Variance component and heritability estimates of early growth traits in the Elsenburg Dormer sheep stud

Abstract

A total of 8909 birth weight and 7740 weaning weight records, from the progeny of 215 sires, collected from 1943 to 1990 from the Elsenburg Dormer sheep stud, were analysed. Additive genetic variance and heritability estimates for birth weight (BW), weaning weight (WW), average daily gain (ADG) and the Kleiber ratio (KL) were obtained by Restricted Maximum Likelihood (REML) procedures fitting three different models. Estimates were severely biased upwards when an animal model, ignoring maternal effects, was fitted. A sire model yielded more realistic estimates of direct additive variance. Estimates of maternal genetic variance and corresponding heritabilities (h²_m) were higher than estimates for direct additive variance and heritability (h²_a) when fitted simultaneously in an animal model. The genetic correlations between direct and maternal influence were consistently negative but the proportion of cov (a, m) to phenotypic variance decreased from birth to weaning. The heritability estimates were as follows: BW = 0.12, 0.42, 0.16, 0.43; WW = 0.12, 0.34, 0.13, 0.20; ADG = 0.13, 0.31, 0.13, 0.18; KL = 0.13, 0.26, 0.14, 0.14 for a sire model, animal model, animal model direct effects (h²_a) and animal model maternal effects (h²_m), respectively.

'n Totaal van 8909 geboortegewig- en 7740 speengewigrekords van die nageslag van 215 ramme, wat vanaf 1943 tot 1990 by die Elsenburg Dormerskaapstoet ingesamel is, is ontleed. Additiewe genetiese variansie en oorerflikheidsberamings van geboortegewig (GW), speengewig (SW), gemiddelde daaglikse toename (GDT) en die Kleiberverhouding (KV) is met behulp van Beperkte Maksimum Aanneemlikheid(REML)-prosedures beraam deur drie verskillende modelle te pas. Beramings was onrealisties hoog met die passing van 'n dieremodel ('animal model') sonder moedereffekte. Meer realistiese beramings van direkte additiewe variansie is met behulp van 'n vaarmodel ('sire model') verkry. Beramings van maternale genetiese variansie en ooreenstemmende oorerflikhede (h²_m) was hoër as dié van direkte additiewe variansie en oorerflikheid (h²_a). Die genetiese korrelasies tussen direkte invloed en moederinvloed was deurgaans negatief, maar die proporsie van maternale genetiese variansie tot fenotipiese variansie het van geboorte tot speen afgeneem. Die beraamde oorerflikhede (h²) was soos volg: GW = 0.12, 0.42, 0.16, 0.43; SW = 0.12, 0.34, 0.13, 0.20; GDT = 0.13, 0.31, 0.13, 0.18; KV = 0.13, 0.26, 0.14, 0.14 vir 'n vaarmodel, dieremodel en dieremodel met moedereffekte (h²_a en h²_m), onderskeidelik.

Keywords: Dormer sheep, heritability, maternal effect, REML, variance components