Reproductive performance and genetic parameters in first cross ewes from different maternal genotypes

¹ The Australian Sheep Industry Cooperative Research Centre, NSW Department of Primary Industries, Orange Agricultural Institute, Orange, NSW 2800, Australia
² Department of Primary Industries, Primary Industries Research, Rutherglen, Vic. 3685
³ Hamilton, Vic. 3300, Australia

^* To whom correspondence should be addressed. E-mail: neal.fogarty{at}dpi.nsw.gov.au.

	Abstract

The reproduction of 2,846 crossbreed ewes with 7,899 records is reported. The ewes were progeny of mainly Merino dams and 91 sires from several maternal sire breeds including Border Leicester, East Friesian, Finnsheep, Coopworth, Corriedale, Booroola Leicester and several others. There were 3 cohorts of ewes at each of 3 sites that were joined naturally to meat rams for each of 3 years to evaluate reproduction and lamb production. At 2 sites the ewes were joined in the autumn, first at 7 months of age and at 2 sites the ewes were joined in the spring, first at 14 or 17 months of age. The cohorts of ewes and sites were genetically linked by 3 common sires. Mixed linear models were used to analyze ultrasound scanned pregnancy, fetal number, fertility (ewes lambing), litter size, lamb survival, number of lambs born (NLBj), weaned (NLWj) and total weight of lamb weaned (TWWj) per ewe joined. Fixed effects included, sire breed (1 to 10), environment (1 to 4, site and season of joining: autumn, spring), joining (1 to 3), cohort (1 to 3) and interactions. REML procedures were used to estimate (co)variance components. Ewe sire breed effects were significant (P < 0.01) for all the reproduction traits and breed means ranged from 0.75 to 0.96 for fertility, 1.22 to 2.08 for litter size, 0.70 to 0.90 for lamb survival, 0.99 to 1.66 for NLBj, 0.87 to 1.26 for NLWj and 22.9 to 33.8 kg for TWWj, with the ranking of sire breeds varying for different traits. For all traits except lamb survival the contrast between joining 1 vs. 2 and 3 was considerably greater than the contrast between joining 2 vs. 3, with significant environment x joining interactions (P < 0.01). Estimates of heritability for the components of reproduction ranged from 0.03 ± 0.02 for lamb survival to 0.19 ± 0.05 for litter size and those for the composite traits were 0.17 ± 0.04 for NLBj, 0.13 ± 0.04 for NLWj and 0.17 ± 0.04 for TWWj, with repeatability ranging from 0.10 to 0.19. Genetic and phenotypic correlations among the traits are reported. The significant variation among sire breeds of the crossbred ewes can be used to improve reproduction, although there was change in the rank of the breeds for the various traits. There was considerable overlap between the breeds and additional improvement could be achieved by exploiting the genetic variation between sires within breeds for all the ewe reproduction traits.

Key Words: Ewes, heritability, genetic correlations, maternal breeds, lamb production