A genetic analysis of relationships among rates of growth, rate of maturing, body size and productivity in beef cattle

Abstract

Lifetime records of body weight and age at puberty of 215 straightbred and reciprocally-crossed Hereford, Angus and Shorthorn cows collected at the Fort Robinson Beef Cattle Research Station were utilized in a study of maturing patterns. Body weight and degree of maturity (u) of body weight at birth, weaning, 396 days, 550 days, 3 1/3 years, 4 years, puberty and maturity and absolute growth rate (AGR), absolute maturing rate (AMR) and relative growth rate (RGR) over various age intervals were examined. The objecties of this study were 1) to determine heritabilities, genetic and phenotypic correlations and heterosis for the above traits, 2) to characterize samples of the Hereford, Angus and Shorthorn breeds and their crosses for these traits and 3) to examine the potential of altering maturing patterns either by selection or by crossbreeding. Mature weight (MW), which is necessary to calculate u and AMR, was estimated by the average of winter weights at 5 and 6 years of age. Heritability estimates were 0.42 for MW and from 0.65 to 1.02 for immature weights. The estimated genetic correlations were large among all weights and were greater than one between MW and each of the immature weights except those at birth and puberty.