International Cow Fertility Conference Review and Abstract

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Published on: June 17, 2014

I recently had the good fortune of being able to attend the New Science-New Practice Bovine Fertility Conference held by the British Society for Animal Science (BSAS) in Westport, Ireland.  This was an extremely well attended event with an impressive list of over 450 delegates representing countries throughout the world.

There was an international cast of speakers including Stephan LeBlanc, Gabriel Bo, Patrick Lonergan, Stephen Butler, and others and we were well represented from the U.S. by Richard Pursley, Jose Santos, Paul Fricke, Matt Lucy, George Seidel, Peter Hansen, and Milo Wiltbank.

The conference covered all aspects of bovine fertility with a particular emphasis on genetics and reproductive physiology.  A recurring theme throughout the program was the importance of progesterone on multiple aspects of bovine reproduction.  From post-partum estrous dynamics to follicular development and LH pulses, multiple speakers detailed the importance of this hormone both in the main sessions and the ET workshop. With permission from BSAS we have reprinted an abstract (below) from Dr. Wiltbank detailing some of the effects of progesterone on cattle reproduction.

Kevin A. Lindell DVM,MS

Immediate Past President, AETA

Physiological and practical effects of progesterone on reproduction in dairy cattle

M C Wiltbank1, A H Souza1,2, P D Carvalho1, A P Cunha1, J O Giordano1,3, P M Fricke1, G M Baez1, M G Diskin4 1Department of Dairy Science, University of Wisconsin-Madison, Wisconsin USA 2Current Address:  University of California Cooperative Extension, California USA 3Current Address:  Department of Animal Science, Cornell University, New York USA 4Animal and Grassland Research and Innovation Centre, Teagasc Ireland


Implications This reviews the effects of circulating progesterone (P4) on dairy cattle reproduction. Various methods to elevate P4 during growth of the preovulatory follicular wave have been shown to increase pregnancies/AI and reduce double ovulation, providing methods to improve fertility and reduce twinning rate in lactating dairy cattle. Conversely, very low concentrations of P4 near AI are needed to optimize fertility. Finally, elevations of P4 after AI can impact embryonic development and also may elevate fertility. Thus, innovative strategies to optimize circulating P4 concentrations during selected reproductive periods enhance our management tools for improving reproductive efficiency of lactating dairy cows.

Abstract The discovery of progesterone (P4) and elucidation of the mechanisms of P4 action have an important place in the history of endocrinology and reproduction. Circulating P4 concentration is determined by a balance between P4 production, primarily by the corpus luteum (CL), and P4 metabolism, primarily by the liver. The volume of luteal tissue and number and function of large luteal cells are primary factors determining P4 production. Rate of P4 metabolism is generally determined by liver blood flow and can be of critical importance in determining circulating P4 concentrations, particularly in dairy cattle. During timed AI protocols, elevations in P4 are achieved by increasing number of CL by creating accessory CL or by supplementation with exogenous P4. Dietary manipulations can also alter circulating P4, although practical methods to apply these techniques have not yet been reported. Elevating P4 prior to the timed AI generally decreases double ovulation and increases fertility to the timed AI. Near the time of AI, slight elevations in circulating P4, possibly due to inadequate luteal regression, can dramatically reduce fertility. After AI, circulating P4 is critical for embryo growth and establishment and maintenance of pregnancy. Many studies have attempted to improve fertility by elevating P4 after timed AI. Our recent meta-analysis and manipulative study indicated small fertility benefits (3-3.5%) mostly in primiparous cows. Thus, previous research has provided substantial insight into mechanisms regulating circulating P4 concentrations and actions. Understanding this prior research can focus future research on P4 manipulation to improve reproductive success.

Conclusions  This manuscript has attempted to describe the underlying physiology that produces the changes in circulating P4 in lactating dairy cows and the potential reproductive challenges associated with sub-optimal P4 concentrations. Metabolism of P4 appears to be the primary cause of lowered P4 in lactating dairy cows, although increases in P4 production by the CL may be important in higher fertility genotypes of dairy cows. This manuscript reviewed the scientific literature on P4 and fertility with clear evidence for effects of P4 at all three time periods that were analyzed. Prior to AI, there were very dramatic effects observed when the P4 concentrations before AI were compared to subsequent fertility or when manipulative studies were performed to increase P4 before AI. Improvements of more than 10% in P/AI were observed by increasing P4 concentrations. In addition, insufficient P4 at this time may, at least partially, underlie the high double ovulation rate as well as the lowered fertility that is characteristic of high-producing dairy cows. Near the time of AI, it is critical that P4 concentrations reach a nadir concentration. Even small increases in P4 near the time of AI were associated with dramatic reductions in fertility, either in cows bred to natural estrus or after timed AI protocols. Following AI, there are dramatic effects of increasing P4 on embryo elongation. In addition, there have been relationships found between P4 concentrations after AI and subsequent fertility when linear regression analyses were performed.  However, manipulative studies have not provided consistent or dramatic effects of P4 supplementation on fertility in most studies that have evaluated large numbers of cows. Thus, although substantial research has investigated the role of P4 on fertility in lactating dairy cows for more than 6 decades, it seems clear that future research is needed to fully understand the physiology that underlies previous research observations and to unlock the practical improvements in fertility that are expected by consistent management of P4 concentrations in lactating dairy cows.

Full citation: animal / Volume 8 / Supplement s1 / May 2014, pp 70-81

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