Genotype-Sex Interactions in Sheep

Heritability estimates were calculated for 11 traits in rams and ewes of Rambouillet and Romnelet sheep. The traits were birth weight, weaning weight, average daily and total post-weaning gain, final weight, feed efficiency, grease and clean fleece weight, staple length, wool grade and wool yield. None of the estimates between the two sexes differed significantly. Genotype-sex interaction in each trait and within breed was tested by a statistical model in which effects of year, age of dam, type of rearing, sex, sire and all first order interactions of sex with the remaining factors were included. No significant genotype-sex interaction was detected in either breed. The genetic correlations between the two sexes were very close to unity in 18 of the 22 traits in the two breeds. Only the correlations for birth weight, grease fleece weight and clean fleece weight in Rambouillet and feed efficiency in Romnelet appeared to deviate markedly from unity. Thus it appears that genotype-sex interactions are not important in these groups of sheep.