Moment-type Estimation of Genetic Parameters and their Variances for Calving Date and Production Traits from Hereford data using Multi-Way Models
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Factors influencing growth traits as calf, and as dam traits have been analysed. Adjustment factors for such factors were obtained using Least Squares procedure, and used to correct records used in parameter estimation. All records were corrected for sex of calf, age of dam, and season of birth. Heritability estimates for calf traits were .61±.14, .32±.07, .38±.09, .43±.14, .70±.17, respectively, for birth weight, preweaning average daily gain (ADG), 205-d weaning weight, postweaning ADG, and 365-d yearling weight. Corresponding estimates foi dam traits were .56±.22, .48±.11, .53±.20, .46±.15, .66±.30. Within-herd repeatability estimates were .31, .35, .37, .18, .24, respectively, for dam traits. Genetic correlations among traits were generally higher than corresponding phenotypic correlations. All direct-maternal correlations of calf traits were negative: birth weight (-.21); 205-d weaning weight (-.58); and yearling weight (-.57). The porportion of maternal (to phenotypic) variance was higher among traits known to be under large maternal influence (birth weight, .09; preweaning ADG, .05; weaning weight, .07) than the other traits (postweaning ADG, .01; yearling weight, .01). Calving date was suggested as a measure of reproductive performance. Weight of calf, age of dam, weight of dam, initial and previous calving dates, and milk production potential were found to be significantly associated with calving date. Calving date was found to significantly affect weight and age at weaning, age at which yearling weights were measured, and postweaning ADG. Heritability and within-herd repeatability of calving date was estimated at .19±.06, and .09, respectively. A method for estimating standard errors of variance ratios, using logarithmic transformation of the ratios, was proposed and used in this study.