|Miller, Robert - Bob|
Submitted to: Journal of Dairy Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/20/2004
Publication Date: 7/1/2004
Citation: Van Raden, P.M., Sanders, A.H., Tooker, M.E., Miller, R.H., Norman, H.D., Kuhn, M.T., Wiggans, G.R. 2004. Development of a national genetic evaluation for cow fertility. Journal of Dairy Science. 87(7):2285-2292. Interpretive Summary: Selection for high milk yield over several generations of dairy cows has contributed to a decline in cow fertility because of the unfavorable genetic correlation between these two traits. The purpose of this paper was to examine several measures of reproductive success and introduce a U.S. national genetic evaluation for cow fertility. A national evaluation was developed for daughter pregnancy rate (DPR), which measures the percentage of non-pregnant cows that become pregnant within each 21-day opportunity period. Cow fertility was negatively correlated with yield but is a major component of longevity. Thus, recent selection for longevity may have slowed the long-term decline in fertility. Direct selection on cow fertility could halt or reverse the decline thereby increasing profitability for dairy producers. National DPR evaluations are calculated through the Animal Improvement Programs Laboratory (AIPL) of USDA national database with over 16 million cows for over 40 million calvings since 1960 and include limited cow fertility traits. A more complete database with additional fertility and reproductive traits was developed in conjunction with this research and will allow a more precise modeling of fertility in the future.
Technical Abstract: A national evaluation was developed for pregnancy rate, which measures percentage of nonpregnant cows that become pregnant within each 21-d opportunity period. Data for evaluation are days open calculated as date pregnant minus calving date. Date pregnant is determined from last reported breeding or from subsequent calving minus expected gestation. Success or failure of last breeding can be confirmed by veterinary diagnosis or a report that the cow was sold because of infertility. Fertility records are considered complete at 250 d in milk, and lower and upper limits of 50 and 250 d are applied to days open. Data are adjusted for parity and calving season within geographic region and time period and evaluated with an animal model. For calculation of genetic evaluations, days open are converted to pregnancy rate by the linear formula pregnancy rate = 0.25 (233 - days open). Evaluations are expressed as predicted transmitting ability for daughter pregnancy rate. Genetic correlations among several fertility measures and other evaluated traits were estimated from three large data sets. Correlation with days open was less for nonreturn rate than for days to first breeding, probably because nonreturn rate had lower heritability. Cow fertility was negatively correlated with yield but is a major component of longevity. Thus, recent selection for longevity may have slowed the long-term decline in fertility. Direct selection for fertility could halt or reverse the decline.