Genetic and Environmental Differences Between Registered and Grade Holstein Cows

Abstract

Phenotypic and genetic measures of milk yield were compared for sire-identified registered and grade Holsteins in the United States. First lactation registered cows produced more milk within herd than did grades. Grades were culled more intensely than registered cows, resulting in higher average yield by maturity for remaining grades than for remaining registered cows. Average Cow Index milk was higher overall for grades until 1981. Within herd and year of first calving, registered cows were higher for yield, Cow Index, and sire Predicted Difference since 1974. Analyses for cows alive at a given time or cows with dam Cow Index overestimated grade genetic merit because of differences in selection intensity. No sire identification for two-thirds of grades resulted in substantial data loss and probably over-estimation of grade genetic merit from sire-identified cows. Preferential treatment according to registry status was examined by comparing registered and grade yields within herd, year, and sire. Milk yield of registered cows was 95kg higher than for grade paternal sisters in 1980 to 1984; bias in favor of registered cows was 3kg for Cow Index milk. Bias would be proportional to herdmates of opposite registry status. Average genetic merit of sire-identified registered and grade Holstein cows differed little.