Duration: 10/01/2007 to 10/01/2012

Administrative Advisor(s):

NIFA Reps:

Non-Technical Summary

Statement of Issues and Justification

The need as indicated by stakeholders.
The Food Animal Integrated Research Symposium (FAIR 95) identified the need to increase efficiencies of producing food from animals as a primary objective for future animal research. One of the key research areas with this objective was to improve scientific understanding of reproductive mechanisms. Since FAIR 95, FAIR 2002 was convened as the second national conclave to establish consensus on animal agriculture research and education priorities for the 21st century. Six goals were established for FAIR 2002, each with its own set of objectives. The first of those goals was to strengthen global competitiveness and develop systems to keep U.S. animal agriculture competitive for the 21st century. Objective 1 of that goal is to enhance production efficiency and economic strategies at the farm and ranch level. To partly achieve this objective, the report indicates that research on different farming systems is needed to achieve efficiencies in reproduction. The NC-1006 committee is a long-standing group that has contributed greatly to the increase in reproductive efficiency of cattle since its inception in the early 1970's. Its long-term goal is methods to increase reproductive efficiency in cattle which has been and continues to be consistent with the recent consensus goals set forth by FAIR 2002.

The importance of the work, and what the consequences are if it is not done.
Estrous synchronization and artificial insemination (AI) are reproductive management tools that have been available to beef and dairy producers for over 30 years. In beef cattle, manipulation of the estrous cycle has the potential to shorten the calving season, increase calf uniformity, and enhance the possibilities for utilizing AI. Artificial insemination allows producers the opportunity to infuse superior genetics into their operations at costs far below the cost of purchasing a herd sire of similar standards. These tools remain the most important and widely applicable assisted reproductive technologies available for beef cattle operations. Initial programs failed to address the primary obstacle in synchronization of estrous, which was to overcome puberty or postpartum anestrus. Current research has focused on the development of methods that effectively synchronize estrous in postpartum beef cows and replacement beef heifers by decreasing the period of time over which estrous detection is required, thus facilitating the use of timed artificial insemination (TAI). This new generation of estrous synchronization protocols uses two strategies which are key factors for implementation by producers because they: 1) minimize the number and frequency of handling cattle through a cattle-handling facility; and 2) eliminate detection of estrus by employing TAI. Results from this new generation of work should enhance the use of AI in beef cattle.

Unless owners of commercial cow herds aggressively implement genetic improvement through reproductive management, the U.S. will lose its competitive advantage in high quality beef production. International players that are more technically astute and competitively advantaged will position themselves to dominate the production and sale of beef worldwide.

Aggressive improvement in AI service rate in lactating dairy cows comprises three strategies that can be implemented early during the AI breeding period: 1) submit all cows for first postpartum AI service at the end of the voluntary waiting period (VWP) rather than waiting for cows to express estrus, 2) identify nonpregnant cows early after AI, and 3) aggressively return cows failing to conceive to first AI service to second and subsequent AI services. Traditionally, dairy managers had to rely on visual detection of estrous behavior, which is inefficient due to poor detection and expression of estrous behavior, to submit their cows for AI. The development of Ovsynch, a hormonal protocol that synchronizes follicular development, luteal regression, and ovulation thereby allowing for TAI without the need to detect estrus has radically changed reproductive management by providing dairy managers a practical and effective tool for improving AI service rate. Subsequent modifications of the Ovsynch protocol including presynchronization (i.e., Presynch), which involves two injections of PGF2± administered 14 d apart with the second PGF2± injection administered 12 to 14 d before initiation of Ovsynch and increases conception rate to TAI by 10 to 12 percentage points compared with Ovsynch alone. Refinement and improvement of systematic synchronization systems for submitting cows for first postpartum AI may further improve reproductive efficiency in lactating dairy cows.

In dairy cattle, research has demonstrated that anovulation is an increasing problem in lactating dairy cows. For example, in previous joint research on lactating dairy cows by the NC-1006 committee, we found greater than 26% of lactating dairy cows were anovulatory near the end of the voluntary waiting period. Recent studies by NC-1006 researchers that were discussed at our most recent technical committee meeting have continued to confirm a similarly high percentage of anovulatory cows based on multiple blood samples and multiple ultrasound evaluations of the ovaries. Thus, it seems clear that anovulation is a more significant problem in lactating dairy cows. Modifying the Ovsynch protocol to synchronize the time of ovulation in lactating cows may substantially further reduce labor inputs for reproductive management; however, it may be possible to improve fertility with this treatment (one of the purposes of the current proposal).

Although use of Presynch/Ovsynch and TAI for improving service rate to first AI reduces the impact of poor detection and expression of estrus, systematic strategies to identify and resynchronize nonpregnant cows (i.e., Resynch) are only beginning to be developed and evaluated. Because conception rates of high producing lactating dairy cows average 40 % or less, 60 % or more of cows that receive TAI fail to conceive and, therefore, require a resynchronization strategy to aggressively initiate subsequent AI services. Coupling a nonpregnancy diagnosis with a management strategy to rapidly reinitiate AI improves reproductive efficiency by decreasing the interval between AI services, thereby increasing AI service rate. Development of management strategies to identify and resynchronize cows failing to conceive to TAI is a critical step toward improving reproduction in lactating dairy cows.

The technical feasibility of the research.
During the last 15 years, the NC-1006 project has contributed greatly to the development of several breeding programs to maximize pregnancy rates. These successes directly address the objections or reasons given by cow-calf producers for not adopting reproductive technologies. Information accrued by our group led to the development of the Ovsynch protocol and its variations (i.e., the Cosynch protocol, progestins + the Ovsynch protocol) used in beef cattle. These protocols generally increased pregnancy rates beyond controls because in both dairy and beef cattle, they induce fertile estrus and ovulation in postpartum cows that have not resumed estrous cycles by the end of the volunteer waiting period (dairy cows) or at the onset of the breeding season (beef cows). In the last 8 years, we tested the efficacy of adding progesterone to the Ovsynch protocol in lactating dairy cows. This experiment was replicated at seven (IL, KS, IN, OH, MI, MO, and WI) of the experiment stations involved in NC-1006. In beef cattle, the experiment was replicated at four (IL, KS, MN, and MO) of the stations. All of the above studies have been published in refereed journal publications.

More recently (our current projects), two additional studies have been completed in dairy (six stations) and beef (three stations) that are in the process of data summarization and publication. Therefore, the NC-1006 group has demonstrated the capability to coordinate, conduct, and publish experiments designed to improve fertility in dairy and beef cattle.

The advantages for doing the work as a multistate effort.
Our past three NC-1006 projects have received considerable national attention and acceptance by producers, and it is the aim of the current project to improve fertility and ease of adoption of the tested developments. The multi-state collaborations planned in this project will provide new information applicable to beef and dairy producers and additional stakeholders. A strength of the multi-state collaborations is that they increase the power of the results and demonstrate national applicability. In addition, individual members of the NC-1006 have additional strengths and available laboratory expertise that strengthen our collaborations.

What the likely impacts will be from successfully completing the work.
Beef producers have been slow to adopt these technologies into their production systems. Several factors, especially during early development of estrous synchronization programs, may have contributed to the poor adoption rates. Additionally, these programs failed to manage follicular waves, resulting in more days during the synchronized period in which detection of estrus was necessary. This ultimately precluded fixed-time AI with acceptable pregnancy rates. More recent developments focused on both corpus luteum and follicle control in convenient and economical protocols to synchronize ovulation. These developments will facilitate fixed-time AI use, and should result in increased adoption of these important management practices.

In dairy cattle, it seems clear that anovulation is a more significant problem in lactating dairy cows. Modifying the reproductive management protocols to synchronize the time of ovulation in lactating cows may substantially further reduce labor inputs for reproductive management; however, it may be possible to improve fertility. Development of resynchronization strategies to submit cows failing to conceive to first postpartum AI will further improve reproduction in lactating dairy cows.


JUSTIFICATION

Reproductive inefficiency is one of the most costly and production-limiting problems facing both the dairy and cow-calf industries. For example, in six midwestern states that comprise the Heart of America Dairy Herd Improvement Association, 17.4 % of the dairy cows were culled because of reproductive failure. It was only exceeded by death (18.2 %) as the leading cause of culling (Heart of America Annual DHIA Summary). Similar statistics are reported by other DHIA organizations in the U.S.

Cull beef cow sales makeup 15 to 20 % of cow-calf herd total income (NAHMS, 1997). Over 27 % of beef cows are culled because of reproductive failure or reproductive problems. Based on numbers of operations, that percentage is 34 % of all cull cows. Further, these percentages increase with herd size: < 50 cows (16 %), 50 to 99 cows (30 %), 100 to 299 cows (51%), and > 300 cows (69 %). Only the western region (46 %) has greater culling for reproductive failure than the north-central region (37 %). The NAHMS survey concluded that "by optimizing reproductive performance, producers can decrease forced culls" (i.e., cows sold for involuntary reasons).

Losses that occur because of reproductive failure are partly due to mismanagement of resources and the lack of adoption of appropriate technologies to sustain greater reproductive efficiencies. In the 1997 NAHMS survey of beef cattle producers, questions were posed regarding use of various reproductive technologies on ranches. Of the 1,190 producers surveyed, AI was used by only 13.3 % of the operations; pregnancy palpation by only 34.5 %; and estrus synchronization by 11.9 % of operations. Of interest to our NC-113 committee's long-term objectives were the reasons why estrus synchronization was not employed on those cow-calf operations surveyed. Their reasons were: "it doesnt work" (2 %), "time and labor issues" (36 %), "lack appropriate facilities" (8 %), "cost" (13 %), "too complicated" (20 %), and "other" reasons (21 %). It was likewise interesting that those similar reasons were given, almost to the percentage point, for why those operations had not adopted the use of AI. Therefore, it is imperative to continue developing mechanisms to enhance reproductive efficiency in cattle, through basic and applied research outlined in current objectives.

The long-term goal of this proposal is to develop methods to increase reproductive efficiency in cattle. This Specific Aim long-term goal will be addressed through the two Objectives below.

Related, Current and Previous Work

Related Regional Projects


The NE-1007 (formerly NE-161) committee is addressing parallel work, but their focus is a broad overview addressing factors related to embryonic or fetal survival in cattle. They are addressing multiple events and mechanisms associated with follicular growth and maturation, corpus luteum formation and development that may result in embryonic or fetal loss. Additional objectives of NE-1007 are to focus on potential environmental and metabolic factors that are related to embryonic survival. The W-1112 (formerly W-112) committee also addresses parallel work, but their focus addresses a range of physiological and endocrine systems related to reproduction in multiple species. Their focus is more basic in nature in an effort to discover underlying mechanisms associated with reproduction. They are addressing basic physiological, immunological, metabolic, and genetic systems that may be utilized for further development of reproductive management systems. The objectives of our NC-1006 project are more specifically related to manipulation of reproductive management systems and to understand the underlying mechanisms that responsible for the success of those systems.


Dairy Cattle


Pregnancy rate in high-producing lactating dairy cows are less than desired. Pregnancy rates per AI have decreased from 66% in 1951, to about 50% in 1975, to less than 40% today (Butler and Smith., 1989; Pursley et al., 1997a,b; Stevenson et al., 2006). Pregnancy rate per AI in heifers, however, is about 60% (Kuhn et al., 2006). Decrease in conception rates in lactating dairy cows is most likely related to the dramatic increase in milk production per cow during the same period (Oltenacu et al., 1980; Nebel and McGilliard, 1993). The mechanism by which milk production might decrease fertility is unknown.
One possible mechanism for decreased fertility is changes in circulating reproductive hormone concentrations particularly progesterone. Studies indicate that reduced progesterone concentrations before AI result in poor fertility. Characterization studies (Fonseca et al., 1983; Rosenberg et al., 1990; Folman et al., 1990) have indicated a strong correlation between plasma concentrations of progesterone during the luteal phase before AI and subsequent conception rates. For example, Fonseca et al. (1983) showed an average of a 12.4% decrease in conception rate related for every 1 ng/mL decrease in progesterone concentration during the last half of the estrous cycle preceding first service. These studies clearly identified physiologic differences in cows of varying fertility, but did not define the mechanism underlying the difference.


A number of recent manipulative studies (Sirois and Fortune, 1990; Kinder et al., 1996; Savio et al., 1993; NE-161, 1996) used various methods to produce reduced plasma progestin concentrations and found aberrant growth of the dominant follicle. Reduced progesterone concentrations facilitate extended growth of a dominant follicle producing what is termed to be a persistent follicle. It is clear that conditions that produce a persistent follicle result in poor fertility (Sanchez et al., 1993; Savio et al., 1993; Wehrman et al., 1993; Kinder et al., 1996; NE-161, 1996). For example, in a publication by the NE-161 project, development of a persistent follicle resulted in reduced pregnancy rate from 54% to 15% in lactating dairy cows (NE-161, 1996). It is likely that the decrease in fertility was a direct effect of increased LH pulsatility causing premature activation of the oocyte (Revah and Butler, 1996). A uterine effect, however, cannot be discounted, because Shaham-Albalancy et al. (1997) provided evidence that elevated progesterone during the estrous cycle may depress uterine secretion of PGFM and alter uterine endometrial morphology during the subsequent estrous cycle.
Progesterone supplementation of dairy cows for 7 days before a second injection of PGF2a increased pregnancy rates compared with non-supplemented controls (Folman et al., 1990; Wehrman et al., 1993). In addition, elevated endogenous concentrations of progesterone produced by a corpus luteum increased pregnancy rates after synchronization of estrus with norgestomet (Sanchez et al, 1993). A well-controlled experiment using a large number of dairy cows in New Zealand found a slightly reduced pregnancy rate after PGF2a treatment (Xu et al., 1996). Reduction in pregnancy rate resulted from poorer pregnancy rates in cows inseminated after regression of a new corpus luteum (days 5 to 8 of the estrous cycle) such that the ovulatory follicle matured in a reduced progesterone environment (Xu et al., 1996). Supplementation with progesterone using a controlled internal drug releasing device (CIDR) for 5 days before the PGF2a treatment restored normal pregnancy rates in cows in this early luteal phase (Xu et al., 1996). In contrast, Smith and Stevenson (1995) observed similar conception rates in lactating cows and virgin heifers when either the PRID or a progestin (norgestomet) implant was used in a similar design, but only in cows that had a functional corpus luteum during progestin treatment. In cows without a corpus luteum, conception rates were less than controls; and particularly less after norgestomet than after PRID treatment. Norgestomet implants produce a reduced concentration of progestin and at least 2 implants are required to reduce LH pulsatility to those observed during mid-luteal phase (Sanchez et al., 1995). Our first proposed project will use a CIDR containing progesterone to increase serum progesterone concentrations and evaluate the effect on pregnancy rate during Ovsynch, which was developed as part of our previous NC-113 project.
When GnRH was administered at random stages of the estrous cycle, the dominant follicle in 83% of lactating dairy cows and 45% of heifers ovulated with subsequent initiation of a new follicular wave (Pursley et al., 1995). When PGF2a was given 7 days after GnRH, luteolysis occurred and the dominant follicle arising from a new wave of follicles that emerged after GnRH was capable of ovulation in response to a second GnRH injection given 48 h after PGF2a (Pursley et al., 1995). This treatment (GnRH + PGF2a + GnRH + timed AI), known as Ovsynch, has been adopted by many dairy producers as a method for programmed AI-breeding. Pregnancy rates resulting from such a treatment were similar to those achieved in lactating dairy cows inseminated after a detected estrus (Pursley et al., 1997a, NC-113 joint project; Pursley et al., 1997b). In contrast, pregnancy rates were less in heifers after Ovsynch and timed AI compared with those after detected estrus, as would be expected from the poor synchronization rates achieved with this protocol in heifers (Pursley et al., 1995; Pursley et al., 1997a, NC-113 joint project). Using this treatment, pregnancy rates in 2 other studies (Stevenson et al., 1996; Burke et al., 1996) were less than those in cows inseminated at estrus, but overall pregnancy rates (proportion of cows assigned to treatment that conceived) were similar. The improvement in service rate and the elimination of dependence on detection of estrus (reduced labor and errors) have made this protocol attractive to dairy producers in spite of the lack of improvement in pregnancy rate.


In our more recent NC-113 joint project (Stevenson et al., 2006), there was variation in pregnancy rates, percentage cycling, and average days in milk (DIM) among stations. Noncycling cows treated with Ovsynch + CIDR, but failing to ovulate after the first GnRH injection of Ovsynch, however, had greater overall pregnancy rates on day 28 after TAI than similarly treated noncycling cows that received Ovsynch, but no CIDR. In addition, at 4 of 6 locations, pregnancy outcome 28 days after TAI were improved in response to progesterone, whereas at 56 days after TAI, outcomes were improved in at 3 of 6 locations. Pregnancy losses between 28 and 56 days of pregnancy were greater in noncycling than cycling cows, and was associated with improved pregnancy outcomes.


Our most recent NC-1006 joint project was designed to determine whether noncycling dairy cows could: 1) be identified accurately by use of a heatmount detection patch (Kamar); 2) beidentified accurately by 1 (10 days before timed AI or TAI) or 2 (3 and 10 days before TAI) ultrasonographic exams; 3) have improved pregnancy rates by insertion of a CIDR in conjunction with an Presynch + Ovsynch ovulation-synchronization breeding protocol; 4) have improved pregnancy rates by altering timing of AI to occur concurrent with GnRH or 24 h after GnRH injection; and 5) have reduced pregnancy loss by previous exposure to the CIDR or altered timing of TAI. In addition, we tested whether pregnancy rates and pregnancy loss of cycling dairy cows were improved by altering timing of AI to occur concurrent with GnRH or 24 h after GnRH injection. Preliminary results have established that in lactating dairy cows, Kamar patches in place during 4 wk before initiating a TAI protocol (Ovsynch) overestimated previous estrual activity in cows subsequently classified as anestrus. Kamars overestimated previous estrual activity compared with 1 ultrasound exam conducted before the first GnRH injection of Ovsynch. Kamars slightly underestimated previous estrual activity in cows later classified as cycling. Fertility (pregnancy rate or pregnancy loss) was not improved significantly by addition of the CIDR insert to cows identified as anestrus. Cows previously identified as anestrus, however, had reduced pregnancy rates at days 33 and 61 (regardless of whether they received a CIDR insert) compared with control cows classified as cycling.


Beef Cattle


Estrus-synchronization programs in beef cattle are designed to reduce the breeding season, increase weaning weights, and group cows and heifers so AI can be used more efficiently (Odde, 1990). Treatments involving single (Fonseca et al., 1980; Kesler et al., 1980) or multiple injections of GnRH (Edwards et al., 1983; Short et al., 1990), norgestomet implants (Ramirez-Godinez et al., 1981; Troxel et al., 1993), and(or) feeding melengestrol acetate (Patterson et al., 1989), with or without temporary calf removal, were used to induce ovulation and(or) estrus in cycling or anestrous suckled cows. Norgestomet prevented the short estrous cycle that normally follows first pubertal ovulations in heifers (Gonzalez-Padilla et al., 1975). Short estrous cycles in suckled cows that follow early weaning (Ramirez-Godinez et al, 1981) or ovulation induced by GnRH (Troxel and Kesler, 1984) or hCG (Garcia-Winder et al, 1986) are also prevented by pre-gonadotropin or gonadoreline treatment with norgestomet. The first short estrous cycle in suckled cows prevented the continuation of pregnancy when fertilization occurred (Ramirez-Godinez et al., 1982).


Various treatment procedures developed to either induce or synchronize ovulation in anestrous and estrus-cycling suckled cows by administering GnRH and PGF2a, with (Troxel et al., 1993; Hoffman et al., 1996) and without a progestin source (Twagiramungu et al., 1995), have resulted in pregnancy rates that exceeded controls. Use of Ovsynch in suckled beef cows with fixed-time AI at the time of the second GnRH injection (48 h after PGF2a) or 24 h after the second GnRH injection has produced promising results (Geary et al., 2001; Stevenson et al., 2000). Similar treatments (GnRH + norgestomet + PGF2a or GnRH + PGF2a) in suckled beef cows resulted in rates of detected estrus and pregnancy that exceeded controls given 2 injections of PGF2a (Stevenson et al., 2000). These Ovsynch or Ovsynch-like treatments induce estrus and subsequent pregnancy rates equal to those of estrus-cycling cows inseminated after a detected estrus regardless of whether AI occurred was after detected estrus or after one TAI.


In our NC-113 joint project (Lamb et al., 2001), we compared Cosynch to a treatment in which progesterone (CIDR) was added between the first injection of GnRH and the injection of PGF2a. Pregnancy rates were greater for Cosynch + progesterone (58%) than for Cosynch-treated (48%) cows. Cows that had follicles >12 mm on day 2 had greater pregnancy rates than those having follicles £ 12 mm regardless of treatment. Pregnancy rates were similar between Cosynch and Cosynch + progesterone treatments when cycling cows had elevated concentrations of progesterone at day 0 (day of PGF2a injection), but pregnancy rates were greater in the Cosynch + progesterone (79%) than in the Cosynch (43%) treatment when cycling cows had reduced concentrations of progesterone on day 0. Similarly, among noncycling cows, pregnancy rates were greater in the Cosynch + progesterone (59%) treatment than in the Cosynch (39%) treatment. We concluded that treatment of suckled cows with Cosynch yielded acceptable pregnancy rates, but addition of a CIDR improved pregnancy rates in noncycling cows. Body condition and days postpartum at initiation of the breeding season affected overall efficacy of the Cosynch and Cosynch + progesterone protocols.


Several researchers from the NC-1006 project implemented and coordinated a multi-state, multi-location experiment to determine whether the CO-Synch + CIDR protocol could yield pregnancy rates similar to protocols requiring detection of estrus (Larson et al., 2006). Results demonstrated that the CO-Synch + CIDR protocol yielded fertility similar to the estrus-detection protocol (Select Synch + CIDR, plus a clean-up TAI at 84 hr) with the greatest pregnancy rates (54 vs. 58%, respectively). In addition, these pregnancy rates were achieved despite of 35% of cows in anestrus at the onset of the estrus-synchronization protocol.


Our most recent NC-1006 joint project determined whether resynchronization of an ovulatory estrus could be accomplished in nonpregnant cows without compromising pregnancy in cows pregnant from a previous synchronized estrus or to those inseminated to the resynchronized estrus. Our results indicated that resynchronization with a CIDR after a TAI did not seem to alter TAI or overall pregnancy rates, or affect embryo survival. Cows resynchronized with a CIDR between 14 and 21 or 5 and 21 days after TAI, however, had greater synchrony of estrus than controls or cows resynchronized between days 5 and 14 after TAI, but conception rates of cows receiving a CIDR until 21 days after TAI was poorer than controls or those cows receiving a CIDR until 14 days after TAI.
Development of a TAI protocol in beef heifers has not been as straightforward as the development of TAI system for cows, especially considering that at the onset of the estrus-synchronization protocol, a majority (greater than 85%) of heifers have attained puberty (Lamb et al., 2006). The primary reason for TAI system failure in heifers seems to be the inability to synchronize follicular waves with the same precision as that achieved in cows. After an injection of GnRH at random stages of the estrous cycle, 75 to 90% of postpartum beef and dairy cows ovulated a follicle after an injection of GnRH at random stages of the estrous cycle (Pursley et al., 1995; Thompson et al., 1999; El-Zarkouny et al., 2000), whereas only 48 to 60% of beef and dairy heifers ovulated follicles in response to the same treatment (Macmillan and Thatcher, 1991; Pursley et al., 1995; Moreira et al., 2000). We reported no difference in synchrony of estrus or pregnancy rate between CIDR + PGF2a and Select Synch + CIDR treated heifers, suggesting that because of the poor response to GnRH in heifers at CIDR insertion, using GnRH may be of limited value (Lamb et al., 2006).


Recently, Atkins and Smith (2005) evaluated follicular response to GnRH among pubertal beef heifers on specific days of the estrous cycle. Response was based on ovulation or luteinization of a dominant follicle and subsequent initiation of a new follicular wave in response to GnRH. Heifers receiving GnRH on days 2, 10, and 18 failed to ovulate more than 70% of dominant follicles, whereas heifers receiving GnRH on ay 5 successfully ovulated in 92% of those treated.


In a large, multi-location (12 locations) study using GnRH, PGF2a, and CIDR, researchers from the NC-1006 project (Lamb et al., 2006b) tested the hypothesis that GnRH at CIDR insertion would not enhance pregnancy rates and a TAI protocol would yield pregnancy rates similar to protocols using detection of estrus. Results revealed that GnRH did not enhance pregnancy rates and the CO-Synch + CIDR protocol yielded similar pregnancy rates to the Select Synch + CIDR or CIDR-PG that utilize detection of estrus. Nevertheless, a bewildering fact remains that the average pregnancy rates for these protocols ranges between 53 and 58%, whereas other studies have reported pregnancy rates using MGA or a long-term CIDR to range between 60 and 75% (Lamb et al., 2000, 2004, 2006; Larson et al., 2006; Patterson et al. 2003; Kojima et al., 2004).


Further research is required to understand methods to control the estrous cycle in heifers that will facilitate effective estrus-synchronization protocols for beef heifers.


Because the collection of binomial data (pregnancy rates) requires large sample sizes to adequately test hypotheses, the NC-1006 (formerly the NC-113) group has collaborated well to provide results to be used in a typical production setting. Our future NC-1006 projects will continue to include a high degree of collaboration among stations to ensure that our objectives are met and provide meaningful results for use by the dairy and beef cattle industries.

Objectives

1. To elucidate mechanisms regulating reproductive efficiency in cattle.
   
2. To develop reliable, efficient, and economical breeding protocols for cattle.
   

Methods

Objective 1. To elucidate mechanisms regulating reproductive efficiency in cattle. Assessment of Nutrition Reproduction Interactions of Beef Females (NE, SD) Fetal programming is the term used to describe the idea that a maternal stimulus or insult at a sensitive period of fetal development could have long term effects on the fetus or new born. Recent research by current NC-1006 members has compared steer calf performance from dams either receiving crude protein supplementation during the last third of gestation or receiving no supplementation. Calves from supplemented dams are heavier at weaning and tend to reach heavier carcass endpoints. Preliminary results also indicate that heifers from supplemented dams have greater first-service conception rates and greater overall pregnancy rates. Steer and heifer performance results indicate fetal programming may be occurring. We will determine the effect of late gestation nutrition on subsequent growth and reproductive performance in heifer calves. Late gestating cows will either graze on winter range or cornstalks with or without protein supplementation. Subsequent growth and reproductive performance of heifer calves will be evaluated. Dried distillers grains (DDG) are a by-product of ethanol production that provide approximately 120% of the energy value of corn for cattle on forage diets. Therefore, DDG are a logical and sustainable option for short-term supplementation of heifers developed on range. Alternative programs for developing heifers must reduce cost and economic risk to improve the sustainability of ranches in the North Central region. Multi-location projects (NC-1006 members) using beef heifers on cooperating ranches are planned to evaluate reproductive performance of heifers developed on range and supplemented with dried distillers grains for 1 wk before and 18 days following AI or natural service. Growth, synchronization rate, AI-pregnancy rate, and overall pregnancy rate will be monitored to evaluate treatment effects. Post-insemination nutrition may influence embryonic survival through many mechanisms: changes to the uterine environment, uterine secretions, or by influencing the concentrations of progesterone. We will determine whether post-AI changes in nutrition can influence reproductive efficiency in beef heifers. We will determine how changes in nutrition (moving from a feedlot to pasture) following insemination can influence the uterine environment and pregnancy rates. We will utilize estrous-synchronization protocols and measure post-insemination nutritional metabolites, uterine changes in pH changes, and monitor diet alterations. Heifer calves will be weighed at birth and weaning, and fed individually in Calen gates to determine feed efficiency from weaning until the onset of the breeding season. Blood samples will be collected bi-weekly to determine age of puberty and cycling status before the breeding season. Effect of supplementation before and through maternal recognition of pregnancy on first-service pregnancy rates will be measured. We will determine how preovulatory concentrations of estradiol related to standing estrus regulate uterine environment at time of AI, and how uterine environment at time of AI can influence sperm motility and fertility. Mechanisms Associated with Decreased Reproductive Efficiency High-Producing Dairy Cows (KY, IA) We will conduct an experiment designed to examine the effects of physiological status (heifers, dry cows, and lactating cows) on the concentrations of progesterone maintained by CIDR inserts. Preliminary results indicate that CIDR inserts were able to maintain approximately 1 ng/mL of progesterone in lactating cows, about 2 ng/mL in dry cows, and almost 3 ng/mL in heifers. In the second replicate, we intend to relate these concentrations to body weight, dry matter intake and milk production (lactating cows only). In addition, we will determine if the reduction in duration in estrus expression seen in high-producing dairy cows is related to a reduction in peripheral concentrations of estradiol. Both the reduced concentrations of progesterone in lactating cows in the first experiment, and the potentially reduced concentrations of estradiol that we expect to see in the second experiment may be due to the enhanced metabolic clearance of steroid hormones recently demonstrated in lactating cows. Preliminary results indicate that peroxisome proliferator-activated receptor (PPAR) ³ is expressed in both follicular and luteal tissue in cattle, which are mediators of dietary regulation of gene expression. Various metabolic and nutritional agents, such as fatty acids and prostaglandins, activate the PPARs. We hypothesize that PPARs can directly impact ovarian function by regulating follicular and luteal gene expression. To determine the role of PPAR³ in the oocyte, agonists, and an antagonist of PPAR³ will be added to maturation media and their effect on oocyte maturation investigated. In addition, sperm will be added to in vitro matured oocytes in the presence of PPAR³ agonists and an antagonist to determine how activation/inhibition of this transcription factor impacts the development of an 8-cell blastocyst. It is anticipated that activation of PPAR³ in immature oocytes will delay maturation, whereas its activation in mature oocytes will enhance early blastocyst development. Basic Mechanisms Associated with Oocyte Quality and Ovarian Structures (IN, NE, OH, SD) Researchers are currently examining the mechanisms of oocyte quality using genomic and proteomic approaches. Currently, we are identifying and validating target genes, as well as differences in protein complement, that are related to developmental competence. We will then examine the expression of specific genes and the presence of targeted proteins during different manipulations of the reproductive cycle in relation to in vitro oocyte maturation, fertilization, and embryo developmental success, as well as embryonic loss and pregnancy rates. This approach will allow us to determine the mechanisms that are involved in oocyte quality, and how manipulations of the reproductive cycle impact the ability of the resultant ovulated oocyte to produce a viable embryo, fetus and offspring. When differentially expressed gene transcripts and proteins related to oocyte quality have been identified, effective strategies can be developed to alter specific pathways critical to developmental potential of oocytes. This research will enable the development of synchronization and superovulation protocols to maximize oocyte competence and thus increase pregnancy rate. The heritability of age at puberty in beef heifers is 0.52 and closely linked to growth traits. In addition, oocyte quality improves with advancing age. Recently, a clock gene, Period (Per1), was express in the bovine oocyte (Cushman et al., 2007). Clock genes are transcription factors that represent a key link between metabolic status and fertility, and may be a key regulatory point between growth-metabolic pathways and fertility in cattle. Therefore, clock gene mRNA expression in peripheral tissues (adipose and blood) may be an effective biomarker of postpartum interval to ovulation, ovulatory capability, and oocyte competence in pubertal heifers and postpartum cows. Blood will be collected from cows during an estrus-synchronization protocol mixed with 0.25 mL of Trizol and frozen. Total cellular RNA will be extracted, DNAse treated and subjected to real-time RT-PCR for Per1 using an established assay. Relative levels of Per1 mRNA corrected for GAPDH (or another appropriate house-keeping gene) will be compared in a model that includes cyclic status, age, Julian day of the year, and pregnancy outcome. In addition, 40 postpartum cows (3 yr of age) will be subjected to tail-head adipose biopsy during the first week after calving, and adipose samples will frozen in liquid nitrogen. At biopsy, a blood sample will be collected and body condition scores will be evaluated. Cows will be checked daily for estrus, and 7 to 10 days after first estrus, a second adipose biopsy will be collected. At this time, ovaries will be subjected to ultrasound scan to count CL and follicles and a blood sample will be taken. Any cows that have not cycled by May 23 will be scheduled for their second biopsy at that time. The Per1 mRNA expression in adipose and blood samples will be evaluated in a repeated measures model that includes Julian day, cyclic status, and pregnancy outcome. The precise mechanism of action of PGF2± to cause luteal regression remains elusive. The initial obligatory events triggered by PGF2± that result in irreversible loss of steroidogenic function and structural degeneration of the tissue have not yet been clarified. We will determine whether PGF2± affects the concentrations of mRNA for various functional proteins [e.g., vitamin C transporters 1 and 2, vascular endothelial growth factor A (VEGFA), receptors for VEGFA] in sheep corpora lutea. We intend to examine the acute (within 2 h) vs. chronic (within 24 h) effects of PGF2± on gene expression in CL that have not (early CL) or have (later CL) acquired luteolytic capacity. Total RNA will be isolated from each CL, purified, and verified for integrity. Real-time PCR will be used for relative quantification of mRNA of a variety of functional proteins. Real-time methods will be optimized and validated using at least 1 endogenous reference gene, such as ²-actin or L-19. Quantity of the mRNA of interest that is present in each sample will be expressed as fold change from the mean value for the control CL collected during the early luteal phase. Data will be analyzed using analysis of variance for a split plot design with ewe as the main plot and CL as the subplot. Efficient transportation of sperm through the female reproductive tract requires that the female be in estrus or under the influence of estrogen. Fertilization failure in lactating beef cows ranged from 0 to 25% and in lactating dairy cows from 12 to 45%. Estrogen may influence fertilization rates through both sperm transport and fertilization efficiency by altering the uterine environment around the time of fertilization. We will assess how preovulatory concentrations of estradiol and the uterine environment at time of insemination can influence fertility. Objective 2. To develop reliable, efficient, and economical breeding protocols for cattle. Protocols for Dairy Cattle (KS, IL, MN, WI) Collaborative studies will be done to test various post-insemination treatments designed to improve conception rates and pregnancy survival in lactating dairy cattle. Treatments will include single and combinations of gonadorelins, gonadotropins, and progesterone (CIDR insert) applied at strategic points after insemination to induce ancillary luteal structures, increased progesterone, or both, in addition to improved fertility. A presynchronization strategy in which two injections of PGF2± are administered 14 d apart with the second PGF2± injection administered 12 to 14 d before initiation of Ovsynch (i.e., Presynch) increases fertility to TAI in cycling lactating dairy cows compared with Ovsynch alone. We will evaluate various treatments to presynchronize estrous cycles in lactating dairy cattle before applying a timed AI (TAI) protocol. Treatments will include single and combinations of GnRH, PGF2a, and progesterone (CIDR inserts) applied to cows to ensure they are between days 5 and 12 of the cycle when a TAI protocol is initiated. An untested strategy to resolve the anovular condition before TAI is to incorporate GnRH into a presynchronization strategy to induce ovulation of a follicle and increase endogenous progesterone production from the newly formed corpus luteum to resolve the anovular condition before cows initiate Ovsynch, thereby increasing fertility to TAI and reducing subsequent pregnancy loss. One strategy to optimize fertility to Resynch and TAI has been to determine the optimal interval after TAI to initiate Resynch based on assumptions regarding the physiology of the estrous cycle. Assuming an estrous cycle duration of 21 to 23 d, initiation of Resynch 32 to 33 d after TAI should ensure that the first GnRH injection of Resynch occurs between Day 5 to 12 of the estrous cycle, a stage of the cycle when a CL should be present and that results in greater fertility when Ovsynch is initiated. Despite this logic, 16% to 22% of cows lack a CL 33 d after TAI suggesting that there is significant variation among a group of cows at various times after synchronization using Presynch + Ovsynch and TAI. An alternative approach that will be tested is to presynchronize cows before initiation of Resynch using a variety of hormonal strategeies involving single treatments of combinations of treatments with GnRH PGF2a, and/or progesterone. Protocols for Beef Cattle (KS, IL, MN, NE, SD) Studies will focus on the development of protocols to synchronize the return estrus (resynchronization) of cows not conceiving to the first timed AI protocol. Tools that will be used for resynchronization include the CIDR and GnRH; 2 products that are currently available to veterinarians and producers. Concurrently, methods of early pregnancy detection will be evaluated. Tools that will be used for early pregnancy status will include progesterone, interferon-tau, and interferon-induced products. The objective is to develop a program that will include a primary synchronization program that will consistently achieve 60% pregnancy rates, a resynchronization program that will allow for treatment regardless of pregnancy status to the first timed AI so that 2 attempts can be made to establish pregnancy in each and every cow within 23 days of the first timed AI. Studies will be done in successive years based on results of previous years. Highly effective synchronization programs (before first insemination) are already established. Cows synchronized with these primary synchronization protocols will be used for the resynchronization and pregnancy determination studies. Resynchronization protocols used in conjunction with the primary synchronization will be evaluated by assessing pregnancy rates to second and cumulative (first and second) insemination (or embryo transfer). Success of early pregnancy detection determinations will be assessed retrospectively by examining for pregnancy via ultrasound examination. Once a complete program is established the complete protocol will be evaluated at multiple locations. We will focus on the development of a TAI ovulation-synchronization protocol for beef heifers. The first goal will be addressed by focusing on assessment and characterization of follicular dynamics in heifers treated at different stages of the estrous cycle with either GnRH or either of 2 doses of hCG (500 and 1,000 IU). Ovulation and emergence of a new follicular wave after administration of GnRH or hCG are of critical importance. In addition, interval after GnRH or hCG administration to follicle dominance and atresia will be assessed before initiation of goal 2. The second goal is based on the desirable dose of hCG and assessment of the approximate interval from hCG to PGF administration from goal 1, we will evaluate the timing of ovulation after PGF in pubertal and peripubertal beef heifers with or without exogenous progesterone (CIDR) between hCG and PGF2a administration. The third goal will be to determine the optimal timing of either hCG or GnRH administration and AI following administration of the best protocol identified in goal 2 to maximize conception rate to fixed-time AI.

Measurement of Progress and Results

Outputs

• Research associated with nutrition reproduction interactions of beef females will be completed and provided in research publications.
• Results acquired from research focusing on mechanisms associated with high-producing dairy cows will be published.
• Basic mechanisms associated with oocyte quality and ovarian structures will be researched and findings will be presented in published form.
• Presynchronization, synchronization, and resynchronization protocols will be developed and presented in published form.
• Fixed-time artificial insemination protocols in beef heifers and cows will be published.
• Output 6;All research data will be published in experiment station reports, abstracts, refereed journal articles, and otherwise presented at professional meetings for animal scientists and industry professionals.

Outcomes or Projected Impacts

• Data generated will indicate specific nutritional, physiological, and molecular factors that are related to beef and dairy cattle fertility. These results will be used to specifically generate reproductive management protocols that enhance reproductive efficiency in beef and dairy operations.
• Refined and development of resynchronization, estrus-synchronization, and resynchronization strategies that enhance fertility and embryonic survival will be developed for dairy cattle.
• Development of a reliable, efficient fixed-time AI protocol for beef heifers and refinement of current fixed-time AI protocols for beef cows.

Milestones

(2008): Initiate discovery of nutritional, physiological, and molecular factors associated with fertility in beef and dairy cattle, plus initiate development or refinement of reproductive management protocols.

(2009): Preliminary reports indicating potential factors associated with fertility in cattle and continue generating data for development of reproductive management protocols.

(2010): Initial summaries on new developments of estrous synchronization, presynchronization, and resynchronization protocols.

(2011): Disseminate findings to scientific community, industry professionals, producers and veterinarians.

(2012): Publication in scientific journals.

Projected Participation

View Appendix E: Participation

Outreach Plan

The Beef Reproductive Task Force is composed of mostly scientists in the North Central region with major extension appointments. Their objectives and mission are to provide leadership and consistency in programming to the beef industry with the following goals: 1) promote wider adoption of reproductive technologies among cow-calf producers; 2) educate cow-calf producers in management considerations that will increase the likelihood of successful AI breeding; and 3) educate producers in marketing options to capture benefits that result from use of improved reproductive technologies. Three specialists in this task force are principle investigators and station representatives of NC-1006. Their efforts have been coordinated and correlated with our project during the last 8 years. This task force has been instrumental in providing the latest developments in reproductive management systems of beef cattle through workshops, publications, and maintaining an active relationship with veterinarians, pharmaceutical and artificial insemination industries.


The Dairy Cattle Reproduction Council (DCRC) is a newly established organization with similar goals to the Beef Reproduction Task Force to provide leadership in terms of educating the dairy industry on critical reproductive management systems. The DCRC leadership includes two specialists that are representatives of NC-1006. The inaugural DCRC convention convened in Denver, CO in November 2006 with over 300 attendees present. Representatives were present from industry groups, bovine practitioners, academia, and dairy producers from across the U.S. and Canada. Data acquired by scientists in NC 1006 will be presented at workshops and in publications to ensure that dairymen have access to the most current reproductive management programs.

Organization/Governance

The technical committee shall consist of 1 officially designated representative from each participating agricultural experiment station. The technical committee will meet annually. CSREES will designate 1 nonvoting representative. Officers will be elected for a period of 1 year, consist of Chairman and Secretary, and will progress from Secretary to Chairman. Elections will be held at the annual meeting. Officers will compose the executive committee. The executive committee, together with administrative advisors, is authorized to function on behalf of the technical committee in all matters pertaining to the regional project requiring interim action.


The Chairman, in consultation with the administrative adviser, shall arrange the time and place of the meeting, notify technical committee members of the meeting site, and prepare the agenda. The Chairman is responsible for preparation of the annual report of the regional project. The Secretary will record and distribute minutes of the annual meeting. Subcommittees may be appointed by the Chairman as needed for specific assignments. The executive committee will be in charge of coordinating cooperative research trials.

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Attachments

Land Grant Participating States/Institutions

FL, IA, IL, IN, KS, KY, ME, MN, MO, MS, ND, NE, OH, SD, WI

Non Land Grant Participating States/Institutions

USDA ARS