99 Heritability and Repeatability of Structural Foot and Leg Traits in Sheep

Abstract

Abstract Similar to other livestock species, sheep are subject to a range of structural faults that contribute to lameness and involuntary culling. Record-keeping in the sheep industry is generally sparse, particularly for structural traits; thus, the extent of the problem is ill-defined. Furthermore, the few studies centered on foot and leg structure have typically involved small numbers of animals measured only once. Consequently, estimates of heritability for pasterns, and for claw and hoof conformation scores in sheep are sparse in the literature, with little consideration of potential score changes across an animal’s lifetime. Using a large dataset of repeatedly-measured scores, our objective was to reliably estimate the heritability and repeatability of several foot and leg traits indicative of structural soundness. Pedigree and performance data on 28,300 commercial crossbreed ewes were supplied by Focus Genetics, Ltd., New Zealand. The subjective foot and leg scores were recorded multiple times from first lambing to culling, with as many as 5 sets of records collected on individual ewes. The conformation traits evaluated were overall foot and leg conformation, rear pastern angles, front pastern angles, rear claw and hoof shapes, and front claw and hoof shapes. We fitted a repeatability model with fixed effects of recording age, age of dam, birth rank, rearing rank, heterosis (as a covariate), and contemporary group defined as the combination of birth year, birth flock, and recording mob. Random effects were direct additive, permanent environment, and residual. Heritability estimates ranged between 0.05 ± 0.01 for front claw and hoof shape score to 0.18 ± 0.01 for front pastern angle score. The corresponding repeatability estimates ranged from 0.13 ± 0.01 to 0.30 ± 0.01. The heritabilities estimated in our study were very similar to those obtained by Sheep Improvement Ltd., New Zealand; their estimates varied from 0.06 to 0.20 for the same traits. Based on the low heritability and moderate repeatability for these traits, culling animals based on their first recorded structural foot and leg scores may be risky. However, through their incorporation into a designed breeding program, genetic selection offers a viable approach to improve structural soundness in sheep.