Weaning weight inheritance in environments classified by maternal weight change

¹ Department of Animal Sciences, Colorado State University, Fort Collins, CO 80523-1171
² Department of Animal Sciences, Colorado State University, Fort Collins, CO 80523-1171; Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand

^* To whom correspondence should be addressed. E-mail: mark.enns{at}colostate.edu.

	Abstract

In good environments, cow intake is sufficient for their own growth and for milk production to support their calf. In poor environments, cows lose weight or may reduce milk supply to maintain themselves. Heritability for direct genetic and maternal components of weaning weight as well as the correlations between these components might be expected to vary according to these circumstances. The purpose of this study was to estimate heritability and genetic correlations for the direct genetic and maternal components of weaning weight classified in two environments according to maternal weight gain and to identify whether or not a single heritability estimate is appropriate for the differing environments experienced by cows from year to year. Data used in this analysis was obtained from the Red Angus Association of America and consisted of 96,064 cow weight observations and 27,534 calf weaning weight observations. A dam's change in weight from one year to the next was used to classify each calf's weaning weight into one of two environmental groups: good or poor. Best linear unbiased estimates of change in cow weight with age were obtained from analysis of cow weight using a repeatability model. If the phenotypic change in cow weight exceeded this average weight change, their calf's weaning weight associated with the end of this time frame was classified as having been observed in a good environment. If not, their calf's corresponding weight was classified as having occurred in a poorer than average environment. Heritability estimates of 0.24 ± 0.03, 0.24 ± 0.03, 0.13 ± 0.02, and 0.14 ± 0.02 were obtained for weaning weight good direct, poor direct, good maternal and poor maternal, respectively. Correlations between direct genetic and maternal weaning weight components in the good and poor environments were -0.47 ± 0.08 and -0.20 ± 0.09, respectively. These variance components are not sufficiently distinct to warrant accounting for dam nutritional environment in national cattle evaluation.

Key Words: beef cattle, heritability, weaning weight, environment

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