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Postinflection Growth in Straightbred and Crossbred Cattle. I. Heterosis for Weight, Height and Maturing Rate¹

Texas A&M University and Texas Agricultural Experiment Station, College Station 77843

Abstract

Records on 397 cows of the Angus, Brahman, Hereford, Holstein, Jersey breeds and the 10 possible two-breed crosses, reciprocals pooled, were analyzed to evaluate the effects of heterosis on size and maturing rate parameters. Measurements used for analysis were weight, hip height and condition scores taken at quarterly (3-mo) intervals from 9 through 66 mo of age. Breedtype means and heterosis were derived for parameters of Brody's postinflection growth equation, Y_t = A–Be-^kt, fitted for both weight and height, each by two separate methods. One method involved fitting the equation to each individual animal weight-age and height-age record and then using a least-squares analysis of variance to estimate breedtype parameter means. The second method consisted of calculating a least-squares mean weight and height at each age point for each breed type and then fitting Brody's equation to the composite weight-age or height-age record for each breed-type. The results of analyses by each method were similar. Overall, heterosis for asymptotic weight and height were positive (P<.01); weight tended to exhibit higher levels of heterosis than height (6.2 ± 1.4 vs 2.0 ± .4%). Heterosis for weight and height tended to be greater at younger ages than at older ages, although there were no general trends for heterosis in maturing rate as measured by k for either weight or height.

¹ Present address: Farmers Hybrid Companies, Inc., Box 538, Warner, OK 74469.

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