Sire Breed, Litter Size, and Environment Influence Genetic Potential for Lamb Growth When Using Sire Breeding Values.

Khama R Kelman,Graham E Gardner,David W Pethick,Clair Alston-Knox

doi:10.3390/ani12040501

Abstract

Simple SummaryPrevious studies have demonstrated a reduced response to sire growth breeding values when there is poor ewe nutrition, resulting in lighter lambs. The current study has demonstrated that production factors which influence lamb growth, such as birth type, rear type, or sire breed, have a similar effect. The reduced growth in lambs is quantified in this study to provide lamb producers with realistic expectations of lamb growth, when high growth sires are used in combination with production factors which influence growth.Lamb growth can be optimised with genetic selection using sire Australian sheep breeding values, however, breeding value expression has been shown to be reduced with poor nutrition. It was therefore hypothesised that the genetic potential for lamb growth would also be reduced, where production factors such as multiple births limit growth. Live weights at birth, weaning, and post-weaning were collected from more than 18,000 lambs produced over five years and eight locations of the Sheep Cooperative Research Centre Information Nucleus Flock experiment, and the impact of environment, production factors, and genotype was determined using mixed effects regression. The genetic potential for lamb growth was moderated by environment, multiple births, and sire type (p < 0.05). Twin lambs achieved 76% of the expected weight gain at weaning and 58% post-weaning. For triplet lambs weight gains were drastically less at approximately 30% of the expected gain at the same time points. Lambs born to maternal sires consistently had the poorest response to genetic selection, achieving approximately half the expected weight gain. Hence, producers need to temper expectations for growth based on genetic selection, or employ mitigation strategies such as precision feeding, the use of alternate breeds, or place emphasis on the genetic merit of other desirable traits.

Highlights

Weighing lambs at key time points in production is a common practice employed among sheep enterprises
Environmental factors, production factors and genotype all affected lamb weight (Table 3)
Lamb growth is influenced by on-farm production factors and genetic selection for growth using sire Australian sheep breeding values (ASBVs)

Summary

Introduction

Weighing lambs at key time points in production is a common practice employed among sheep enterprises. Lamb weights are known to be influenced by production factors such as multiple births, dam age, and the sex of the lamb, with ewe lambs, lambs from 1 year old dams, and multiple birth lambs tending to be lighter at birth [3]. Environmental factors such as the site and timing of birth have an effect, with lamb weight increasing by up to 10% between seasons for lambs born at the same site [3]. Producer expectations of lamb weight need to be tempered by environment and where the enterprise structure or breeding objectives favor specific genotypes or production factors that can influence lamb weight, such as increased litter size in prolific flocks

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