NC1201: Methods to Increase Reproductive Efficiency in Cattle

(Multistate Research Project)

Status: Active

NC1201: Methods to Increase Reproductive Efficiency in Cattle

Duration: 10/01/2022 to 09/30/2027

Administrative Advisor(s):

NIFA Reps:

Non-Technical Summary

Statement of Issues and Justification

Need as indicated by stakeholders

Assessments performed by the United Nations estimated that the world population will increase by over a third between 2009 and 2050, likely reaching overall numbers to over 9 billion people (FAO). Over the same period of time, individual average incomes are also expected to increase, as shown by recent trends of growing economies in developing countries (Mensbrugghe et al., 2009). A positive correlation exists between per capita income and demand for animal food products (milk, meat, and eggs; Sans and Combris, 2015). These projections indicate that overall food production will have to increase by 70% and meat production by 42% in order to meet the demands for this growing population. Although considerable increases in food production are needed, land availability for agriculture is estimated to increase only by 5-12% (FAO, 2009).

These projections indicate that our current food production systems will have to undergo considerable changes in order to optimize production efficiency and meet the growing demand for food, while maintaining ecological stewardship and proper use of limited natural resources. Increasing reproductive efficiency of both beef and dairy cattle will contribute to the milk and meat supplies for our future food need and for the U.S. to maintain a competitive advantage in milk and meat products.

Originating more than 40 years ago, this project strives to develop solutions for reproductive inefficiencies in dairy and beef cattle by increasing efficiency and predictability of reproductive programs. This has been accomplished through evaluating mechanisms that regulate reproductive processes that impact production efficiency and disseminating reproductive management information to stakeholders to improve sustainability in both beef and dairy industries.

Importance of the work and what the consequences are if it is not done


Over the last decades several advances in reproductive biotechnologies such as estrus-synchronization and fixed-time artificial insemination (TAI) have helped producers enhance fertility, improve genetic traits of their cattle, tighten the breeding season and shorten the calving season, leading to an increase in overall efficiency of cow-calf production systems. Although significant progress has been made, and the rate of adoption of assisted reproductive technologies (ART) has increased, natural service by itself is still by far the main breeding strategy utilized in beef cow-calf operations. According to a recent USDA report, only 11.6% of the cow-calf operations in the U.S. utilize AI (USDA, 2020), whereas 89.3% of the dairy operations artificially inseminate their cows (NAHMS, 2014). Currently recommended estrus synchronization protocols for TAI in beef herds yield pregnancies rates that normally range between 40-60% (Lamb et al., 2016; Reese et al., 2020). While these results are positive, only approximately half of the calf crop from the few operations that do utilize these strategies are produced via AI, limiting the speed in which superior genetics are spread across the beef industry.

Unless commercial beef producers aggressively implement genetic improvement through the use of reproductive management, the U.S. will lose its competitive advantage to countries such as Brazil and Argentina, which are leading export countries for U.S. beef genetics. For example, according to the Association for Brazilian Artificial Insemination, there was a 285% increase on the proportion of beef cows artificially inseminated between 2002 and 2019 in Brazil. Moreover, data collected by the International Embryo Technology Society indicates that Brazil currently has greater adoption of embryo transfer technology than the U. S.

Multi-state research and extension efforts to maximize the use of reproductive technologies, such as artificial insemination and embryo transfer, are warranted and will contribute to maintaining the genetic advantage of U.S. beef herds compared with other beef producing countries. An important driver of the adoption of ART is the efficiency and predictability of these technologies. Multi-disciplinary basic and applied research to maximize the efficiency and predictability of these technologies will play an important role on the future of the U.S. beef industry.


Over the past two decades, a reproduction revolution has occurred in the dairy industry. Based on data from nearly 20 million inseminations in >23,000 U.S. herds, phenotypic performance for reproductive outcomes in U.S. Holstein and Jersey cows as well as genetic merit for daughter pregnancy rate reversed their historical declines and began to increase in 2002 (Norman et al., 2009). Although many factors are associated with the dramatic increase in reproductive performance (genetics, nutrition, management, etc.), the development of fertility programs (for our review see Carvalho et al., 2018) and their adoption by dairy farmers (Caraviello et al., 2006) has driven much of this change. Fertility programs for TAI as well as strategies for pregnancy diagnosis and resynchronization of ovulation have not only increased the AI service rate, but also have increased pregnancies per artificial insemination (P/AI) in high-producing Holstein cows by about 10-percentage points compared to AI to a detected estrus (Santos et al., 2017).

To compensate for these changing economic conditions, dairy farms have rapidly implemented dairy herd inventory management strategies to right-size replacement heifer inventories and maximize profit. One of the key reproductive technologies they have turned to is sexed semen. Use of sexed semen increases genetic progress in dairy herds through increased dam selection intensity (Khalajzadeh et al., 2012). Other strategies include use of genomic testing or pedigrees to identify genetically superior heifers and cows, use of sexed semen to inseminate genetically superior dairy heifers and lactating cows balanced for replacement needs (Weigel et al., 2012), and use of beef semen to inseminate low genetic merit heifers and cows to produce crossbred bull calves with increased value in the beef market (Ettema et al., 2017). This has led to a rapidly evolving trend in use of sexed Holstein semen, conventional Holstein semen, and conventional beef semen to inseminate Holstein females in the U.S. Thus far in 2020, 20% of Holstein females are inseminated using sexed semen, whereas 23% of inseminations are beef semen on Holstein females.

From an economic perspective, the U.S. dairy industry has experienced a prolonged 5-year period of milk prices at or below the cost of production (USDA-NASS, 2020). Thus, for U.S. dairy farms to survive under this new economic environment, strategies to optimize reproductive management technologies must be evaluated, economically modeled, and transferred to the dairy industry.

Technical feasibility of the research

During the last 40 years, the NC-1201 have contributed greatly to the development of several breeding programs to maximize pregnancy rates. Moreover, efforts from this group addressed objections or reasons given by cattle producers for not adopting reproductive technologies. Information generated by this group led to the development of the OvSynch protocol in dairy cattle and its variations (CO-Synch protocols) used in beef cattle. These protocols increase pregnancy rates in both beef and dairy females compared to control treatments because they induce ovulation in postpartum cows that have not resumed estrous cycles by the end of the voluntary wait period (dairy cows) or at the onset of the breeding season (beef cows). Additionally, previous and ongoing multi-state collaborations from this group have contributed to the development of recommendations for management practices beyond ART that optimize the return of investment associated with the incorporation of these technologies.


The advantages of doing the work as a multistate effort

A foundational goal of this group is to generate statistically valid results that are applicable and relevant to dairy and beef farms across the U.S. The majority of the data endpoints, or pregnancy rates, collected in cattle breeding trials are binomial and require large sample sizes to test hypotheses and to be relevant to producers across the U. S. Hundreds, if not thousands, of cows across a variety of environmental conditions from Michigan and South Dakota to Texas and Mississippi are required to be confident that recommendations will work effectively for producers in all the varied environments across the U.S. and world, depending on specific questions. This group has collaborated on numerous multistate projects to provide results with increased statistical power for multiple farms. For example, several publications from this group were the product of the collaboration of at least six experiment stations. This group also actively collaborates, in a similar fashion, in the development of extension/outreach strategies to enhance both beef and dairy industry adoption of breeding programs.

Likely impacts from completing the work

Previous work from NC-1201 have already resulted in significant impacts to both beef and dairy industries, as the efforts of this group contributed to the current increase in the use of reproductive technologies in cattle. While significant progress has been made, expanding the use of currently available reproductive technologies and the development of novel reproductive management approaches will contribute to increasing beef and dairy production efficiency. Fertility is a main driver of the adoption of ART because the return of investment of such technologies increases as conception rates increase. The research and outreach of this proposal objectively addresses this issue and further detail is provided in the Methods and Outreach Plan sections of this proposal.



Related, Current and Previous Work

Related, current, and previous work

This group has initially focused on the developing estrus synchronization protocols that include gonadotropin release hormone, a naturally occurring hormone to control ovulation and the induction of a new growing cohort of follicles. This process is a key component to all fixed-time artificial insemination (TAI) protocols in dairy and beef cattle. This committee has subsequently built on this key process and has developed several of the TAI protocols recommended in the U.S. and throughout the world for dairy and beef cows. Major transformative industry outcomes are tied to results from this project, including the development of the Ovsynch protocol (the first successful TAI protocol for dairy cattle) and fertility programs utilizing Ovsynch for TAI in dairy cattle. These programs increase the chances of pregnancy before 130 days in milk by 20% and reduce costs of production. Ovsynch and variations (e.g. the CO-Synch protocol) used in beef cattle, and more recent modifications to such programs, increase pregnancy rates by greater than 20% and reproductive efficiency of beef cattle while decreasing labor inputs.

In both dairy and beef cattle, such protocols to induce ovulation followed by a normal reproductive cycle in cows during postpartum anestrous and prepubertal heifers. This has increased the opportunity for cows to become pregnant even if they have not resumed reproductive activity by the end of a common voluntary waiting period of 75 days in milk (dairy cows) or at the onset of the breeding season (beef cows). This increases the efficiency in beef and milk production because it reduces the chances of profitable cows being culled and reduces the interval between calving.

A signature study, “Pregnancy rates per artificial insemination for cows and heifers inseminated at a synchronized ovulation or synchronized estrus,” published in the Journal of Dairy Science by six members of this project, has been cited 745 times (Google Scholar). This has led the way to understanding the impact of Ovsynch on reproductive efficiency of dairy cattle versus the traditional method (detection of estrus). It also helped convince the dairy industry that Ovsynch can effectively manage time to first AI and reduce the number of days when cows are not in peak milk production. The impacts have revolutionized the way dairy farmers worldwide manage dairy cattle reproduction. Over 70% of dairy farms now utilize TAI protocols that utilize Ovsynch.

Through joint publications, consistent with intended outcomes of the multistate research program, this project has repeatably demonstrated the ability to coordinate multi-location experiments to improve reproductive efficiency in dairy and beef cattle.

Over the past 5 years, efforts of NC1201 scientists have resulted in: 

  • 243 multi-institution peer-reviewed articles and 323 peer-reviewed abstracts

  • $6.03 million in multi-institutional grant funding (federal and industry)

  • 184 Extension publications and popular press articles

Specific to last 5 years, efforts from this project (SD, TX, VA) has led to development of nutritional strategies to maximize fertility in beef females exposed to TAI (Brandao et al., 2018; Kruse et al., 2017) and embryo transfer (Fontes et al., 2019). A multi-state project evaluated the impacts of polyunsaturated fatty acids supplementation on embryo/conceptus development and pregnancy rates to TAI. This study showed that polyunsaturated fatty acids supplement with greater concentrations of omega-6 fatty acids increases conceptus development and consequently increased pregnancy rates to TAI by approximately 20% in beef cows (Brandão et al., 2018). Feeding companies are now manufacturing omega-6 enriched supplements specific for use in beef cow-calf herds that are now available for producers across the U.S. to take advantage of such strategies. Another multi-state effort from this group evaluated the impact of short-term after TAI nutrient restriction on embryo development (Kruse et al., 2017). This short-term nutrient restriction is commonly observed in replacement heifers that transition from a feedlot to a grazing setting after TAI. Results from this study showed a decrease in embryo development that explained decreases in fertility associated with this management practice (Kruse et al., 2017). Cattlemen are now incorporating supplementation strategies to mitigate these negative effects associated with the transition from a feedlot to a grazing setting and optimizing fertility of their herds as a consequence of the work from this group.

Additional examples of recent multi-state efforts (GA, MO, ND, SD, TX, VA, WI) from this group that are being successfully incorporated by stakeholders is the developed presynchronization approaches that increase fertility of replacement heifers exposed to TAI with (Oosthuizen et al., 2020; Mercadante et al., 2021), and increase pregnancy rates in cows in TAI (Andersen et al., 2021) and embryo transfer programs (Bonacker et al., 2020). Such efforts also led to the development of estrus synchronization protocols specific for the use of sexed semen that are now available for cattle producers and will likely increase the use of sexed semen in the beef industry (Oosthuizen et al., 2020). Moreover, resynchronization strategies have been investigated by this group in both beef (Epperson et al., 2020) and dairy cows (Barletta et al., 2017). Through the use of resynchronization programs, beef and dairy producers can expose females that failed to become pregnant in the first TAI to a second round of TAI and consequently increase the proportion of artificial insemination pregnancies.

This project has also innovated in Extension and outreach over the last 5 years. Through the Dairy Cattle Reproductive Council (DCRC) and the Beef Reproduction Task Force (BRTF; more information available at the Outreach Plan), this project has expended its impact through online delivery of Extension programming and translation of the relevant research efforts of this project. As a concrete example, the BRTF website created in 2020 had over 22,000 website visits and the BRTF protocol recommendation sheets have been downloaded over 6,800 times. The BRTF YouTube channel has over 10,000 views and the Applied Reproductive Strategies for Beef Cattle conference had more than 2,000 participants in 2020 from 31 different countries (80% from the U.S.).


  1. Increase the efficiency and predictability of sustainable reproductive technologies and management programs for beef cattle.
  2. Evaluate mechanisms that regulate reproductive processes impacting production efficiency in cattle.
  3. Disseminate reproductive management information to stakeholders to improve sustainability of cattle enterprises.


Objective 1

Increase the efficiency and predictability of sustainable reproductive technologies and management programs for beef cattle (VA, GA, MO, MS, TX, NE)

Use of pre-synchronization strategies to optimize fertility in fixed-time artificial insemination (TAI) protocols

Increased adoption of assisted reproductive technologies (ART) in the beef industry relies upon the continued development of new or modification of existing protocols to increase conception rates to TAI. The use of pre-synchronization to optimize fertility in industry-standard estrus synchronization protocols has recently been evaluated in multiple experiments. In beef females, pre-synchronization with a progesterone insert in combination with an injection of prostaglandin F 7 days before the beginning of a 7-day CO-Synch + CIDR protocol increased response to the first GnRH (Bonacker et al., 2020a; Mercadante et al., 2021), resulting in increased estrus expression and pregnancy rates to TAI (Oosthuizen et al., 2020; Mercadante et al., 2021; Andersen et al., 2021) and embryo transfer (Bonacker et al., 2020). As we continue to gain an understanding of the ovarian and endocrine response of pre-synchronized beef females, there is certainly more need to understand how these programs impact fertility in different production environments. Collaborative multi-state efforts to add pre-synchronization to improve total pregnancies per AI will continue, including exploring the effects of pre-synchronization on the fertility of Bos indicus-influenced females that have poor response to the initial GnRH (Fernandes et al., 2001).

Evaluating estrus synchronization protocols specific to the use of sexed semen

Timing of insemination relative to ovulation has been reported to affect fertilization rate and embryo quality. When sex-sorted semen is used, the optimal timing of AI is thought to be later (i.e., closer to ovulation) than when conventional semen is used. However, because of the variability among females in timing of insemination relative to ovulation when TAI is performed, it remains unclear whether optimal timing of TAI differs based on semen types. Some studies in which TAI have been performed at later times suggest no difference (Hall et al., 2017; Ketchum et al., 2021). However, improvements associated with later timing of TAI may be realized in a synchronization protocol-specific manner and may be more likely to be observed in protocols in which pre-synchronization treatments result in more synchronous and/or altered timing of estrus onset (Oosthuizen et al., 2021). Research efforts within our groups will continue to evaluate optimal timing of insemination with sexed semen in a protocol-specific manner and in conjunction with efforts to incorporate pre-synchronization treatments.

Combining color Doppler ultrasound with resynchronization to decrease the interval between artificial inseminations in beef herds

Resynchronization programs have been developed to maximize the proportion of pregnancies generated via reproductive technologies (Epperson et al., 2020). However, the long interval between breeding events (approximately 30 to 40 days) of currently recommended resynchronization protocols limits their adoption, as beef cattle producers focus on generating pregnancies early in the breeding season. The main factor increasing the interval between breeding events is the period between the first breeding and pregnancy diagnosis, which is performed via conventional transrectal ultrasonography and limited to days 28-30 of gestation (Nation et al., 2003). Recent research from this group indicates that the use of color Doppler ultrasound examination of the corpus luteum can successfully diagnose pregnancy on day 20 of gestation in Bos taurus beef females (Holton et al., 2021). Based on these results we propose to evaluate the use of color Doppler in combination with early resynchronization protocols to increase the proportion of genetically superior pregnancies while minimizing the interval between the first and second insemination.


Objective 2

Evaluate mechanisms that regulate reproductive processes impacting production efficiency in cattle


Beef Cattle (MS, NM, TN, TX, US MARC, NE, VA, WY)


Evaluating the mechanisms associated with early pregnancy establishment

Conception early in the breeding season and maintenance of that pregnancy to calving requires many mechanisms to be in synchrony and in communication at the correct time. Thus, early embryonic losses have been estimated to be as large as 60% (between fertilization and day 60 of pregnancy). This is important to overall profitability since heifers that calved during the first 21 days of the calving season had increased longevity in the cow herd compared to heifers that calved later (Cushman et al., 2013). Not all stressors during early pregnancy result in early embryonic mortality, some result in changes in the developmental programming of the progeny. Therefore, a need exists to understand mechanisms that regulate the uterine environment, early embryonic development, and maintenance of pregnancy. Research will focus on identifying mechanisms that are essential for establishing a pregnancy and the impact of changes that occur during early pregnancy on future productivity of the offspring. Factors investigated will include preovulatory steroid production, estrus expression, nutritional impacts, male related factors influencing early embryo development, and the influence of the ovarian reserve on oocyte quality and uterine function.

Investigating male-related factors influencing pregnancy rates in beef herds

As the use of estrus synchronization and TAI increased, it became apparent that certain bulls had poorer conception rates in a TAI setting compared to when they were used in either a natural service or heat detection scenario. Components of the ejaculate must work in conjunction with the maternal system to create a uterine environment that facilitates the successful establishment and maintenance of pregnancy (Mullen et al., 2012). However, the exact role of ejaculate components as mediators of inflammation mediators (Bromfield et al., 2014; Ibrahim et al., 2019), and how these substrates influence the uterine environment during the establishment of pregnancy are not well understood. These observations also stimulated inquiry into what contributes to sperm longevity and sperm transport. The plasma membrane of spermatozoa is coated with a plethora of glycoproteins (Magargee et al., 1988) while the epididymis contains several enzymatic proteins that are thought to be involved in spermatozoa protection (Girouard et al., 2011) or motility (Frenette et al., 2004).  Additionally, research has provided evidence that sperm is an important contributor to early embryonic development and consequently pregnancy establishment (Yuan et al., 2015). Research will focus on understanding male related factors that impact sperm function, fertility, and early embryo development.

Investigating epigenetic mechanisms associated with developmental programming of cattle performance

Previous results demonstrated that early embryonic development in vitro is improved in oocytes harvested from heifers and cows with increased numbers of follicles (Tessaro et al., 2011; Cushman and Perry unpublished data). These results indicate that epigenetic mechanisms controlling early embryonic development are improved in these oocytes. Thus, a need exists for understanding and validating the epigenetic mechanisms controlling developmental programming. A number of studies have demonstrated impacts of fetal programming on progeny performance. Research will focus on identifying consistent changes in epigenetic mechanisms across locations (e.g., environments and production systems). Based on the results from these analyses, we will initiate a multi-state experiment that attempts to developmentally program progeny consistently across locations. Nutritional programming of heifers also continues past the in-utero development stage and during the first year of life. Heifers managed on a stair-step growth pattern, with reduced caloric intake during the peri-pubertal period, have increased numbers of primordial follicles in their ovaries at initiation of their first breeding season (Freetly et al., 2014; Amundson et al., 2015; Rosasco et al., 2020). These results suggest mechanisms controlling primordial follicle activation may be slowed due to utilization of a stair-step compensatory growth program, however these mechanisms are not well understood. Research will focus on identifying mechanisms contributing to the influence of nutritional programming on the ovarian reserve and reproductive efficiency.


Dairy Cattle (CA, IL, KS, MI, VA, WI)

Evaluating the impact of timing of insemination with sexed semen in dairy fertility programs

The rate at which heifers become pregnant is determined by an interaction between AI service rate and conception rate (P/AI). Service rate can be increased by using synchronized breeding programs tailored specifically for dairy heifers. In contrast to lactating cows, dairy heifers respond poorly to synchronization protocols based solely on GnRH and PGF2a such as Ovsynch (Pursley et al., 1997). This is due to differences in circulating progesterone concentrations (Sartori et al., 2004) and an increased rate of follicular wave turnover in heifers (Bisinotto and Santos, 2011) which decreases protocol synchrony (Lima et al., 2013). Inclusion of a controlled intravaginal progesterone insert (EAZI-Breed CIDR, Zoetis, Madison, NJ) during the protocol prevents heifers from displaying estrus until CIDR insert removal thereby increasing protocol synchrony (Rivera et al., 2005). The TAI protocol recommended for use in dairy heifers by the Dairy Cattle Reproduction Council is the 5-d CIDR-Synch protocol (Lima et al., 2013). The 5-d CIDR-Synch protocol for TAI yields conception rates between 50% to 60% when using conventional semen (Lima et al., 2013) and increases the AI service rate thereby decreasing days to first AI and days to pregnancy compared with heifers receiving AI to a detected estrus (Silva et al., 2015). The decreased days to first insemination and pregnancy using the 5-d CIDR-Synch protocol in turn decreases days on feed (Silva et al., 2015) which is the greatest cost associated with raising dairy replacements. A caveat with the 5-d CIDR-Synch protocol is that 27% to 33% of heifers display estrus >24 h before scheduled TAI (Masello et al., 2019; Silva et al., 2015). This makes detection of estrus during the 5-d CIDR-Synch protocol a requirement to achieve acceptable conception rates.

One of the first experiments to evaluate use of sexed semen in lactating cows used an activity monitoring system in Jersey cows to TAI based on increased activity (Bombardelli et al., 2016). Overall, pregnancy rates using sexed semen was greatest for Jersey cows inseminated between 23 and 41 h after the onset of activity (Bombardelli et al., 2016) which is later than the optimal timing for conventional semen of 8 to 16 h after the onset of activity using an activity monitoring system (Stevenson et al., 2014). Thus, an idea in the dairy industry today is that timing of AI using sexed semen should occur closer to the time of ovulation than conventional semen. From a physiologic perspective, this may be due to the sexing process inducing a capacitation-like state of sperm (Maxwell et al., 1996). We have reported a positive relationship between the interval from onset of activity associated with behavioral estrus using an activity monitoring system and milk production near the time of estrus (Valenza et al., 2012). Thus, inseminating high-producing cows later using sexed semen may be optimal for cows inseminated to estrus because ovulation occurs later relative to the onset of estrus in high-producing cows as milk production near the time of estrus increases. A critical knowledge gap is that the optimal timing of AI using sexed semen has not been established when the interval from timing of AI to ovulation is controlled using a fertility program at first service. We propose to characterize optimal timing of AI using sexed semen and its cost benefits for fertility program in dairy cows and heifers. This is intricate investigation to undertake, requiring large numbers of dairy cows and dairy heifers (a strength of this multi-state project). One valid reason for inconsistency of results in studies evaluating the impact of timing of insemination with sexed semen is the differences in environment and reproductive programs used. This is an issue that this multi-state projected is capable to address, having a long history of working across locations to compile data using a common experimental design. Furthermore, this area is a need in beef systems as well, and the unique combination of both dairy and beef interests in this group will enhance developments in this area.

Investigating the impacts associated with improved reproductive performance in females with greater genomic prediction for daughter pregnancy rate (GDPR)

In a recent study from our group, it was reported genomic prediction to daughter pregnancy rate (GDPR), in primiparous and multiparous cows, was positively associated with pregnancy for the first service, number of days to the first service, pregnancy at 300 days in milk, time from calving to pregnancy, and number of services for conception, a group of reproductive parameters that is not necessarily dependent on estrus detection in herds receiving timed AI (Lima et al., 2020). In fact, breeding code (i.e., estrus detection or TAI) was not a significant predictor for first service reproductive performance. In another study using Holstein heifers exclusively, high GDPR was associated with larger ovulatory follicles and a tendency to ovulate more when evaluated at 96 h after the onset of estrus than herd mates with low GDPR (Veronese et al., 2019). Previously, genetic merit for fertility traits in lactating dairy cows was also positively associated with larger ovulatory follicles, greater plasma progesterone concentrations from d 6 to 13 post-ovulation, and a tendency of increased estradiol at proestrus compared with cows with low genetic merit (Cummins et al., 2012). Other related findings include a greater concentration of pregnancy-specific protein B from d 28 to 35 post-AI in heifers with high GDPR compared with heifers with low GDPR (Veronese et al., 2019). It is a novel finding that pregnancy-specific protein B, which is produced by the conceptus, is associated with the GDPR of the heifer (maternal component). These results indicate that high GDPR, and hence improved fertility, might be mediated by an enhanced dominant follicle and increased plasma levels of estradiol that translate into improved embryo and conceptus development post insemination. However, the mechanisms by which GDPR lead to improved reproductive response in high-producing dairy cows bred after timed AI remain unclear and further research is needed to determine if high GDPR is linked to follicle development and ovulatory responses of cows and heifers subjected to timed AI programs. We propose to characterize estrous cycle synchronization responses and hormonal profile in genotyped Holstein dairy cows and heifers to further understand the mechanisms associated with greater fertility in females with high GDPR.

Evaluating the luteotropic mechanisms associated with the use of nerve growth factor- β (NGF)

Another key factor contributing pregnancy maintenance in dairy cows is concentrations of progesterone (P4) post-AI. Although studies have shown the benefits of using supplemental P4 early in the luteal phase to improve pregnancy per AI, the timing of administration appears to be crucial for enhancing embryonic development (O’hara et al., 2014). Initiating P4 supplementation on day 4 post-estrus resulted in significantly greater embryo length than control heifers with experimentally induced sub luteal function, whereas P4 supplementation beginning on day 7 did not have a "rescue" effect (Parr et al., 2017). While short-term P4 supplementation from days 3 to 7 after estrus increased conceptus size and interferon-τ production in heifers, it also led to a paradoxical increased number of short cycles (O’hara et al., 2014). Therefore, strategies aimed at improving the development of the endogenous P4 produced by the CL or administration of luteotropic agents have been proposed to prevent these potential negative effects. A commonly described mechanism for increasing peripheral P4 concentrations is administering human chorionic gonadotropin (hCG) (Rizos et al., 2012). This LH-like hormone induces ovulation of the first wave dominant follicle to form accessory CL that will produce additional P4. While administration of hCG from 5 to 7 days after AI increases P4 concentrations in dairy cows, the effects on pregnancy rates have been inconsistent (Stevenson et al., 2007). Like exogenous P4 supplementation, the timing of hCG administration seems to be a contributing factor to its variable success. The potential variability among individual and animal categories in metabolism of plasma P4 likely contributes to the inconsistent results of current strategies to improve progesterone in cattle. Data from our group indicates that intramuscular treatment with nerve growth factor-β (NGF), a seminal plasma protein abundant in bovine seminal plasma, at time of the final GnRH of the synchronization protocol in dairy heifers and in beef and dairy cows (Stewart et al., 2020; Hubner et al., 2021) augmented P4 in a manner that resembles the physiological increase reported in cattle. The consistent results of NGF treatments provide a novel technology and pathway to improve plasma P4 that need to be critically evaluated as a tool to improve reproductive efficiency in cattle. We will determine the mechanisms by which NGF elicits its luteotropic effects in the hypothalamic-pituitary-ovarian axis and if the responses to NGF can be harnessed therapeutically to improve reproductive efficiency of dairy cows.

 Objective 3

Disseminate reproductive management information to stakeholders to improve sustainability of cattle enterprises (GA, MI, TX, WI, NE, MS, MI, VA)

 A description of objective 3 is available in the Outreach Plan section of this proposal.

Measurement of Progress and Results


  • All research proposed herein will be completed during the 5-year proposal period. Results of research will be published in experiment station reports, refereed publications, and in popular press articles. Research results will also be delivered to stakeholders in Extension meetings described in the outreach portion of this proposal. In addition, decision aid tools will be developed to assist cattle producers to enhance their ability to incorporate new reproductive management practices into their operations.

Outcomes or Projected Impacts

  • The main outcome of the experiments proposed herein is to enhance animal production and animal products in the U.S. through the development and dissemination of assisted reproductive technologies (ART). Therefore, the proposed effort fits current priority areas identified by the USDA. In beef cattle, suboptimal fertility results in cows failing to become pregnant or becoming pregnant later in the end of the breeding season. The estimated cost of pregnancy failure in beef herds is approximately 1 billion dollars annually in the U.S. In addition to the costs associated with pregnancy failure, 1.1 kg of weaning weight is lost per calf for each day in which conception is delayed. This occurs because cows that become pregnant later in the breeding season, and consequently calve later in the calving season, produce younger and lighter calves at weaning. Work from this group has shown that estrus synchronization and TAI increase the proportion of cows becoming pregnant in the beginning of the breeding season and consequently increase weaning weights by 17 kg per cow exposed to the breeding season. It is estimated that 2 to 3 million beef females are exposed to these synchronization programs today. Increasing the performance of ART and expanding their use through the research and outreach efforts of this proposal could result in 459 million additional kilograms of weight in calves ($1.52 billion) at weaning and substantially impact the profitability of cow-calf producers. Additionally, this would be accomplished while disseminating superior genetics across the industry which would indirectly improve profitability in other segments of the beef industry, such as feedlots and retailers. Recent studies reveal that cows are being sold or culled from herds at alarming rates due to reproductive inefficiencies, an issue costing the U.S. dairy and beef industries over $1 billion each year. Dairy farmers whose cows do not conceive before 130 days in milk – which happens 50 percent of the time – annually lose about $380 per cow. Additionally, from an economic perspective, the US dairy industry has experienced a prolonged 5-year period of milk prices at or below the cost of production (USDA-NASS, 2020). Thus, for U.S. dairy farms to survive under this new economic environment, strategies to optimize reproductive management technologies must be evaluated, economically modeled, and transferred to the dairy industry. The research and outreach proposed herein have the potential to address these challenges in a timely manner and increase dairy production efficiency in the U. S. through optimized fertility programs.


(2022):Initiate the proposed experiments associate with the refinement of reproductive programs, and the discovery of nutritional, physiological, and molecular factors that impact beef and dairy cattle fertility.

(2023):Generate preliminary reports describing the factors associated with fertility in cattle and generate multi-state data for optimization of reproductive programs.

(2024):Initiate summaries of updated recommendations based on the findings obtained during the first two years.

(2025):Disseminate information to the scientific community, cattle producers, veterinarians, and industry professionals.

(2026):Publish findings in peer-reviewed scientific journals.

Projected Participation

View Appendix E: Participation

Outreach Plan

Beyond traditional refereed and extension publications, the NC1201 committee members have led the development of two specific outreach organizations to enhance reproductive efficiency nationwide. These organizations work closely with university extension and research communities, the pharmaceutical industry, the AI industry and the veterinary community to enhance reproductive efficiency of U.S. dairy and beef cattle operations.

The Dairy Cattle Reproduction Council (DCRC) ( works to raise awareness and long-term interest in issues critical to reproductive performance in dairy cattle and delivers the latest in technology and resources to the industry.

The Beef Reproduction Task Force ( /) works to identify the most reliable beef cattle reproduction management strategies and develop methods for delivery of beef cattle reproduction management strategies into Extension programs.

These organizations provide unique means for multi-state dissemination of science-based information. This includes annual conferences, webinars, and experiential learning programs for beef and dairy producers. Several of which are made available to anyone through YouTube videos and publications free of charge. Additionally, this material is also used by Extension personnel that are not necessarily associated with this group, contributing to their local dissemination of information on reproduction to stakeholders.

The development of fertility programs through this project have collectively contributed to increased use of timed AI. Impacts include:

Increased adoption of profitable timed AI in both U.S. dairy and beef herds

  • Conservative estimated savings of $80 per cow per year, or $7.2 billion industrywide, since publication of the initial collaborative study in 1997

  • Fertility programs in beef and dairy cows developed by this group is now the basis for many programs utilized in every part of the world

  • Fertility programs give dairy farmers the confidence to use more gender-selected semen to generate more females from top genomic-ranked cows and enhance genetic progress. This in turn is allowing more beef semen to be utilized on the lower genomic-ranked cows to improve profitability of bull calves going to market.

  • Use of beef semen on dairy cows and fertility programs for beef herds resulted in record high semen sales – approximately 4-fold increase from 10 years ago.

  • For every beef cow exposed to a TAI protocol, a producer will gain $49 per cow after weaning.

  • Today, approximately 2 million cows annually undergo TAI in the U.S. with an estimated economic impact of $98 million for the beef industry.

The proposed project will continue to manage these previously established outreach programs and use this outreach structure to share the novel ongoing developments in reproductive management and reproductive efficiency proposed by this group, engaging stakeholders and disseminating recommendations that increase productivity and profitability of beef and dairy herds.


The technical committee will consist of at least 1 officially designated representative from each participating agricultural station in the region. The technical committee will meet annually. The USDA-NIFA designate one nonvoting representative. Officers will be elected for a rotating period of 3 years, consisting of Chair, Secretary and a Member-at-Large. Officers rotate from Member-at-Large to Secretary to Chair during each subsequent year. Elections will be held at the annual meeting. Officers will compose the executive committee. The executive committee, together with the administrative advisors, is authorized to function on behalf of the technical committee in all matters pertaining to the regional project interim action.

The chair, in consultation with the administrative adviser, will arrange the time and place of the meeting, notify technical committee members of the meeting site, and prepare the agenda. The Chair 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 Chair as needed for specific assignments. The executive committee will be in charge of coordinating the cooperative research trials.

Literature Cited

Literature Cited

Amundson, O. L., T. H. Fountain, E. L. Larimore, B. N. Richardson, A. K. McNeel, E. C. Wright, D. H. Keisler, R. A. Cushman, G. A. Perry, H. C. Freetly. 2015. Postweaning nutritional programming of ovarian development in beef heifers. J. Anim. Sci. 93:5232–5239. doi:10.2527/jas.2015-9067.

Andersen, C.M., R.C. Bonacker, E.G. Smith, C.M. Spinka, S.E. Poock, and J.M. Thomas. 2021. Evaluation of the 7 & 7 Synch and 7-day CO-Synch + CIDR treatment regimens for control of the estrous cycle among beef cows prior to fixed-time artificial insemination with conventional or sex-sorted semen. Anim. Reprod. Sci. 235:106892. doi:10.1016/j.anireprosci.2021.106892.

Barletta, R.V., P.D. Carvalho, V.G. Santos, L.F. Melo, C.E. Consentini, A.S. Netto, and P.M. Fricke. 2017. Effect of dose and timing of prostaglandin F2α treatments during a Resynch protocol on luteal regression and fertility to timed artificial insemination in lactating Holstein cows. J. Dairy Sci. 101:1730-1736. doi:10.3168/jds.2017-13628.

Bisinotto, R. S., and Santos, J. E. P. 2011. The use of endocrine treatments to improve pregnancy rates in cattle. Reprod. Fertil. Dev. 24:258-266. doi:10.1071/RD11916.

Bombardelli, G.D., H.F. Soares, and R.C. Chebel. 2016. Time of insemination relative to reaching activity threshold is associated with pregnancy risk when using sex-sorted semen for lactating Jersey cows. Theriogenology. 85:533-539. doi:10.1016/j.theriogenology.2015.09.042.

Bonacker, R.C., K.R. Gray, C.A. Breiner, J.M. Anderson, D.J. Patterson, C.M. Spinka, J.M. Thomas. 2020. Comparison of the 7 & 7 Synch protocol and the 7-day CO-Synch + CIDR protocol among recipient beef cows in an embryo transfer program. Theriogenology. 158:490-496. doi: 10.1016/j.theriogenology.2020.09.033.

Bonacker, R.C., K.S. Stoecklein, J.W.C. Locke, J.N. Ketchum, E.R. Knickmeyer, C.M. Spinka, S.E. Poock, and J.M. Thomas. 2020. Treatment with prostaglandin F2α and an intravaginal progesterone insert promotes follicular maturity in advance of gonadotropin-releasing hormone among postpartum beef cows. Theriogenology. 157:350-359. doi:10.1016/j.theriogenology.2020.08.018.

Bromfield, J.J. 2014. Seminal fluid and reproduction: much more than previously thought. J. Assist. Reprod. Genet. 31:627–636. doi:10.1007/s10815-014-0243-y.

Brandão, A. P., R. F. Cooke, K. M. Schubach, R. S. Marques, D. W. Bohnert, R. S. Carvalho, N. W. Dias, C. L. Timlin, S. Clark-Deener, J. F. Currin, D. B. Jump, K. G. Pohler, R. L. A. Cerri, and V. R. G. Mercadante. 2018. Supplementing Ca salts of soybean oil after artificial insemination increases pregnancy success in Bos taurus beef cows. J. Anim. Sci. 96:2838–2850. doi:10.1093/jas/sky156.

Caraviello, D.Z., K.A. Weigel, P.M. Fricke, M.C. Wiltbank, M.J. Florent, N.B. Cook, K.V. Nordlund, N.R. Zwald, and C.L. Rawson. 2006. Survey of management practices on reproductive performance of dairy cattle on large US commercial farms. J. Dairy Sci. 89:4723–4735. doi: 10.3168/jds.S0022-0302(06)72522-X.

Carvalho, P.D., V.G. Santos, J.O. Giordano, M.C. Wiltbank, and P.M. Fricke. Development of fertility programs to achieve high 21-day pregnancy rates in high-producing dairy cows. Theriogenology. 114:165-172. doi:10.1016/j.theriogenology.2018.03.037.

Cushman, R. A., L. K. Kill, R. N. Funston, E. M. Mousel, and G. A. Perry. 2013. Heifer calving date positively influences calf weaning weights through six parturitions. J. Anim. Sci. 91:4486–4491. doi: 10.2527/jas.2013-6465.

Epperson, K.M., J.J. Rich, S.M. Zoca, E.J. Northrop, S.D. Perkins, J.A. Walker, J.R. Rhoades, and G.A. Perry. 2020. Effect of progesterone supplementation in a resynchronization protocol on follicular dynamics and pregnancy success. Theriogenology.157:121-129. doi:10.1016/j.theriogenology.2020.07.011.

Ettema, J.F., J.R. Thomasen, L. Hjortø, M. Kargo, S. Østergaard, and A.C. Sørensen. 2017. Economic opportunities for using sexed semen and semen of beef bulls in dairy herds. J. Dairy Sci. 100:4161-4171. doi:10.3168/jds.2016-11333.

FAO. 2009. How to feed the world in 2050. Insights from an expert meet. FAO. 2050: 1-35. doi: 10.1111/j.1728-4457.2009.00312.x.

Fernandes, P., A.B. Teixeira, A.J. Crocci, and C.M. Barros. 2001. Timed artificial insemination in beef cattle using Gn RH agonist, PGF2alpha and estradiol benzoate (EB). Theriogenology. 55:1521-1532. doi:10.1016/S0093-691X(01)00499-X.

Fontes P. L. P., N. Oosthuizen, F. M. Ciriaco, C. D. Sanford, L.B. Canal, K. G. Pohler, D. D. Henry, V. R. G. Mercadante, C. L. Timlin, A. D. Ealy, S. E. Johnson, N. DiLorenzo, and G. C. Lamb. 2019. Impact of fetal versus maternal contributions of Bos indicus and Bos taurus genetics on embryonic and fetal development. J. Anim. Sci. 97:1645-165. doi: 10.1093/jas/skz044.

Frenette, G., C. Lessard, and R. Sullivan. 2004. Polyol pathway along the bovine epididymis. Mol. Reprod. Dev., 69: 448-456. doi:10.1002/mrd.20170.

Freetly, H. C., K. A. Vonnahme, A. K. McNeel, L. E. Camacho, O. L. Amundson, E. D. Forbes, C. A. Lents, and R. A. Cushman. 2014. The consequence of level of nutrition on heifer ovarian and mammary development. J. Anim. Sci. 92:5437-5443. doi:10.2527/jas.2014-8086.

Girouard, J., G. Frenette, and R. Sullivan. 2011. Comparative proteome and lipid profiles of bovine epididymosomes collected in the intraluminal compartment of the caput and cauda epididymidis. Int. J. Androl. 34:e475-e486. doi:10.1111/j.1365-2605.2011.01203.x

Hall, J.B., R.K. Kasimanickam, J.B. Glaze, and M.C. Roberts-Lew. 2017. Impact of delayed insemination on pregnancy rates to gender selected semen in a fixed-time AI system. Theriogenology.102:154-161. doi:10.1016/j.theriogenology.2017.07.014.

Hubner, A.M., I.F. Canisso, P.M. Peixoto, A.J. Conley, F.S. Lima. 2021. Effect of GnRH administered at the time of artificial insemination for cows detected in estrus by conventional estrus detection or an automated activity-monitoring system. J. Dairy Sci. doi:10.3168/jds.2021-21011.

Holton, M. P., N. Oosthuizen, G. D. de Melo, D.B. Davis, R. L. Stewart, Jr., K. G. Pohler, G.C. Lamb and P. L. P. Fontes. 2021. Color Doppler ultrasonography for early pregnancy diagnosis in postpartum Bos taurus beef cows. J. Anim. Sci. (Abstract - In press).

Ibrahim, L.A., J.A. Rizo, P.L.P. Fontes, G.C. Lamb, J.J. Bromfield. 2018. Seminal plasma modulates expression of endometrial inflammatory mediators in the bovine. Biol. Reprod. 100: 660-671. doi:10.1093/biolre/ioy226.

Ketchum, J.N., R.C. Bonacker, C.M. Andersen, E.G. Smith, K.S. Stoecklein, C.M. Spinka, J.M. Thomas. 2021. Evaluation of later timepoints for split-time artificial insemination when using sex-sorted semen among beef heifers following the 14-d CIDR®-PG protocol. Anim. Reprod. Sci. 224:106649. doi:10.1016/j.anireprosci.2020.106649.

Khalajzadeh, S., A. Nejati-Javaremi, and H. Mehrbani Yeganeh. 2012. Effect of widespread and limited use of sexed semen on genetic progress and reproductive performance of dairy cows. Animal. 6:1398-1406. doi:10.1017/S1751731112000651.

Kruse, S.G., G.A. Bridges, B.J. Funnell, S.L. Bird, S.L. Lake, R.P. Arias, O.L. Amundson, E.L. Larimore, D.H. Keisler, and G.A. Perry. Influence of post-insemination nutrition on embryonic development in beef heifers. Theriogenology. 90:185-190. doi:10.1016/j.theriogenology.2016.11.021.

Lamb, G. C., V. R. G. Mercadante, D. D. Henry, P. L. P. Fontes, C. R. Dahlen, J. E. Larson, and N. DiLorenzo. 2016. Invited Review: Advantages of current and future reproductive technologies for beef cattle production. Prof. Anim. Sci. 32:162–171.

Lima, F.S., F.T. Silvestre, F. Peñagaricano, and W.W. Thatcher. Early genomic prediction of daughter pregnancy rate is associated with improved reproductive performance in Holstein dairy cows. J. Dairy Sci. 103:3312-3324. doi: 10.3168/jds.2019-17488.

Lima F.S., E.S. Ribeiro, R.S. Bisinotto, L.F. Greco, N. Martinez, M. Amstalden, W.W. Thatcher, and J.E.P. Santos. 2013. Hormonal manipulations in the 5-day timed artificial insemination protocol to optimize estrous cycle synchrony and fertility in dairy heifers. J. Dairy Sci. 96:7054-7065. doi: 10.3168/jds.2013-7093.

Magargee, S.F., E. Kunze, R.H. Hammerstedt. 1988. Changes in Lectin-Binding Features of Ram Sperm Surfaces Associated with Epididymal Maturation and Ejaculation. Biol. Reprod. 38:667–685. doi:10.1095/biolreprod38.3.667.

Masello, M., M.M. Perez, G.E. Granados, M.L. Stangaferro, B. Ceglowski, M.J. Thomas, and J.O. Giordano. Reproductive performance of replacement dairy heifers submitted to first service with programs that favor insemination at detected estrus, timed artificial insemination, or a combination of both. J. Dairy Sci. 102:1671-1681. doi: 10.3168/jds.2018-15200. 

Maxwell, W.M., G.R. Welsh, L.A., Johnson.1996. Viability and membrane integrity of spermatozoa after dilution and flow cytometric sorting in the presence or absence of seminal plasma. Reproduction, Fertility and Development 8, 1165-1178. doi:10.1071/RD9961165

Mensbrugghe, D. V. D., I. Osorio-Rodarte, A. Burns, and J. Baffes. 2009. Macroeconomic environment, commodity markets: a longer term outlook. Food Agric. Organ. United Nations. (Accessed 15 November 2019).

Mercadante, V. R. G., G. C. Lamb, N. Oosthuizen, N. W. Dias, S. Pancini, H. Haines, J. Currin, S. Clark, J. L. Stewart, G. J. Pent, M. P. Holton, D. D. Davis, S. R. Hernandez, R. L. Stewart, P. L. P. Fontes. 2021. Estrus Response and Pregnancy Rates of Beef Replacement Heifers Enrolled in Two Fixed-time Artificial Insemination Protocols, with or Without Pre-synchronization. J. Anim. Sci. (In press).

Mullen, M. P.; Elia, G.; Hilliard, M.; Parr, M. H.; Diskin, M. G.; Evans, A. C. O.; Crowe, M. A. Proteomic Characterization of Histotroph during the Preimplantation Phase of the Estrous Cycle in Cattle. J. Proteome Res. 2012, 11 (5), 3004– 3018,  DOI: 10.1021/pr300144q.

Nation D.P., J. Malmo, G.M. Davis, K.L. Macmillan. 2003.Accuracy of bovine pregnancy detection using transrectal ultrasonography at 28 to 35 days after insemination. Aust. Vet. J. 81:63-65. doi: 10.1111/j.1751-0813.2003.tb11435.x.

National Animal Health Monitoring System (NAHMS), 2014. Health and Management Practices on U.S. Dairy Operations. USDA-APHIS, Fort Collins, CO, USA.

Norman, H.D., J.R. Wright, S.M. Hubbard, R.H. Miller, J.L. Hutchison. 2020. Reproductive status of Holstein and Jersey cows in the United States. J. Dairy Sci. 92:3517-3528. doi:10.3168/jds.2008-1768.

O’Hara L., Forde N., Carter F., Rizos D., Maillo V., Ealy A. D., Kelly A. K., Rodriguez P., Isaka N., Evans A. C. O., Lonergan P. 2013. Paradoxical effect of supplementary progesterone between Day 3 and Day 7 on corpus luteum function and conceptus development in cattle. Reprod. Fertil. Dev. 26:328-336. doi:10.1071/RD12370/

Oosthuizen, N., P. L. P. Fontes, R. V. Oliveira Filho, C. R. Dahlen, D. M. Grieger, J. B. Hall, S. Lake, C. R. Looney, V. R. G. Mercadante, B.W. Neville, G. A. Perry, J. G. Powell, L. D. Prezotto, G. E. Seidel, R. S. Walker, R. C. Cardoso,  K. G. Pohler, and G. C. Lamb. 2020. Presynchronization and delayed fixed-time artificial insemination increases pregnancy rates with sex-sorted semen in replacement beef heifers. Anim. Reprod. Sci. 226:106699. doi:10.1016/j.anireprosci.2021.106699.

Oosthiuzen, N., P. L. P. Fontes¸ K. Porter, G. C. Lamb. 2020. Presynchronization with prostaglandin F and prolonged exposure to exogenous progesterone impact estrus expression and fertility in beef heifers. Theriogenology. 146: 88-93. doi:10.1016/j.theriogenology.2020.02.010.

Parr, M.H., S. Scully, P. Lonergan, A.C.O. Evans, M.A. Crowe, M.G. Diskin. 2017. Establishment of critical timing of progesterone supplementation on corpus luteum and embryo development in beef heifers. Anim. Reprod. Sci. 180:1-9. doi:10.1016/j.anireprosci.2017.02.005.

Pursley, J.R., M.C. Wiltbank, J.S. Stevenson, J.S. Ottobre, H.A. Garverick, L.L. Anderson. 1997. Pregnancy Rates Per Artificial Insemination for Cows and Heifers Inseminated at a Synchronized Ovulation or Synchronized Estrus. J. Dairy Sci. 80:295-300. doi:10.3168/jds.S0022-0302(97)75937-X.

Reese, S.T., G.A. Franco, P. K. Poole, R. Hood, L. Fernadez Montero, R.V. Oliveira Filho, R. F. Cooke, K. G. Pohler. 2020. Pregnancy loss in beef cattle: A meta-analysis. Anim Reprod Sci. 212:106251.

Rizos, D., S. Scully, A.K., Kelly, A.D. Ealy, R. Moros, P. Duffy, A. Al Naib, N. Forde, and P. Lonergan. 2011. Effects of human chorionic gonadotrophin administration on Day 5 after oestrus on corpus luteum characteristics, circulating progesterone and conceptus elongation in cattle. Reprod. Fertil. Dev. 24, 472-481. doi:10.1071/RD11139.

Rosasco, S.L., E.A. Melchior, S.H. Cox, R.L. Dunlap, J.A.H. Gifford, E.J. Scholljegerdes, R.A. Cushman, and A.F. Summers. 2020. Effect of stair-step nutritional programming on ovarian development in replacement beef heifers. Trans. Anim. Sci. 4:S32–S36. doi:10.1093/tas/txaa092.

Sans, P., and P. Combris. 2015. World meat consumption patterns: An overview of the last fifty years (1961–2011). Meat. Sci. 109:106–111.

Santos, V.G., P.D. Carvalho, C. Maia, B. Carneiro, A. Valenza, P.M. Fricke. 2017. Fertility of lactating Holstein cows submitted to a Double-Ovsynch protocol and timed artificial insemination versus artificial insemination after synchronization of estrus at a similar day in milk range. J. Dairy Sci. 100:8507-8517. doi:10.3168/jds.2017-13210.

Sartori, R., J.M. Haughian, R.D. Shaver, G.J.M. Rosa, M.C. Wiltbank. 2004. Comparison of Ovarian Function and Circulating Steroids in Estrous Cycles of Holstein Heifers and Lactating Cows. J. Dairy Sci. 87:905-920. doi:10.3168/jds.S0022-0302(04)73235-X.

Silva, T.V., F.S. Lima, W.W. Thatcher, J.E.P. Santos. 2015. Synchronized ovulation for first insemination improves reproductive performance and reduces cost per pregnancy in dairy heifers. J. Dairy Sci. 98:7810-7822. doi:10.3168/jds.2015-9704.

Stevenson, J.S., M.A. Portaluppi, D.E. Tenhouse, A. Lloyd, D.R. Eborn, S. Kacuba, J.M. DeJarnette. Interventions After Artificial Insemination: Conception Rates, Pregnancy Survival, and Ovarian Responses to Gonadotropin-Releasing Hormone, Human Chorionic Gonadotropin, and Progesterone. J. Dairy Sci. 90:331-340. doi:10.3168/jds.S0022-0302(07)72634-6.

Stevenson, J.S. , S.L. Hill, R.L. Nebel, and J.M. DeJarnette. 2007. Ovulation timing and conception risk after automated activity monitoring in lactating dairy cows. J. Dairy Sci. 97:4296-4308. doi:10.3168/jds.2013-7873.

Stewart, J.L., S. Stella, L.L. Cunha, N.W. Dias, I.F. Canisso, V.R.G. Mercadante, R.C. Cardoso, G.L. Williams, K.G. Pohler, F.S. Lima. 2020. Administration of nerve growth factor-β to heifers with a pre-ovulatory follicle enhanced luteal formation and function and promoted LH release. Theriogenology. 148:37-47. doi:10.1016/j.theriogenology.2020.02.040.

Tessaro, I., A. M. Luciano, F. Franciosi, V. Lodde, D. Corbani, S. C. Modina. 2011. The endothelial nitric oxide synthase/nitric oxide system is involved in the defective quality of bovine oocytes from low mid-antral follicle count ovaries. J. Anim. Sci. 89:2389–2396. doi:10.2527/jas.2010-3714.

USDA. 2020. Beef 2017, “Beef Cow-calf Management Practices in the United States, 2017, report 1.” USDA–APHIS–VS–CEAH–NAHMS. Fort Collins, CO. #.782.0520.

USDA. National Agricultural Statistical Service – Quick Stats. 2020. Accessed 2020-11-30.

Valenza, A., J.O. Giordano, G. Lopes, L. Vincenti, M.C. Amundson, and P.M. Fricke. Assessment of an accelerometer system for detection of estrus and treatment with gonadotropin-releasing hormone at the time of insemination in lactating dairy cows. J. Dairy Sci. 95:7115-7127. doi:10.3168/jds.2012-5639.

Veronese, A. O. Marques, F. Peñagaricano, R.S. Bisinotto, K.G. Pohler, T.R. Bilby, R.C. Chebel. Genomic merit for reproductive traits. II: Physiological responses of Holstein heifers. J. Dairy Sci. 102:6639-6648. doi:10.3168/jds.2018-15245.

Weigel, K.A., P.C. Hoffman, W. Herring, and T.J. Lawlor. 2012. Potential gains in lifetime net merit from genomic testing of cows, heifers, and calves on commercial dairy farms. J. Dairy Sci. 95:2215-2225. doi:10.3168/jds.2011-4877.

Yuan, S., A. Schuster, C. Tang, T. Yu, N. Ortogero, J. Bao, H. Zheng, W. Yan. 2015. Sperm-borne miRNAs and endo-siRNAs are important for fertilization and preimplantation embryonic development. Development. 143:635–647. doi:10.1242/dev.131755.


Land Grant Participating States/Institutions


Non Land Grant Participating States/Institutions

Log Out ?

Are you sure you want to log out?

Press No if you want to continue work. Press Yes to logout current user.

Report a Bug
Report a Bug

Describe your bug clearly, including the steps you used to create it.