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Virginia Cooperative Extension - Knowledge for the CommonWealth

"My best cow was by a herd bull"

Dairy Pipeline: October 2005

Bennet Cassell Extension Dairy Scientist, Genetics and Management

I have heard this comment from a number of dairy producers through the years and there actually is a sound genetic principal behind it. This isn't the most quantitative evaluation that could be made. It is usually a subjective recollection of an older cow or two that left a favorable impression on the owner. It wouldn't hurt to recall how many half sisters to those cows had been culled years earlier for one reason or another. However, the comment is about "my best cow", not "the best group of cows any bull ever left in my herd." The sound genetic principal comes from selection intensity. A lot of producers use too many different AI bulls, with only enough semen on any one AI bull to produce a few daughters. A herd bull, on the other hand, may breed 30 to 40 heifers a season plus some clean-up duty in the milking herd. Such bulls may produce 20 to 30 daughters in a 150 cow herd. Let's not be too distracted by the decision to make greater use of bulls about which much less is known. The best individual cow out of a group of 30 is almost certain to be at least competitive with, if not better than the best cow out of a group of five daughters of even the top AI bulls. Bulls should be evaluated on the AVERAGE merit of their progeny, not by a subjective evaluation of their best single daughter in one herd. Every daughter a bull leaves in a herd generates income and expenses. The research on this topic is conclusive: daughters of good AI bulls leave the bank account in better shape than daughters of herd bulls. A 2002 study in the Journal of Dairy Science (JDS 85:3492-3502) showed that average daughters of proven AI bulls generated $148 per cow more lifetime net income than average daughters of non-AI bulls under fluid milk market conditions. That's dollars left over after all the bills and receipts - feed, rearing, health, breeding, culling and production - were considered. The "best" cow in a dairy farmer's herd may have been a daughter of a herd bull, but for the vast majority of herds, the best groups of cows were sired by AI bulls.

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