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What Makes an AI Bull a Top Sire?

Dairy Pipeline: July 1995

by Bennet Cassell
Genetics and Management

Over 1500 young Holstein bulls are sampled by AI studs each year. Only 10 to 15 of these ever reach the top distinction in AI of being a "sire of sons". Top bulls have unique COMBINATIONS of good genes. Lots of bulls transmit high milk production, but not all of them improve protein as much as they improve milk. Of the protein improving bulls, many have one or more problems with type traits, perhaps siring wide front teats or undesirable foot structure. The AI industry is very selective about sires of sons. Only the best are needed and the best bulls transmit genes for top production AND acceptable udders and feet and legs. Farmers choosing sires of replacement heifers should use the same principles. High production is critical to insure future profitability of commercial operations, but cows must last and avoid mastitis problems. Top sires for this combination of traits will rank at the top on USDA's NET MERIT index. Farmers interested in marketing cattle domestically and abroad will find the TPI list published by the Holstein Association useful in locating bulls with good gene combinations. Semen on top sires (the ones leaving the most offspring in a herd) must be available at a reasonable cost, which means that the desirable gene combinations cannot be so rare that few bulls ever qualify. For instance, a farmer looking for extremely close front teat placement and very high production is asking Mother Nature to produce a cow that makes a lot of milk in a small mammary gland. Expect to pay a lot for bulls with those characteristics and be sure the genetic evaluations are accurate. Nature won't produce such combinations very often. A final requirement for a top sire is that the bull be unrelated or only remotely related to many cows or heifers in a herd. Otherwise, inbreeding problems will limit his usefulness. It takes a lot to be a top sire. I'm glad we have over 1500 choices placed in sampling each year.

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