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Virginia Cooperative Extension - Knowledge for the CommonWealth

Looking ahead to new proofs for fertility and calving ease

Dairy Pipeline: June 2002

Bennet G. Cassell
Extension Dairy Scientist
Genetics and Management
(540) 231-4762

For a number of years, NAAB has coordinated a genetic evaluation called "Percent difficult births in heifers" to help dairy producers choose service sires for heifers. More recently, DRMS Raleigh began to use DHI breeding records to calculate "Estimated Relative Conception Rate", a measure of fertility in AI bulls. Both of these proofs measure the performance of the service sire used in a mating, and are thus "direct" evaluations of the bull involved. However, the cow being bred also has an impact on dystocia and conception. What is the role of her sire, the maternal grandsire of the fetus, in dystocia or conception? Researchers at AIPL and several universities are making progress toward publication of genetic evaluations for calving ease and fertility on maternal grandsires. These new genetic evaluations will be very helpful in managing undesirable genetic changes in dystocia and fertility. A maternal grandsire proof for dystocia, for instance, will help decide if use of a bull as service sire for calving ease produces too many daughters that have difficulty giving birth. We won't see these new proofs for several months or perhaps a year, but it isn't too soon to start learning the terminology. Suggested names for fertility proofs are "Service bull non-return rate", "daughter non-return rate", and "daughter days open". Days open is a new trait related to conception, but calculated from different information. Hopefully, it will confirm what conception evaluations reveal about fertility of a bull. The suggested terms for dystocia proofs are "Service bull calving ease" and "daughter calving ease". The key for producers will be in recognizing the difference between an evaluation of a bull's direct contribution to dystocia or fertility, and his contribution to those same traits through his daughters. Just keep in mind that we have always evaluated milk production on bulls through the performance of their daughters because bulls cannot express milk yield directly. Daughter calving ease, daughter non-return rate, and daughter days open are really no different than daughter milk yield.

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