Genetic parameters for wool traits, live weight, and ultrasound carcass traits in Merino sheep.

Genetic correlations between 29 wool production and quality traits and live weight and ultrasound fat depth (FAT) and eye muscle depth (EMD) traits were estimated from the Information Nucleus (IN). The IN comprised 8 genetically linked flocks managed across a range of Australian sheep production environments. The data were from a maximum of 9,135 progeny born over 5 yr from 184 Merino sires and 4,614 Merino dams. The wool traits included records for yearling and adult fleece weight, fiber diameter (FD), staple length (SL), fiber diameter CV (FDCV), scoured color, and visual scores for breech and body wrinkle. We found high heritability for the major yearling wool production traits and some wool quality traits, whereas other wool quality traits, wool color, and visual traits were moderately heritable. The estimates of heritability for live weight generally increased with age as maternal effects declined. Estimates of heritability for the ultrasound traits were also higher when measured at yearling age rather than at postweaning age. The genetic correlations for fleece weight with live weights were positive (favorable) and moderate (approximately 0.5 ± 0.1), whereas those with FD were approximately 0.3 (unfavorable). The other wool traits had lower genetic correlations with the live weights. The genetic correlations for FAT and EMD with FD and SL were positive and low, with FDCV low to moderate negative, but variable with wool weight and negligible for the other wool traits. The genetic correlations for FAT and EMD with postweaning weight were positive and high (0.61 ± 0.18 to 0.75 ± 0.14) but were generally moderate with weights at other ages. Selection for increased live weight will result in a moderate correlated increase in wool weight as well as favorable reductions in breech cover and wrinkle, along with some unfavorable increases in FD and wool yellowness but little impact on other wool traits. The ultrasound meat traits, FAT and EMD, were highly positively genetically correlated (0.8), and selection to increase them would result in a small unfavorable correlated increase in FD, moderately favorable reductions in breech cover and wrinkle, but equivocal or negligible changes in other wool traits. The estimated parameters provide the basis for calculation of more accurate Australian Sheep Breeding Values and selection indexes that combine wool and meat objectives in Merino breeding programs.

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

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 bred naturally to meat-type rams for each of 3 yr to evaluate reproduction and lamb production. At 2 sites, the ewes were mated in the autumn, first at 7 mo of age, and at 2 sites the ewes were mated in the spring, first at 14 or 17 mo 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 rate, fetal number, fertility (ewes lambing), litter size, lamb survival, number of lambs born (NLBj), number of lambs weaned (NLWj), and total weight of lamb weaned (TWWj) per ewe bred. Fixed effects included sire breed (1 to 10), environment (1 to 4, site and season of breeding: autumn, spring), breeding (1 to 3), cohort (1 to 3), and their interactions. The REML procedures were used to estimate (co)variance components. Ewe sire breed effects were significant (P < 0.01) for all the reproductive 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 breeding 1 vs. 2 and 3 was considerably greater than the contrast between breeding 2 vs. 3, with significant environment x breeding 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 a 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 reproductive traits.