Sheep Industry News August 2021

Figure 1

and loin muscle depths, fleece weight and quality measurements, and fecal egg count. Producers receive EBVs on these traits to augment their selection decisions. NSIP also provides producers with economic selection indices. Rarely does our breeding objective – our direction – involve fo cus on only one trait. Selection indices provide a single value that breeders can use to select several traits simultaneously that define overall profit. They are constructed by considering the eco nomic contribution of the various traits included in the breeding objective. In being a single value, these indices certainly make the selection process much easier. NSIP provides several indices tailored to individual breed types and production conditions. Still, what about fairly comparing animals raised in different flocks? That too is rectified through NSIP. By sharing primarily rams across flocks, those flocks become genetically connected (related). Through those connections – combined with the statistical tools we use in genetic evaluation – we can disentangle differences in performance due to genetics from those due to environment. Animals can be reliably compared across flocks, generating a much larger pool of sheep to select among. Selection intensity increases along with selection response. As an illustration, let us consider genetic gain in a maternal breed with a focus on number of lambs reared and dams’ (mater

nal) contribution to their offspring’s weaning weight. In Figure 1 (above), selection response is shown by plotting the average EBV against birth year in the past 10 years for these two traits. The gains have been substantial. The number of lambs reared have increased by 1.2 percent annually. The maternal weaning weight has increased by 0.11 pounds annually. Combined, they equate to more and heavier lambs weaned, with improved profitability. But can we do even better? The answer is yes, and that is where genomic technologies provide tremendous opportunity. THE WONDER OF GENOMICS Genomics is now routinely used in most livestock breeding programs in the United States and worldwide, and has made tremendous contributions toward increasing the rates of genetic progress in many populations. Based on a small tissue sample of an animal, a technology called a Single Nucleotide Poly morphism chip is used to read the DNA sequence of an animal at thousands of different sites distributed across the animal’s chromosomes. The DNA sequences at those sites are referred to as genetic markers and capture genetic differences in animals that impact their performance. Different SNP chips are commercially available, and they mainly differ in the number of genetic mark ers that are included.

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