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Genetic and Maternal Effects on Preweaning Growth and Type Score in Beef Calves^{1, 2,}

North Carolina State University, Raleigh 27607

Abstract

Phenotypic and genetic parameters were estimated for birth weight, weaning weight and type score from data collected on beef cattle at four North Carolina locations from 1952 through 1968. These data represented records of 1692 progeny of 48 sires. Data of paternal half-sibs were analyzed according to a least-squares linear model which included effects due to location, year, sex, age of dam, sires nested within year and regression on date of birth or age at weaning. All environmental factors were significant (P<.01). The heritabilities obtained were: birth weight, 0.67; weaning weight, 0.50; type score, 0.36.

In addition, the genetic variance of each trait was estimated by the methods of maternal half-sibs and dam-offspring regression. In order to estimate five causal components of variance and covariance, i.e., direct additive genetic variance, additive genetic variance for maternal effects, genetic covariance between direct and maternal effects, permanent environmental maternal variance and random environmental variance, the dominance deviations were assumed to be unimportant and eliminated from consideration. Also, it was necessary to assume hypothetical ratios between the maternal genetic and the maternal permanent environmental variance. Sizable maternal components of variance and negative genetic covariances between direct effects and maternal effects were detected in all traits.

¹ Paper No. 3255 of the Journal Series of the North Carolina State University Agricultural Experiment Station, Raleigh.

² Computing services for this invesetigation were supported by Public Health Service Grant FR-00011.

³ Present address: Research Station, Lethbridge, Alberta.