Using AI Young Sires in Your Herd: Some Genetic and Economic Considerations

Can we predict what a young sire’s proof will be before he has milking daughters? Afrequent argument made against using a young sire is that we don’t know what his production proof will be until after he has milking daughters. This is not entirely true. AI organizations select young sires for progeny sampling based on pedigree merit. One common measure of pedigree merit is parent average. A bull’s parent average is calculated as one-half of his sire’s Predicted Transmitting Ability (PTA) plus one-half of his dam’s PTA for a particular trait. Although parent average is a good predictor of the bull’s eventual proof, we know that some young sires will come through with proofs below their parent average, while others will come through with higher proofs. The net result is that the average proofs for a group of bulls is usually quite close to the overall average of the bulls’ parents. How good a predictor is parent average? In Figure 1, the July 1991 USDA sire summary for Holsteins is used to compare the bulls’ PTAs for milk with their parent averages. The bulls in the comparison were born in 1985, but due to recent major changes in genetic evaluation procedures, (particularly the incorporation of the animal model in 1989) using parent averages from 1985 is not valid. Although there is some overlap between a bull’s current parent average and production proof which reduces the size of the difference, the general relationship still exists. Figure 1 examines 158 bulls with parent averages between 950 and 1050 pounds. The average of the parent average for milk was 1000 pounds. Although all bulls had similar pedigree expectations, actual PTAs for milk ranged between -371 pounds and +1713 pounds, a difference of 2084 pounds. However, the average PTA milk for these 158 bulls is +1002 pounds, only two pounds higher than the average of the parent average. As Figure 1 shows, PTA milk values are evenly distributed above and below parent average. Using a group of young sires minimizes the risk of having daughters from only those bulls with PTA milk values below parent average. Using AI Young Sires in Your Herd: Some Genetic and Economic Considerations