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Dairy Pipeline: October 2002
Bennet Cassell
Extension Dairy Scientist,
Genetics and Management
(540) 231-4762
email: bcassell@vt.edu
The Animal Improvement Programs Laboratory at USDA, Beltsville, MD plans to publish genetic evaluations for female fertility for the first time in February 2003. The trait evaluated will be "pregnancy rate" defined as the percentage of non-pregnant cows that become pregnant in a 21-day period. Pregnancy rate includes estrus expression (and detection, though the cow's genes don't cause that part), ovulation, implantation, and ultimately the ability to carry the fetus into gestation. A pregnancy rate evaluation on a bull measures the genetic ability of his daughters to become pregnant. A typical pregnancy rate proof might be +1.5, which would mean that a particular bull's daughters tend to become pregnant 1.5% more often than an average cow born in the year of the genetic base. Such a bull's daughters would get pregnant 3% more often than another bull with a pregnancy rate evaluation of -1.5%. Pregnancy rate is closely related to days open, as the only way to reduce days open (ignoring VWP) is for cows to become pregnant more quickly. The genetic evaluations for pregnancy rate could be converted to proofs for days open by multiplying the pregnancy rate evaluation by -4. The bull above with the pregnancy rate evaluation of +1.5 would sire daughters that were open on average 6 days less (1.5 X -4 = -6) than an average cow born in the genetic base year. DHI data will be used to calculate the new proofs, and individual cow fertility measures will be verified by a subsequent calving where possible. The USDA files include 36 million lactation records by 14 million cows that have been tested and identified by DHI since 1960.