Assessing Wiltshire Horn-Merino crosses. 2. Reproductive traits

Abstract

Wiltshire Horn-Merino (WH-M) crosses of 1/2, 5/8 and 31/4 Merino content were compared for various reproductive traits over an 8 year period. For 3 years pure Merinos were also included in the comparison. Merino ewes were of lower fertility and fecundity than the 1/2 Merino WH-M ewes. For example, numbers of ewes lambed per 2-year-old ewes joined were 2.6-15% lower for Merinos. For fecundity in 3-year-olds, litter sizes for Merino ewes averaged 0.33 lambs fewer than for 1/2 Merino WH-M. Among the WH-M ewes, fertility was uniformly high for all genotypes. Fecundity was considerably higher for 1/2 Merinos than for the 5/8 and 3/4 Merinos. There was no evidence of a difference in fertility or fecundity between F1 and later-generation 1/2 Merinos, and hence no evidence of heterosis. In 2 severe drought years the lambing percentages decreased most in the more productive ewes (1/2 Merinos and older ewes). Genotypes and age groups were more similar than in non-drought years, although a significant effect of genotype was still present in all years.