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Using Calving Difficulty Proofs.

Dairy Pipeline: May 1995

by Bennet Cassell
Genetics and Management

Data for calculating calving difficulty proofs are provided by farmers, often as part of their responsibilities as "cooperator herds" in sampling young sires. These proofs have been sponsored by the AI industry since 1977, and are intended to encourage greater use of AI Holstein bulls in breeding heifers. Calving difficulty is scored into one of five categories: no problem, slight problem, needed assistance, considerable force, and extreme difficulty. About 28% of all male births in Holstein heifers need assistance compared to 16% of female births. As cows age, dystocia problems decline and only about 10% of male births require assistance at third parity. Calving difficulty proofs are calculated at Iowa State University using technology especially developed for data scored into discrete categories. The proofs are expressed as "Expected percent of difficult births in heifers" and range from about 5 (the most favorable percentage) to 18% for sires whose progeny are born with greatest difficulty. We measure the direct effect of a sire, that is, his role in the difficulty with which his own progeny are born. We do not publish "maternal dystocia" proofs, which measure the difficulty a bull's daughters have giving birth. This past January, almost 400 active AI Holstein bulls in major US bull studs had dystocia proofs. Of these, 206 had proofs of 9% or lower. These bulls averaged 1246 lbs PTA milk. The remaining bulls, those with proofs of 10% or more, averaged 1193 for PTA milk. I recommend using bulls with proofs of 9 or lower on heifers and reserving semen on bulls with higher dystocia proofs for use on older cows. Do not eliminate bulls with proofs over 9% from the herd breeding program. Many of the top genes for production and other traits can be found in such bulls. Use dystocia proofs to choose service sires for heifers, but find use for the top sires that don't qualify for use on heifers in the milking herd.

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