Estimation of Breed-Specific Heterosis Effects for Birth, Weaning and Yearling Weight in Cattle

Genetic selection decisions are important components of improved beef production efficiency. Exploiting heterosis and breed complementarity can improve economically relevant traits and system efficiency. The objective of the current study was to estimate breed-specific heterosis for the seven largest beef breeds (according to registrations) for birth, weaning and yearling weight. Birth, weaning and yearling weights were recorded for steers, heifers and bulls (n= 6,834) from Cycle VII and advanced generations of the Germ Plasm Evaluation project of the U.S. Meat Animal Research Center. Breeds represented in these data included: Angus, Hereford, Red Angus, Charolais, Gelbvieh, Simmental, Limousin and composite MARC III. Model 1 estimated heterosis assuming different levels within and between biological types (British or Continental). Model 2 estimated breed-specific heterosis (a different level of heterosis for each pair of breeds). Heterosis was assumed proportional to expected breed heterozygosity. Direct heritability estimates (SE) for birth, weaning and yearling weight for Model 1 were 0.42 (0.04), 0.22 (0.03) and 0.39 (0.05), respectively. The direct heritability estimates (SE) for Model 2 were the same as Model 1 except yearling weight heritability was 0.38 (0.05). There were differences in levels of heterosis based on biological type (Model 1) and breed (Model 2). Model 1 results for the British x British (BxB), British x Continental (BxC) and Continental x Continental (CxC) heterosis estimates for birth weight were 0.47 (0.37), 0.75 (0.32) and 0.73 (0.54) kg, respectively. The BxB, BxC and CxC heterosis estimates for weaning weight were 6.43 (1.80), 8.65 (1.54) and 5.86 (2.57) kg, respectively. Yearling weight estimates for BxB, BxC and CxC heterosis were 17.59(3.06), 13.88 (2.63) and 9.12 (4.34) kg, respectively. Breed differences exist and can lead to varying levels of heterosis. Specific estimates of heterosis could be useful when selecting breeds for a crossbreeding system and developing composite populations for various production environments and could be useful in multibreed evaluations as heterosis and breed differences are needed to accurately adjust records to produce genetic predictions. Advisor: Matthew L. Spangle