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Estimation of Variance and Covariance Components to Determine Heritabilities and Repeatability of Weaning Weight in American Simmental Cattle¹

Cornell University² Ithaca, NY 14853

Abstract

Components of (co)variance for weaning weight were estimated from field data provided by the American Simmental Association. These components were obtained for the observational components of variance corresponding to a sire, maternal grandsire, and dam within maternal grandsire model. From these estimates, direct additive genetic variance (²_A), maternal additive genetic variance (²_M), covariance between direct and maternal additive genetic effects (_AM), variance of permanent environment (²_pe) and temporary environment variance (²_te) were determined. A procedure to approximate restricted maximum likelihood (REML) estimates of the observational components of variance based on the expectation-maximization (EM) algorithm is described. From these results, phenotypic variance (²_P) of weaning weight was 667.88 kg². Values for ²_A, ²_M, ²_pe and ²_te were 79.30, 58.38, 49.45, and 469.97 kg², respectively. Genetic correlation between direct and maternal additive genetic effects was .16.

¹ This research was supported by a grant from the Am. Simmental Assoc., Bozeman, MT.

² Dept. of Anim. Sci.