Brief Summary of Minutes of Annual Meeting

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.

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.

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.)