Estimation of direct and maternal additive and heterotic effects for measures of size, growth and maturing pattern in cattle

Abstract

Measurements of body weight and hip height at immature ages, including puberty, and at maturity and age at puberty on 644 cows were used in a study of the genetic effects associated with heterosis on measures of size, growth and maturing pattern. The cows were samples of the five breeds (Angus, Brahman, Hereford, Holstein and Jersey) represented in a five-breed diallel experiment conducted at the Texas A&M Agricultural Research Center at McGregor. Direct additive effects of Brahman and Holstein were larger and those of Jersey were lower than Angus direct additive effects for body weight at immature ages and maturity. Maternal additive effects for body weight at immature ages for Brahman, Hereford, Holstein and Jersey were generally not significantly different from those of Angus. Average direct heterosis estimates for body weight at ages prior to maturity ranged from 2.34 to 5.02%. Average maternal heterosis estimates were not significant for body weight at most immature ages studied. Hip height showed a similar pattern in the relative importance of the various genetic effects as that observed for body weight. Average direct heterosis estimates for hip height at immature ages ranged from .83 to 1.94%. Direct additive effects were larger and breed direct heterotic effects were smaller for Brahman and Hereford than those for Angus, Holstein and Jersey for age at puberty.Straightbreds and crossbreds reached puberty at approximately similar degrees of maturity for body weight and hip height. Crossbreds were more mature for body weight and hip height at earlier ages than straightbreds. Positive average direct heterosis estimates were observed only for the younger age intervals for absolute growth rate and absolute maturing rate for weight. Average direct heterosis estimates were negative for relative growth rate for weight for all age intervals. Average direct heterotic effects were generally negative for all measures of growth and maturing pattern for height for most age intervals. Breeds growing to larger mature size tend to show larger breed direct additive and heterotic effects for measures of size and growth at immature ages. Heterosis seems to increase rate of maturing of crossbreds, causing crossbreds to be heavier and more mature and reach puberty at younger ages than straightbreds.