376 Genetic Approaches to Improve Reproductive Performance in the U.S. Sheep Industry

Abstract

Abstract The U.S. sheep industry has experienced many changes over the last 50 years, the most prominent being a 75% reduction in the national breeding ewe inventory. Wool now accounts for ~10% of enterprise returns compared to ~80% from the sale of market lambs. Most breeding objective work indicates greatest emphasis should be placed on traits associated with ewe reproductive efficiency [e.g., number of lambs born/weaned (NLB/NLW), lamb survival]. Still, average NLB across the U.S. (1.07 lambs/ewe) and within geographic regions (East = 1.13, Midwest = 1.25, West = 1.09, Southwest = 0.79 lambs/ewe) remains low. Several genetic technologies are available to improve reproductive performance. Introgression of large effect gene variants, such as those within BMPR-1B, have increased NLB by ~1.0 and ~1.5 lambs in heterozygous and homozygous ewes, respectively. However, without joint improvement in maternal ability and/or husbandry, advantages in NLW are less pronounced and few U.S. producers utilize such variants in practice. Reproductive efficiency traits present challenges in selection programs as they are lowly heritable (< 0.15) and sex-limited. Previous single-trait selection experiments had modest improvement in NLB (0.01 – 0.02 lambs/yr). Selection accuracy is greatly improved by including pedigree and/or genomic relationships when deriving estimated breeding values (EBV). Since 2000, NLW EBV have increased by 0.01 lambs/yr with concurrent improvement in direct (0.02 kg/yr) and maternal (0.04 kg/yr) weaning weight for Polypay flocks enrolled in the National Sheep Improvement Program (NSIP). Still, NSIP flocks represent < 1% of production-oriented U.S. flocks so considerable expansion is needed to realize within-breed genetic improvement at a national level. Perhaps most importantly, large differences in reproductive efficiency traits exist across breeds and should be utilized to a greater extent in strategic crossbreeding systems. Optimizing reproductive performance for specific production environments is essential for the sustainability of the U.S. sheep industry.