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Relationships Between Sire Evaluations at Different Herdmate Levels

Animal Husbandry Research Division, USDA, Beltsville, Maryland

ABSTRACT

Relationships between independent measures of a bull's breeding value at different levels of herd production were investigated. The data consisted of the 2 times, 305-day, mature equivalent (ME) first lactation records of the artificially inseminated (AI) progeny of 40 Holstein sires. Each bull had 1,000 or more daughters. Progeny were classified into one of four groups, based on milk yield level of herdmates (I = 4,536–5,442 kg; II = 5,443–6,349 kg; III = 6,350–7,256 kg; and IV = 7,257–8,164 kg). Daughter averages rose with increases in herdmate level, while the magnitude of the Predicted Difference measure of a sire's breeding value decreased 289 kg (103, 47, –39, and –186 kg, respectively) from low (I) to high (IV) herdmate levels.

Correlations among sire progeny averages at the different herdmate levels were all very high (0.88 to 0.96) and indicated that bulls ranked in about the same order at all levels. Regressions computed in the same manner indicated the absence of a one-for-one relationship in the magnitude of measures of breeding value at the different herdmate levels. The Predicted Difference measure of a sire's breeding value only partially accounted for variation in herdmate milk yields among sires. It was an effective criterion for ranking bulls evaluated within the same herd levels, but somewhat less effective in establishing absolute breeding merit. The maximum bias in predicted differences of bulls with very high yielding herdmates (6,800 kg of milk or more) was about 5 to 10%.