Interbreed Matings in Dairy Cattle. IV. Growth Rate of Two-Breed Crosses

Abstract

Body weights for all single crosses among Ayrshires, Brown Swiss, and Holsteins were compared to those of contemporary purebreds in six periods: birth to 6 months, 7 to 12, 13 to 16, 17 to 21, 22 to 24 months, and in first lactation. Least-squares techniques were used to estimate the effects of year-parity, season, breed groups, age, and the two-factor interactions with the linear and quadratic age effects. Year-parity had a significant influence on weights up to 12 months but not thereafter. Differences among purebreds were important at all ages. General combining abilities differed (P<.05) in all precalving periods, with Holsteins best and Ayrshires poorest; maternal influences were not significant except for birth weight. The average percentage deviation from the parental mean for two-breed crosses was −1.9, 1.6, 2.9, 3.3, 4.1, 3.4, and 3.3 at birth, birth to 6 months, 7 to 12, 13 to 16, 17 to 21, 22 to 24 months, and in first lactation, respectively. Thus, crossbreds gained faster relative to the mean of parental breeds with advancing age up to 21 months. Heterosis for birth weight was negative in three crossbred groups (−1 to −8%) and 0 to 2.7% in the others. There was an average advantage of about 12 kg per female at 16 months of age from crossbreeding, but even where size might be used as the basis of first breeding, crossing among these three breeds should not materially reduce the age at first breeding. The crossbreds did not usually exceed purebred Holsteins in body weight.