There has been increasing interest from commercial sheep producers to shift to shedding breeds such as the Dorper and Wiltshire Horn, which has triggered the development of shedding composite lines. This study analysed the genetic expression of spring shedding in adult ewes using a singlestep animal model, from which potential marker effects could be identified. Early investigations into the genetic architecture of shedding support previous literature which suggests that the trait is highly heritable and controlled by a dominant gene effect. However, further research of major SNP effects within this population and the multi-breed population within the Sheep Genetics LAMBPLAN is required.

Myostatin mutations have been identified in many beef breeds and have been associated with increased carcase yields, reduced fat, increased calving difficulty, delayed puberty and reduced female fertility. This study aimed to estimate the allele frequencies of myostatin mutations in Australian tropically adapted beef breeds. Nine myostatin variants (viz. C313Y, D182N, E226X, E291X, F94L, NT419, NT821, Q204X and S105C) were assessed in Brahman (n=2,554), Droughtmaster (n=2,188), and Santa Gertrudis (n=904) cattle that were part of the Repronomics research project. Results showed the myostatin variants NT821 and F94L were segregating in the Droughtmaster and Santa Gertrudis breeds but not in the Brahman. In total, 17.4% and 26% of Droughtmaster and Santa Gertrudis animals carried at least one copy of a myostatin allele for either variant. The frequency of the NT821 allele was 0.08 and 0.12, and the F94L allele was 0.01 and 0.02, respectively, for Droughtmaster and Santa Gertrudis animals. Hardy-Weinberg equilibrium was observed for both NT821 and F94L in both breeds. However, there were fewer than expected two copy NT821 animals for both breeds. With no variants detected in Brahman, the myostatin variants likely originated from the Bos Taurus influence of the Droughtmaster and Santa Gertrudis breeds. The allele frequencies of NT821 in the Droughtmaster and Santa Gertrudis breeds, along with the literature reports of increased calving difficulties associated with NT821, indicate that breeders should monitor and manage the presence of the NT821 myostatin variant. Further research should be undertaken to quantify the size of the effect that having one and two copies of the mutation has across all economically important traits.

This paper reports updated genetic parameter estimates for correlations between consumer eating quality and carcase traits for Australian sheep. Seven consumer sensory-assessment traits (tenderness, flavour, juiciness, smell, overall liking, star rating and MQ4 index) were collected on loin and topside cuts (n ~ 6,500). Heritability estimates (ℎ²) were low to moderate for these traits (0.09 < ℎ² < 0.26), with the topside cut having slightly more genetic variation than the loin. Genetic correlations (𝑟̂ _g) between sensory traits were high within cuts (𝑟̂ _g > 0.96) and across cuts (𝑟̂ _g > 0.73). There were moderate to high genetic correlations between the consumer sensory and the objective eating quality traits (intramuscular fat and shear force), and low to weakly negative correlations between the sensory traits and carcase lean meat yield. These estimates will be used to revise selection indexes and develop breeding values for consumer eating quality.

Computer image analysis is increasingly important in carcase evaluations to determine pricing in beef markets. Images captured by cameras can accurately predict carcase traits such as marble score and eye muscle area. As technology develops, older camera models are being replaced as newer versions are developed. This study estimated genetic parameters for carcase traits using the MIJ-30 camera and compared it to estimates based on the older Mirror-type camera. Traits investigated were hot standard carcase weight, AUS-MEAT marble score, HK-333 Japanese mirrortype camera fineness index and MIJ-30 fineness index. Univariate animal models were used to estimate variance components and heritabilities. Bivariate analysis was done to make pairwise comparisons between traits and estimate correlations. Traits were moderately heritable (0.33 – 0.58). The genetic correlation between the fineness index of the two cameras was 0.55 ± 0.19, indicating that measures from each camera should be treated as separate traits for genetic evaluation. This work supports the need to continuously validate newer carcase evaluation technologies to better understand evolving traits and how to incorporate them into genetic evaluations.