Submitted to: Book Chapter
Publication Type: Proceedings
Publication Acceptance Date: 10/22/2003
Publication Date: 12/15/2003
Citation: Van Raden, P.M. 2003. Genetic evaluations for fitness and fertility in the United States and other nations. Proceedings of National Genetics Workshop, Raleigh, North Carolina, October 20-21, 2003. p. 103-106. Interpretive Summary: Progress to increase the ability of dairy cattle in the US to be more fertile, yet more productive has slowed because of an antagonistic relationship between the two objectives. Generally speaking, as milk production goes up, cows are less able to reproduce. Variation expressed by fertility traits is much greater than production traits, making predictions of genetic expression more difficult and less accurate. In addition to difficulties in evaluating fertility traits, differences arise comparing US traits to international traits because of measurement on different scales or interpretations of the traits. However, US evaluations for economically important traits are more similar to traits evaluated in European countries than they are to themselves, suggesting that US evaluations are useful in comparing international dairy cattle. In February 2003, daughter pregnancy rate was introduced as a measure of cow fertility. A predicted transmitting ability of 1% higher pregnancy rate is equivalent to 4 fewer days open. Fertility evaluations differ greatly across nations, but US daughter pregnancy rate had the highest correlation with UK calving interval in a recent study. In August 2003, the Net Merit formula (ranking index for US evaluations) was revised to include daughter pregnancy rate and calving ease. The revised index will allow producers to reduce costs of infertility and difficult births while increasing income and profit through production.
Technical Abstract: Coefficients of variation for genetic and phenotypic expression of fitness and fertility traits are higher than those for type and yield traits. Because selection for individual traits may result in greater genetic progress than for composite traits, new methods to estimate the heritability of fitness traits such as Daughter Pregnancy Rate and service sire calving ease are being estimated for use in Net Merit calculations. However, because fertility traits are measured differently in other countries included in Interbull, some estimate as to the correlations of fertility traits should be attempted across participating nations. In a recent study, US pregnancy rate correlated most highly to the UK calving interval. Production, conformation, longevity, udder health, and calving ease traits evaluated in the US correlated more highly with those of other Interbull participating nations than the other countries correlated with each other. This is surprising given the close proximity of the European members to each other, sharing environment more closely than the US to any nations included. Official evaluation of fertility traits began in February 2003 and revision of the Net Merit formula to include DPR, service sire calving ease and daughter calving ease occurred in August 2003. The revision should help reduce the costs of reduced fertility for producers, while increasing production and profits.