Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/11/2011
Publication Date: 3/17/2011
Citation: Geary, T.W., Abreu, F.M. 2011. Factors affecting fertilization and pregnancy establishment in beef cows. Proceedings of the XV Course on New Approaches to Production and Reproduction in Cattle. Pp. 272-287. Uberlandia, Brazil, March 17, 2011. Interpretive Summary: Fertility is the single most important trait affecting profitability of beef production and embryonic mortality represents the single greatest economic loss for cow/calf producers worldwide. With more than 70,000,000 beef females exposed to breeding each year in Brazil, annual opportunity losses exceed $2.4 billion. In beef cattle, fertilization rates to a single service exceed 90%, but rarely do 65% of matings result in pregnancy establishment and birth of a live calf. This paper helps producers understand the differences between a cow’s estrous cycle and early pregnancy establishment and the obligatory events for pregnancy to be successful. Some of the factors discussed include embryo, dam, sire, and environmental contributions.
Technical Abstract: Embryonic mortality represents the single greatest economic loss for cow/calf producers worldwide. In beef cattle, fertilization rates to a single service exceed 90%, but rarely do 65% of matings result in pregnancy establishment and birth of a live calf. The primary difference between a cow’s estrous cycle and early pregnancy is that the developing embryo in the cow’s uterus must prevent the release of prostaglandin F'' from the uterus approximately 17 d after estrus. This process is referred to as maternal recognition of pregnancy. The embryo must be developing in complete synchrony with the cow’s uterus and produce the compound interferon tau (IFNt) to block prostaglandin F'' release and allow sustained release of progesterone by the ovarian corpus luteum. One of the greatest factors preventing our ability to improve pregnancy establishment is early diagnosis of pregnancy in beef cattle. Currently, we cannot identify pregnancy until d 27 after breeding. However, blood vascularity to the corpus luteum is described in this paper as a new marker of permissiveness to pregnancy establishment. It is highly correlated with blood progesterone concentration and may provide a tool for understanding when most pregnancies are lost. Anything that impedes an embryo’s growth and production of IFNt could disrupt maternal recognition of pregnancy.