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

Abstract

ABSTRACT: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.

Genetic correlations between wool traits and carcass traits in Merino sheep

“…The estimates of variance components and heritability for the wool production and quality traits and visual scores were reported by Mortimer et al (2017) and are not repeated here. There were high heritability estimates for the major wool production and wool quality traits whereas other wool quality, wool color, and visual traits were more moderately heritable, which is consistent with the review of Safari et al (2005) and more recent reports from several large Merino data sets (Asadi Fozi et al, 2005;Safari et al, 2007;Huisman et al, 2008;Swan et al, 2008Brown et al, 2010Brown et al, , 2013.…”

Genetic correlations between wool traits and carcass traits in Merino sheep1

“…Additionally, adult BCOV was not scored on animals born in 2007, 2010, and 2011. Further details of the measurements, including the means and SD and the genetic variances for each of the yearling wool traits, are reported in the first paper in this series (Mortimer et al, 2017).…”

“…The number of records, mean, SD, and the number of sires and dams for each of the carcass measures and carcass dissection traits are shown in Table 1. Genetic and phenotypic correlations were also estimated between the carcass traits and ultrasound measures on live sheep at postweaning and yearling ages for fat depth (postweaning live ultrasound fat [C site; pwFATUS] and yearling live ultrasound fat [C site], respectively) and eye muscle depth (postweaning live ultrasound eye muscle depth [pwEMDUS] and yearling live ultrasound eye muscle depth, respectively; see Mortimer et al [2017] for details of the ultrasound traits).…”

“…Before estimating the variance components, mixed linear sire models initially were fitted to the wool traits and the carcass traits separately to identify significant environmental effects. The fixed effects included site (8 levels), year of birth (5 levels), sex (2 levels; wool traits only), sheep type (3 levels: ultra/super fine, fine fine/medium, and medium/strong), type of birth and rearing (6 levels: 11, 21, 22, 31, 32, and 33 for number of lambs born and reared, respectively, and dam age (7 levels: 2 to greater than or equal to 7 yr of age; see Mortimer et al [2017] for more details). For the carcass traits, slaughter group was also fitted as well as age of the lamb as a linear covariate.…”

“…This second paper of a series reports estimates of genetic and phenotypic correlations between several wool production and quality traits and carcass meat traits, including lean meat yield and the weight of various cuts, from Merino sheep in the Information Nucleus (IN; Fogarty et al, 2007;van der Werf et al, 2010). The first paper reported genetic parameters for production and quality traits for wool and meat measured in live animals (Mortimer et al, 2017). These genetic parameters will contribute to calculation of more accurate EBV and selection indexes for gains in dual-purpose breeding objectives.…”