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Virginia Cooperative Extension - Knowledge for the CommonWealth

How much genetic change are we making?

Dairy Pipeline: February 2001

Bennet Cassell
Extension Dairy Scientist, Genetics and Management

Like everything else in the dairy business, the cows are changing! Dairy producers are frequently reminded to update their sire selection standards to keep up with genetic progress. Just how rapid is that change? I checked the tables of breeding values on the USDA website and came up with some estimates. These trends are for the last 10 years. We can expect similar improvement for the next five years or so, but predictions beyond that point are premature. Fastest change for milk is in the Holstein breed, where PTA's for cows are increasing by 113 lbs./year. The breed with the next most rapid change in milk is Brown Swiss (101 lbs./year), but Jerseys are close behind at 96 lbs./year. Change in milk for Guernseys is 87 lbs./year, while Ayrshires are improving by 59 lbs./year. Estimates of genetic trend don't vary as much from breed to breed for fat and protein, ranging from a low of 2 lbs. improvement per year for protein for Ayrshires to a high of 4 lbs. improvement per year in Brown Swiss for fat. Keep in mind that milk components have direct value in many milk markets, and that changes in milk marketing systems may affect the rates of genetic change for milk components in the coming years. A change of 113 lbs./year in PTA for milk in Holsteins means that selection standards have to go up every year to insure that the best bulls are used. The mental math required to do this consistently isn't necessary. A better way is to stick with Rank Percentiles for a composite index like Net Merit. USDA publishes that percentile with every bull's genetic evaluation. If you always use bulls in the top 20% heavily (bulls above the 80th percentile for Net Merit), you won't have to worry about genetic trend for any of the traits. The ranking procedure takes care of genetic trend automatically. Make sure your selection program keeps pace with genetic trend.

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