl. 2): E33-E44. Jordan, E.R., T. Hickerson, and M. Tomaszewski. 2003. Evaluation of the effects of cooling ponds on bacterial population in bulk tank milk samples. Proc. of the 42nd National Mastitis Council Conference. p. 316?317. Krininger, C.E. III, Stephens, S.H., and Hansen, P.J. (2002) Developmental changes in inhibitory effects of arsenic and heat shock on growth of preimplantation bovine embryos. Mol. Reprod. Dev. 63:335-340. Krininger III, C.E., Block, J., Al-Katanani, Y.M., Rivera, R.M., Chase, C.C., Jr., and Hansen, P.J. (2003) Differences between Brahman and Holstein cows in response to estrous synchronization, superovulation and resistance of embryos to heat shock. Anim. Reprod. Sci., (in press). Moreira, F., Paula-Lopes, F.F., Hansen, P.J., Badinga, L., and Thatcher, W.W. (2002) Effects of growth hormone and insulin-like growth factor-I on development of in vitro derived bovine embryos. Theriogenology, 57, 897-905. Paula-Lopes, F.F., and Hansen, P.J. (2002) Heat-shock induced apoptosis in preimplantation bovine embryos is a developmentally-regulated phenomenon. Biol. Reprod., 66, 1169-1177. Paula-Lopes, F.F., and Hansen, P.J. (2002) Apoptosis is an adaptive response in bovine preimplantation embryos that facilitates survival after heat shock. Biochem. Biophys. Res. Commun. 295, 37-42. Paula-Lopes, F.F., Chase, C.C., Jr., Al-Katanani, Y.M., Krininger, C.E. III, Rivera, R.M., Tekin, S., Majewski, A.C., Ocon, O.M., Olson, T.A., and Hansen, P.J. (2003) Genetic divergence in cellular resistance to heat shock in cattle: Differences between breeds developed in temperate versus hot climates in responses of preimplantation embryos, reproductive tract tissues and lymphocytes to increased culture temperatures. Reproduction 125, 285-294. Paula-Lopes, F.F., Al-Katanani, Y.M., Majewski, A.C., McDowell, L.R., and Hansen, P.J. (2003) Manipulation of antioxidant status fails to improve fertility of lactating cows or survival of heat-shocked embryos. J. Dairy Sci., in press. Rivera, R.M., Kelley, K.K., Erdos, G.W., and Hansen, P.J. (2002) Heat shock induces ultrastructural changes in two-cell bovine embryos. The Beam 18 (1): 11-19. Rivera, R.M., Kelley, K.K., Erdos, G.W., and Hansen, P.J. (2002) Heat shock induces ultrastructural changes in two-cell bovine embryos. Proc. Ann Mtg. Southeastern Microscop. Soc., p 11. Willard, S., S. Gandy, S. Bowers, K. Graves, A. Elias and C. Whisnant. 2003. The effects of GnRH administration post-breeding on serum concentrations of progesterone and pregnancy rates in dairy cattle exposed to mild summer heat stress. Theriogenology 59(8): 1799-1810. Meeting Abstracts and Experiment Station Reports: Block, J., Drost, M., Monson, R.L., Rutledge, J.J., Rivera, R.M., Paula-Lopes, F.F., Ocon, O.M., and Hansen, P.J. (2002) Use of insulin-like growth factor-1 in culture and administration of GnRH to recipients to improve pregnancy rates following timed embryo transfer of in vitro-produced embryos to lactating dairy cows. J. Anim. Sci. 80 (Suppl. 1), 78 (abstr.). Block, J., Chase, C.C., and Hansen, P.J. (2002) Inheritance of resistance of bovine preimplantation embryos to heat shock: relative importance of the maternal versus paternal contribution. Biol. Reprod. 66 (Suppl. 1): 154 (abstr.). Block, J., Monson, R.L., Rutledge, J.J., Rivera, R.M., Paula-Lopes, F.F., Ocon, O.M., Rosson, H., Al-Katanani, Y.M., and Hansen, P.J. (2003) Effect of bovine somatotropin, breed, and circulating progesterone concentrations at the time of transfer on pregnancy rates following timed embryo transfer in non-lactating cows. J. Anim. Sci., submitted (abstr.). Evans, H.L., S.T. Willard, B.J. Boyd and R.C. Vann. 2002. Dynamic changes in body composition quality traits as influenced by sampling interval in beef heifers. 2001 Central Mississippi R & E Progress Report. Gandy, S., S. Bowers, K. Graves, A. Elias, S. Willard and C. Whisnant. 2002. Administration of GnRH post-breeding improves pregnancy rates and increases serum concentrations of progesterone during heat stress in dairy cattle. ASAS Southern Section Meetings, Orlando, FL February 1 6, 2002; Abstract 66 pg. 17. Godfrey, R.W., R.E. Dodson, A.J. Weis and O.T. Isles. 2003. The effect of using of Ovsynch with supplemental GnRH on pregnancy rates of Holstein heifers in the tropics. Submitted to 2003 National Animal Science meeting, Phoenix, AZ (Accepted / To be Presented). Godfrey, R.W., O.T. Isles, A.J. Weis and R.E. Dodson. 2003. The effect of hair coat color on rectal and surface temperatures of Holstein heifers in the tropics. Submitted to 2003 National Animal Science meeting, Phoenix, AZ (Accepted / To be Presented). Nordbladh, L.I., A.E. Sweetman and C.S. Whisnant. 2003. Effect of season on serum thyroxine and beta-hydroxy butyrate concentrations in early postpartum dairy cows. Submitted to 2003 National Animal Science meeting, Phoenix, AZ (Accepted / To be Presented). Paula-Lopes, F.F., and Hansen, P.J. (2002) Administration of the caspase inhibitor, z-DEVD-fmk, to bovine preimplantation embryos blocks heat-induced apoptosis and increases embryonic sensitivity to heat shock Biol. Reprod. 66 (Suppl. 1): 105 (abstr.). Panivivat, R., Kegley, E.B., Kellogg, D.W., Pennington, J.A. VanDeveder, K., Hellwig, D.H., Wistuba, T.J., and Krumpleman S.L. 2002. Preference for and bacterial counts in sand and granite fines as bedding for lactating cows. University of Arkansas Agric. Exp. Sta. Res Series 499. Pages 143-146. Payton R.R., J.L. Lawrence, A.M. Saxton, J.R. Dunlap, and J.L. Edwards. 2002. Cortical granule types and nuclear stage of bovine oocytes after exposure to elevated temperature during maturation. (Abstract accepted for publication at International Embryo Transfer Society Meetings to be held in Auckland, New Zealand, January 11-15, 2003). Rivera, R.M., Kelley, K.L., Erdos, G.W., and Hansen, P.J. (2003) Exposure of in vivo produced 2-cell bovine embryos to a physiological-relevant heat shock results in alterations to the ultrastructural morphology. Biol. Reprod., submitted (abstr.). Rivera, R.M., Kelley, K.K., Erdos, G.W., and Hansen, P.J. (2002) Heat shock induces ultrastructural changes in two-cell bovine embryos. Biol. Reprod. 66 (Suppl. 1): 158-159 (abstr.). Smith, T.R., S. Willard, A. Chapa, T. Riley and D. Pogue. 2002. The impact of tunnel ventilation on heat stress in lactating dairy cows: Effect on body temperature, respiration rate and milk production. 2001 North Mississippi R & E Progress Report. Smith, T.R., S. Willard, A. Chapa, R. J. Williams, T. Riley, and D. Pogue. 2002. The impact of tunnel ventilation on heat stress in lactating dairy cows: Effects on intake, milk production and composition. J. Dairy Sci. 85 (Suppl. 1): Abstr. 1236. Smith, T. R., S. Willard, A. Chapa, T. Riley, and D. Pogue. 2002. The impact of tunnel ventilation on heat stress in lactating dairy cows: Effects on body temperature and respiration rate. J.Ani.Sci. 80(Suppl. 2): Abstr. 98. Sweetman, A.E., L.I. Nordbladh, and C.S. Whisnant. 2003. Effect of administration of GnRH on day 5 or day 5 and 11 post-insemination on pregnancy rates and serum progesterone concentrations of lactating dairy cows during different seasons. Submitted to 2003 National Animal Science meeting, Phoenix, AZ (Accepted / To be Presented). Tomaszewski, M.A., M.A. de Haan, J.A. Thompson, and E.R. Jordan. 2003. The impact of cooling ponds in north central Texas on milk production and culling. J. Dairy Science - abstr. (submitted). Ward, J. D. 2002 .The effects of supplementing yeast culture during the transition period on performance of Holstein cows during hot humid weather. J. Dairy Sci. 85 (suppl. 1):119. Willard, S.T. and E.J. Murphy. 2002. Economic and Production Differences Between Large and Small Holstein Cows Cooled with Fans and Sprinklers or Fans Only. 2001 Central Mississippi R & E Progress Report. Williams, R., A. M. Chapa, T. O. Riley, D. E. Pogue, S. T. Willard and T. R. Smith. 2003. The impact of tunnel ventilation cooling and bmr corn silage on heat stress in lactating dairy cows. North MS Res. & Ext Center Annual Report. p. 191.

Impact Statements

Novel methods for charting body temperature in lactating dairy cows during heat stress will provide improved methodologies to assess the effectiveness of cooling strategies in mediating or abating heat stress in dairy cows.
Better understanding of the negative effects of heat stress at the cellular and molecular level will be critical for development of novel strategies for improving reproduction and embryonic survival during heat stress.
Through a greater understanding of the effects of heat stress on the ultrastructure of the developing embryo, we may better understand how elevated temperatures may compromise the establishment of pregnancy.
The identification of the specific genes involved in thermotolerance among breeds could lead to novel ways to increase resistance of cattle to heat stress.
A better understanding of the effect of acid-base balance on protein metabolism will enhance the effectiveness with which the protein needs of the heat-stressed cow are met at reduced intake levels that occur as a result of heat-stress.
Cooling ponds may represent an effective method for improving production performance during heat stress in some regions, and results indicate that bacterial loads in milk were not increased as might be expected
Barns equipped with tunnel ventilation can be helpful in reducing the severity of heat stress on dairy cows in the southeastern U.S.
An enhanced understanding of how the embryo responds and overcomes a heat-induced response is critical toward developing systems that may increase embryo survival during heat stressed conditions
Through dietary manipulation using targeted nutritional supplementation, the effects of heat stress may be abated to some extent
Vitamin E was not found to be beneficial to postpartum cow performance or in the survivability of heat-shocked embryos, therefore should not be recommended until further research can be conducted
A better understanding of the effect of acid-base balance on protein metabolism will enhance the effectiveness with which the protein needs of the heat-stressed cow are met at reduced intake levels that occur as a result of heat-stress

Date of Annual Report: 05/25/2004

Report Information

Annual Meeting Dates: 02/14/2004 - 02/15/2004
Period the Report Covers: 01/01/2003 - 12/01/2003

Participants

West, Joe (jwest@tifton.cpes.peachnet.edu) - University of Georgia; Smith, Terry (trsmith@ads.msstate.edu) - Mississippi State University; Ward, Jerry (jward@agcenter.lsu.edu) - LSU AgCenter; Edwards, Lynette (jedwards@utk.edu) - University of Tennessee; Whisnant, Scott - North Carolina State University; Willard, Scott (swillard@ads.msstate.edu) - Mississippi State University; Godfrey, Bob (rgodfre@uvi.edu) - University of Virgin Islands; Kellogg, Wayne - University of Arkansas; Williams, Justin - Mississippi State University; Hamernik, Deb - USDA-CSREES; Morrison, David (dmorrison@agcenter.lsu.edu) - LSU AgCenter

Brief Summary of Minutes

The meeting came to order at 8:15 am on February 14 in Tulsa, OK with a welcome and self-introductions. The agenda and related information for the meeting were approved. David Morrison stressed that this was an important meeting in the life of the project as it was the midterm meeting. He stressed that it was important to make future plans for the project if it was to continue. There are two options: 1) extend the project one year if it was incomplete, or 2) begin the process of writing another project. It was decided to begin the process of writing. There are numerous deadlines that must be met to initiate another project. The group agreed that it would be beneficial to meet during the National Animal and Dairy Science Meeting in St. Louis to discuss writing responsibilities. David Morrison gave an update on the mid-term review of the project conducted in January at the Department Heads Meeting. The review committee was pleased with the science that was being conducted but was concerned about the lack of shared protocols and overall lack of collaboration. The group has a better understanding of the need for shared protocols and increased collaboration. Deb Hamernick gave an update on personnel changes at USDA, the Competitive Grants Program, the USDA grants budget and the Presidents proposed budget for next year.

The remainder of the Saturday sessions was spent sharing reports from research conducted last year. A general discussion of suggestions for areas of research and collaboration for the new project lead to a number of ideas (in the complete minutes). It was mentioned that more effort should be expended looking for grants and funding to support work done under this project. A working mission statement was developed as well as a rough schematic showing the areas of research and the interaction between them. To facilitate collaboration, a questionnaire for the group to build a facilities, laboratory, and capabilities database will be distributed. A discussion was held to identify collaborative areas of research for the coming year.

The 2005 annual meeting schedule was discussed and the date set. Bob Godfrey agreed to host the meeting at UVI. The dates were set for May 22-23 with participants arriving on the afternoon of Saturday May 21. The meeting adjourned at noon on February 15.

Accomplishments

Objective I: A. Effect of environmental stressors on body temperature, nutrient intake, and performance. Accomplishment: Vaginal temperature was not different (P > 0.10) between dark and light Holstein cows for coat color (Godfrey-VI). Peak skin and vaginal temperatures lagged behind peak environmental temperature by 157 and 278 min, respectively. Temperature under white or black hair and vaginal temperature were correlated with environmental temperature (P < 0.0001; r = 0.38, 0.38 and 0.21 respectively). Dark cows tended to have higher (P < 0.07) maximum black coat temperatures than did light cows. Wetting cows decreased body temperature and increased milk production (Ward-LSU). There were larger milk responses in older cows compared with heifers, and cows responded to sprinkling to a greater degree than heifers in the afternoon. Cows and heifers that were sprinkled had slightly higher body temperatures in the morning. The sprinklers were turned off at 7 pm and all animals had the same amount of cooling during the night time. With the greater milk production the assumption was that sprinkled cows were consuming more feed and the increased heat of fermentation caused by increased feed intake led to the slightly higher body temperatures in the morning. Temperatures of bedding (sand, rice hulls, and a mixture of sand and rice hulls) were measured in 36 free stalls used by lactating cows (Kellogg - AR). Additionally, SandTrapTM devices were used to hold bedding in all of the stall or in only one-half of the stall. The air temperature averaged 31.5oC outside and 29.1oC inside the free stall barn. Sand bedding was warmer in the front of the stalls when the entire SandTrapTM was used (30.4 vs. 31.8oC), but bedding temperatures at the back of stalls did not differ between use of one-half and entire SandTrapTM devices. Accomplishment: The effects of cooling Holsteins during the prepartum period were investigated using 30 cows (Ward, LA). One half of the cows were housed under fans and sprinklers and the other half only had access to shade. Cooling had no effect on body temperature or DMI prior to calving and had no effect on milk production after calving. However, cooling prior to calving decreased DMI after calving. B. Effect of environmental stressors on reproductive performance. Accomplishment: Progress in characterizing components of the oocyte altered by elevated temperature has been made (Edwards, TN). Heat shock did not alter nuclear maturation as culture at 41ºC for up to 24 h and did not alter progression of the oocyte to metaphase. Heat shock did not alter membrane integrity as culture at 41ºC for up to 24 h, did not alter proportion of oocytes recovered, lysed, or having an intact membrane after cumulus denudement. Heat shock did alter a number of components within the egg cytoplasm. Cortical granule types were altered after heat shock suggesting possible alterations in the cytoskeleton. Glutathione content was elevated in the oocyte after heat shock suggesting possible increases in free radicals. Retinol improved the development of oocytes compromised by heat stress. C. Effect of genetic selection on heat tolerance or intolerance. Accomplishment: Days open (DO) records from GA, TN and NC were analyzed accounting for heat stress via a norm-reaction model (Misztal, GA). The shape of the heat index for DO was close to sinusoidal with the highest value in April and the lowest value in October. Genetic and residual variances and heritabilities were highest for spring calvings and lowest for fall calvings. The variance associated with the highest level of heat index was 33% of the genetic variance under no heat stress. Genetic correlation between regular and heat stress effects was 0.67. Studies have addressed the interaction between coat color (black versus white percentage) and heat stress on thermal heat load in dairy cattle (Godfrey - USVI). Pictures of cows on heat stress trials during the summer of 2003 (Willard, MS) have been acquired, and will be analyzed in cooperation with Godfrey - USVI and included as a parameter in study analysis and future experimental designs. These studies thus far have identified advantages in dairy cattle with a greater percentage of white hair-coat relative to their thermal tolerance. A survey of genotypes expressing increased tolerance to heat shock at the cellular level is underway (Hansen - FL). In cooperation with this aim, the production performance and genotypic differences in Gir (Bos indicus) x Holstein and Holstein cattle are being evaluated (Willard-MS). Cross-bred heifers and bulls have reached one-year of age as of this progress report, and growth curves are being analyzed relative to Holstein companions. Gir x Holstein heifers are currently being added to the breeding herd for artificial insemination to Holstein sires, and crossbred bulls are being ejaculated to assess timing of puberty and ejaculate quality. D. Effect of heat stress and production level on endocrine profiles. Accomplishment: The concentrations of metabolites and hormones during the 12 weeks after calving in dairy cows calving in either summer (August) or winter (January) were compared (Whisnant - NC). Serum P4 concentrations increased earlier in winter indicating an earlier first ovulation. Levels of non-esterified fatty acids and beta hydroxy butyrate were higher and cholesterol was lower in summer cows. These may indicate that summer cows were in a poorer nutritional state than winter cows. Serum leptin concentrations were higher in summer cows, which may reflect photoperiod differences. Concentrations of glucose, insulin and plasma urea nitrogen (PUN) and thyroxine (T4) did not differ between seasons. Thyroxine and PUN levels increased gradually over time in both groups. Objective II: A. Effect of nutritional strategies to enhance intake and efficiency of nutrient utilization and improve reproduction in hot, humid climates. Accomplishment: The effect of feeding a fibrolytic enzyme or yeast on production and energy sttus of lactating Holsteins was investigated (Smith, Willard, MS; Ward, LA) Dietary treatments were: 1) fibrolytic enzyme (7g/d in LA; 15 g/d in MS), 2) 113 g/d yeast or 3) controls. In LA, dietary treatment had no effect on DMI, milk production, milk composition, or blood NEFA or glucose concentrations. In MS, cows supplemented with yeast and Fibrozyme averaged 4.2% and 9.3% greater feed intake than controls and during the final 3 weeks of the study, the difference in feed intake became more pronounced for cows supplemented with Fibrozyme; in this period their intake averaged 15% greater than controls. The dietary supplements used had no impact on cow body temperatures or respiration rates. Accomplishment: Trials investigated the relationship between DCAD (25 or 50 meq Na+K-Cl/100 g DM) and dietary crude protein (CP) concentrations (14.5 or 16.8% CP) and the relationship between DCAD (25 or 50 meq/100 g DM) and protein degradability (15% CP with either 33 or 42% of CP as undegradeable intake protein (UIP)(West, Bernard, GA). Increasing DCAD improved DMI and yield of milk, fat, protein. Blood bicarbonate was higher and urinary N was lower for the high DCAD. An interaction was observed between DCAD and UIP for DMI and yield of milk, fat, and protein because of improved intake and yield for high DCAD at 33% UIP where intake and yield were similar for both DCAD concentrations at 42% UIP. Urinary urea N excretion was greater for low DCAD and for 33 versus 42% UIP. B. Effect of hormonal supplements to enhance reproductive performance in hot, humid climates. Accomplishment: Studies have been conducted (Godfrey-USVI; Whisnant-NC; Willard-MS) to evaluate supplemental GnRH administration post-breeding on endocrine profiles and pregnancy rates in heat stressed dairy cows and heifers. Results have been variable among location with respect to pregnancy rates and further analysis is continuing. Accomplishment: Administration of GnRH to heat stressed dairy cows on either day 5, or day 5 and 11 after insemination to a timed AI in heat stressed dairy cows was tested (Whisnant-NC). A similar treatment was performed in winter for comparison. During summer, the temperature-humidity index (THI) values averaged 76.0, which is considered mild heat stress. Serum P4 was increased by GnRH administration in both groups. Pregnancy rates were higher in the cows receiving GnRH on both days 5 and 11 (35.7-2.4%) than in controls (14.5-1.5%) and in cows receiving GnRH on day 5 only (22.8-5.5%). In winter, GnRH administration increased serum P4 concentrations but had no effect on pregnancy rates. Pregnancy rates were 25% in both controls and the day 5 group and 33% for the day 5 and 11 group. Although not a planned comparison, serum P4 concentrations were higher in control (no supplemental GnRH) cows in winter than in control cows sampled during the summer. This seasonal difference was also seen in other treatment groups, confirming earlier reports of lower P4 in cows under heat stress conditions. C. Effect of environmental modifications on lactational and reproductive performance in hot, humid climates. Accomplishment: To characterize the impact of tunnel ventilation cooling on lactation performance during periods of hot weather (Smith, Willard-MS). A 10-week trial, which began June 2, 2003, compared two groups of 10 cows housed in the tunnel ventilation barn with two similar groups, housed in an adjacent traditional freestall barn, cooled by shade and fans alone. Tunnel ventilation cooling decreased exposure to moderate heat stress conditions by 4.3 hours/d when compared to conditions in the traditional freestall barns. Cows housed in the tunnel barn had dramatically lower peak body temperatures (1.2 OF) and respiration rates (15.7 breaths/min) than cows housed in the outside freestall barn. Cooling improved feed consumption an average of 4.0 lbs/hd/d. In addition, cows receiving the tunnel ventilation cooling averaged 5.9 lbs/hd/d greater milk production than cows cooled with shade and fans alone. Cows housed in a tunnel ventilation barn were compared for reproductive performance with a similar group of cows housed in an adjacent traditional freestall barn, cooled by shade and fans alone (Smith, Willard-MS). Cows were synchronized using 2-injections of PGF2a over 14 d, and observed continuously for signs of estrous activity. The average duration of estrus was shorter for cows in the tunnel barn than for those housed outside 6.78+0.87 h vs. 10.33+3.24 h, respectively. Cows in the tunnel barn tended to exhibit signs of estrus earlier in the day than cows housed outside. The pregnancy rate was 37.5% for cows housed in tunnel barn and 25% for cows housed outside. The use of fans only and fans plus sprinklers was explored to evaluate animal production in relation to size of cow (Large or Small); Willard,MS). The cows were housed in a free stall barn. Rectal temperatures, dorsal and ventral infrared temperature (DIR and VIR) and ventral infrared temperature (DIR and VIR) and respiratory rates did not differ in relation to size of the cow. However, the cows in the fan and sprinkler groups had lower rectal temperature, VIR, DIR, and respiratory rate than the cows in the fan only group. Milk production followed the same pattern with size of the cow having no affect, but the groups that were cooled with the fan and sprinkler produced more milk throughout the trial. Daily income per cow was greatest for the small animals cooled by fan and sprinkler followed by the larger animals cooled with fan and sprinkler, the small cows cooled by fans, and then the large animals cooled by fans. In addition when the economics of the cooling systems and DMI were calculated, daily income per cow was greatest for the small cow fan and sprinkler group.

Publications

Edwards J.L., W.A. King, S.J. Kawarsky and A.D. Ealy. 2001. Responsiveness of early embryos to environmental insults: Potential protective roles of HSP70 and glutathione. Theriogenology 55(1):209-224. Lawrence J.L., R.R. Payton, J.D. Godkin, A.M. Saxton, F.N. Schrick and J.L. Edwards. 2004. Retinol improves development of bovine oocytes compromised by heat stress during maturation. J. Dairy Sci. (In press). Nobre, P. R. C. , I. Misztal , S. Tsuruta, J. K. Bertrand, L. O. C. Silva, and P. S. Lopes. 2003. Analyses of Growth Curves of Nelore Cattle by Multiple Trait and Random Regression Models. J Anim. Sci. 81:918-926. Oseni, S., I. Misztal, S. Tsuruta, and R. Rekaya. 2003. Seasonality of Days Open in US Holsteins. J. Dairy Sci. 86:3718-3725. Van Tassell, C. P., G. R. Wiggans, and I. Misztal. 2003. Implementation of a Sire-Maternal Grandsire Model for Evaluation of Calving Ease in the United States. J. Dairy Sci. 86: 3366-3373. West, J. W., B. G. Mullinix, and J. K. Bernard. 2003. Effects of hot, humid weather on body temperature, dry matter intake, and milk yield of lactating dairy cows. J. Dairy Sci. 86:232-242. Wiggans, G. R., I. Misztal, and C. P. Van Tassell. 2003. Calving Ease (Co)Variance Components for a Sire-Maternal Grandsire Threshold Model. J. Dairy Sci. 86:1845-1848. Willard, S., S. Gandy, S. Bowers, K. Graves, A. Elias and C. Whisnant. 2003. The effects of GnRH administration post-breeding on serum concentrations of progesterone and pregnancy rates in dairy cattle exposed to mild summer heat stress. Theriogenology 59(8): 1799-1810. Meeting Abstracts and Experiment Station Reports: Bohmanova, J., I. Misztal, and J. Pribyl. 2003. Differences in growth trajectories in seven beef breeds. J. Anim. Sci. (Suppl.) 81:198. Dickerson, T., K. Graves, J. White, S. Bowers, L. Evans, B. Gandy, S. Schmidt and S. Willard. 2003. The effects of supplemental GnRH administration following OvSynch on pregnancy rates of lactating dairy cattle during the summer and fall seasons. J. Dairy Science 86 (Suppl. 1): 179 (Abstr. M4; ASAS/ADSA 2003 National Meeting, Phoenix, AZ). Dorado, C.M., L.M. McCann, J.A. Miller and J.L. Edwards. 2001. Nuclear status of bovine oocytes exposed to elevated temperature after resumption of meiosis. Theriogenology 55(1):469. Evans, H.L., R.C. Vann, J. Murphy, E.J. Cuadra and S.T. Willard. 2003. The effect of cooling strategy during summer heat stress on production performance and body composition quality traits in lactating Holstein dairy cattle. 2002 Central Mississippi R & E Progress Report. Evans, H., J. Murphey, E. Cuadra, T. Dickerson, S. Gandy, S. Willard and R. Vann. 2003. The effects of cooling strategy and level of milk production on milk constituents and body composition quality traits during summer heat stress in lactating Holstein dairy cattle. J. Dairy Science 86 (Suppl. 1): 281 (Abstr. T181; ASAS/ADSA 2003 National Meeting, Phoenix, AZ). Evans, H.L., J. Murphy, E. Cuadra, S.T. Willard and R.C. Vann. 2003. The effect of cooling strategy during summer heat stress on production performance and body composition quality traits in lactating Holstein dairy cattle. ASAS Southern Section Meetings, Mobile, AL January 31 ? 4, 2003; Abstract 57, pg. 15. Godfrey, R.W., Isles, O.T., Weis, A.J. and R.E. Dodson. 2003. The effect of hair coat color on rectal and surface temperatures of Holstein heifers in the tropics. J. Anim. Sci. 81(Suppl. 1):145. Godfrey, R.W., Dodson, R.E., Weis, A.J. and O.T. Isles. 2003. The effect of using Ovsynch with supplemental GnRH on pregnancy rates of Holstein heifers in the tropics. J. Anim. Sci. 81(Suppl. 1):145. Lawrence J.L., R.R. Payton, J.D. Godkin, A.M. Saxton, F.N. Schrick, J.L. Edwards. 2003. Development of heat-stressed oocytes matured in the presence of retinol. Biol. Reprod. 68(1):344. Legarra, A., I. Misztal1, and J. Jamrozik. 2003. Plotting covariance functions from random regression models. J. Dairy Sci (Suppl. 1) 86:114. Misztal, I., S. Oseni, and S. Tsuruta. 2003. Analyses of heat tolerance for milk in Holsteins using different sources of heat-stress information. J. Dairy Sci (Suppl. 1) 86:39. Nordbladh, LI, AE Sweetman, CS Whisnant. 2003. Postpartum changes in hormones and metabolites during early lactation in summer and winter calving Holstein cows. J. Anim Sci. 81: Suppl.1, p 298. Oseni, S., and I. Misztal. 2003. Seasonality of days open in US Holsteins. J. Dairy Sci (Suppl. 1) 86: 131. Panivivat, R., Pennington, J.A., Kegley, E.B., Kellogg, D.W., and Krumpelman, S.L. 2003. Growth performance and health of dairy calves bedded with different types of materials. J. Dairy Sci. 86(Suppl.1):280. Panivivat, R., Kegley, E.B., Kellogg, D.W., Pennington, J.A. VanDeveder, K., Hellwig, D.H., Wistuba, T.J., and Krumpleman S.L. 2003. Growth performance and health of dairy calves bedded with different types of materials. University of Arkansas Agric. Exp. Sta. Res. Series 509. Pages 83-87. Payton R.R., P. Coy, R.R., A.M. Saxton, J.L. Lawrence, J.L. Edwards. 2003. Heat stress reduces development of germinal vesicle-stage bovine oocytes. Biol. Reprod. 68(1):343. Payton, R.R., P. Coy, R. Romar, J.L. Lawrence, J.L. Edwards. 2003. Heat shock increases glutathione content in bovine oocytes. J. Anim. Sci. 86(1):3. Payton R.R., J.L. Lawrence, A.M. Saxton, J.R. Dunlap, and J.L. Edwards. 2003. Cortical granule types and nuclear stage of bovine oocytes after exposure to elevated temperature during maturation. Theriogenology 59(1):496. Sapp, R. L., R. Rekaya, J. K. Bertrand, I. Misztal, and K. A. Donoghue. 2003. Genetic parameter estimates of udder scores in Gelbvieh cattle. J. Anim. Sci. (Suppl.) 81:88. Schmidt, S.J., B.S. Gandy, F. Hoholm, K. Graves, J. White, S.T. Willard. 2003. Physiology of pregnancy and calving characteristics of Holstein cows bred to Holstein or Gir (Bos indicus) sires. J. Dairy Science 86 (Suppl. 1): 143 (Abstr. 567; ASAS/ADSA 2003 National Meeting, Phoenix, AZ). Smith, T.R., A. Chapa, D. Pogue, T. Riley, J. Williams, J. Crouch and Heather Wilson. 2004. Tunnel ventilation cooling for lactating dairy cows during hot weather: 2. Comparison to cooling with shade and fans. Annual Report 2003 of the North Mississippi Research & Extension Center, Mississippi Agriculture & Forestry Experiment Station Information Bulletin. Sweetman, AE, LI Norbladh, CS Whisnant. 2003. Effect of administration of GnRH on day 5 or day 5 and 11 post-insemination on pregnancy rates and serum progesterone concentrations in dairy cows during different seasons. J. Anim Sci. 81: Suppl.1, p 178. Tsuruta, S., I. Misztal, and T. Druet. 2003. Comparison of estimation methods for heterogeneous residual variances with random regression models. J. Dairy Sci (Suppl. 1) 86:113. Wildman , C. D., J. W. West, and J. K. Bernard. 2003. Effect of dietary cation-anion difference and crude protein content on milk yield and blood metabolites of lactating dairy cows during hot weather. J. Dairy Sci. 86 (Suppl. 1):216. (Abstr.) Williams, R.J., A.M. Chapa, T.O. Riley, D.O. Pouge, S.T. Willard and T.R. Smith. 2003. The impact of tunnel ventilation cooling and brown mid-rib (BMR) corn silage on heat stress in lactating dairy cows. J. Dairy Science 86 (Suppl. 1): 249 (Abstr. T53; ASAS/ADSA 2003 National Meeting, Phoenix, AZ). Williams, R. Justin, Angelica M. Chapa, Thad O. Riley, Donald E. Pogue, Scott T. Willard and Terry R. Smith. 2004. The impact of tunnel ventilation cooling and BMR corn silage on heat stress in lactating dairy cows. J. Dairy Sci 86 (Suppl 1): Abstr.

Impact Statements

Coat color did not appear to have a strong influence on the response of dairy cows to elevated environmental temperatures as measured by either subcutaneous or vaginal temperatures. The higher rectal temperatures found in dark heifers suggests that selection for white coat color may be useful in mitigating the effects of heat stress in dairy cattle in hot climates.
Sprinkling cows resulted in lower afternoon body temperatures of cows and heifers and improved milk yield.
Cows preferred the full Sand Trap compared to the one-half device. Sand was superior to rice hulls as a bedding material because sand remained in stalls and had lower bacterial counts than rice hull bedding.
Gaining a further understanding of the effects of elevated temperature at the cellular and molecular level of the oocyte is a necessary first step toward developing novel strategies aimed at mitigating the negative effect of heat stress for improving reproduction related to oocyte quality.
The norm reaction model for DO allows inexpensive albeit limited genetic evaluation for fertility under heat stress.
The identification of the specific genes involved in thermotolerance among breeds could lead to novel ways to increase resistance of cattle to heat stress.
Seasonal differences in reproductive hormones and blood metabolites indicate that cows in hot weather exhibited differences in the reproductive cycle, which may reflect effects due to nutritional status. Determining these seasonal effects and the causative factors is necessary to develop procedures to improve reproductive performance.
Nutritional modification with yeast and/or Fibrozyme may help to increase feed intake and partially overcome the effects of appetite depression associated with heat stress.
A relationship between DCAD and protein nutrition appears to exist. Increasing dietary DCAD to 50 meq/100 g DM improved feed intake and yield of milk and decreased urinary urea N excretion. A better understanding of this relationship will result in the ability to supply the protein needs of the lactating cow in a more efficient manner.
Should treatment with GnRH post-breeding prove effective for improving fertility in heat-stressed dairy cows, this practice could be easily implemented by producers at very low cost (less than $5 per cow). Nevertheless, the variable nature of the responses observed to date may preclude its use by producers.
Use of a hormonal supplement improved pregnancy rates of heat stressed dairy cows. The effect occurred in hot weather but not during cool weather, indicating that hormonal therapies may be used to enhance reproductive performance in hot climates.
Tunnel ventilation cooling can be used to mitigate the effects of heat stress on lactating dairy cattle in the southeastern US.
Understanding the basic biology of heat stress in dairy cows is crucial to overcoming its effects. This research contributes to that basic research, and also works to identify management strategies to mitigate the impact of heat stress on dairy reproduction.
Holstein cattle have been selected for increased body size in North America for many years. Cooling efficiency based on cow size may assist producers in selecting animals that will most efficiently cool themselves during periods of heat stress. This may result in a net increase in daily income per cow through more efficient cooling via decreased overhead costs by selecting for cow body types that may cool more effectively.