BREED-DIRECT, BREED-MATERNAL AND NONADDITIVE GENETIC EFFECTS FOR PREWEANING TRAITS IN CROSSBRED CALVES

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Abstract
Two sets of preweaning records of calves were used to estimate breed-direct, breed-maternal, and nonadditive genetic effects. Three groups were represented in both sets of data: a straightbred Hereford line; a rotational crossbreeding line using Angus, Charolais, Hereford, and Simmental breeds; and a rotational crossbreeding line using Angus, Hereford, Holstein-Friesian, and Simmental breeds. Dataset 1 (DS1) consisted of calf records from 1972 to 1976 while dataset 2 (DS2) comprised records from 1978 to 1982. The breeds were the same in both datasets except the Simmental breed was not used in DS1. The traits studied in both DS1 and DS2 were birth weight (BWT), preweaning average daily gain (ADG), and weaning weight (WWT). Calving difficulty (CD) and percent assisted births (%AB) were studied in DS1. A multiple regression procedure was used to estimate breed-direct and breed-maternal effects, as well as average individual and maternal heterosis. Compared to the Hereford breed, breed-direct effects for BWT were negative while breed-maternal effects were positive for all breeds. Estimates of breed-direct and maternal effects for CD and %AB indicated that Simmental breeding would increase dystocia directly, but could decrease dystocia maternally. All breed-maternal effects for CD and %AB were negative compared to the Hereford breed. For ADG and WWT, breed-direct effects for Simmental, Charolais, and Holstein-Friesian were positive in DS2 but Charolais direct effects in DS1 were negative compared to Hereford. Estimates of average individual and maternal heterosis for the traits studied agreed with reported literature values except for weaning weight in DS2, where a large negative estimate (P < 0.10) for average WWT maternal heterosis was obtained. Key words: Beef cattle, crossbreeding, direct effects, maternal effects, heterosis