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ID is key to avoid inbreeding.

Dairy Pipeline: June 1996

by Bennet Cassell
Extension Dairy Scientist
Genetics and Management
Virginia Tech

The January 1996 sire summary included 604 active AI Holstein bulls. Of these, 123 were sons of Blackstar, 61 were sired by Mark, and 54 were Cletius sons. Closer relationships between animals in a population is a natural byproduct of careful selection. As we seek to breed more profitable cattle, we make heavy use of a few carefully chosen individuals. Up until now, the economic incentives to offer outcross bulls in AI have not been strong enough to offset the costs (lower genetic merit and consequently lower demand for semen). While that may change in the future, dairy farmers need to recognize that inbreeding is a more demanding problem in Holsteins than it was 10 years ago. Matings within a herd can be arranged to use the best of those 123 Blackstar sons and avoid most major inbreeding problems. The critical piece of information necessary, however, is sire identification of cows being mated. In the past, farmers have been encouraged to identify their cows by sire so genetic evaluations could be calculated. Many farmers questioned the record keeping costs and benefits and simply ignored identification on a high percentage of animals in their herds. With today's potential for inbreeding, good identification has a very direct economic benefit to individual farmers which wasn't so obvious several years ago. Each 1% increase in inbreeding reduces milk yield by 65 lbs of milk per 305 day lactation according to a recent study. Mating a Blackstar son to a Blackstar daughter generates at least 12.5% inbreeding for a loss of over 800 lbs of milk per lactation. This loss only applies to those offspring surviving to calve and does not cover embryonic and calfhood death losses, reduced gains, and infertility in heifers. If your DHI records show fewer than 90% of cows identified by sire (state average is 78%), chances are that you will experience some accidental inbreeding losses in the years to come unless record keeping improves. Give some thought to changing your record system, calf tagging practices, or priority for good ID with this fall's calf crop. You will need good ID even more by the time those heifers are ready to breed than you need it now.

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