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ARS Home » Plains Area » Miles City, Montana » Livestock and Range Research Laboratory » Research » Publications at this Location » Publication #334407
Title: Follicle size, endocrine profiles, and pregnancy establishment in beef cows

Author
item DICKINSON, S - University Of Missouri
item Geary, Thomas
item MONNIG, J - University Of Missouri
item POHLER, K - University Of Tennessee
item GREEN, J - University Of Missouri
item SMITH, M - University Of Missouri

Submitted to: Animal Reproduction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2016
Publication Date: N/A
Citation: N/A

Interpretive Summary: Current protocols are very good at synchronizing estrus and ovulation in cattle. This practice allows the use of semen from more valuable bulls to improve calf quality. Using this semen to breed cows is referred to as artificial insemination (AI). Pregnancy rates to timed AI are similar to those obtained by AI after detecting estrus. A small group of cows develop and release an immature egg and have lower fertility. The reasons for reduced fertility have been the focus of our research and the topic of this paper.

Technical Abstract: Reproductive technologies to synchronize estrus and ovulation in cattle have enhanced the ability to practically utilize artificial insemination to increase both genetic merit and reproductive management of beef and dairy herds. The ability to successfully synchronize a follicular wave and ovulation, in heifers and cows, has improved substantially in recent years. Consequently, pregnancy rates to a single fixed-time artificial insemination (FTAI) can approximate that of insemination following spontaneous estrus. Despite these advances, a subset of heifers and cows often have a physiologically immature dominant follicle at the time of GnRH-induced ovulation. These animals will exhibit reduced pregnancy rates and decreased embryonic survival if a pregnancy happens to become established. The physiological mechanisms underlying the preceding decreased fertility has been a focus of our laboratories and may include an effect of the follicular microenvironment on both oocyte competence and the maternal environment. Oocytes must have adequate opportunity to complete cytoplasmic and molecular maturation during the final stages of oocyte maturation that occur within the preovulatory follicle. Follicular status, during the proestrus period, must be such that adequate circulating concentrations of estradiol are present before FTAI to increase oviductal transport of gametes and enhance both the luteinizing capacity of granulosa cells and progesterone receptor population in the post-ovulatory uterus. Following ovulation, the follicle’s transformation to a functional corpus luteum to secrete adequate amounts of progesterone is essential for the establishment of pregnancy. The physiological status of the preovulatory follicle, prior to FTAI, greatly affects the concepts discussed above and has an important impact on pregnancy establishment and maintenance in cattle.