Sheep Industry News August 2025

productive in the flock—most often measured as the number of days between her first and last lambing. Ewes that stay in the flock longer can help improve profitability by lowering the need for replacements, producing more lambs over their lifetime, and often have fewer health or reproduction problems. In our work with Katahdin sheep, we found that about one-third of ewes were removed from the flock before they had a second lamb crop. Even among ewes that lambed at least twice, half had a productive life of less than three years.” I quizzed Luiz on how we can best incorporate ewe longevity into breeding programs going forward. He replied, “based on records from NSIP producers, Katahdin ewes, on average, had their last lambs at around three years of age, producing about 2.7 litters over their lifetime. But these numbers differed among ewes, which is heritable, meaning we can improve ewe longevity through selection.” “We recommend that breeders keep track of why and when ewes are culled. This would help improve the way in which we evaluate ewe longevity. We found that the total number of lambs weaned by a ewe over her lifetime was the best measure to use. Selecting for this trait would help increase both ewe productivity and longevity. It also would make the flock more profitable and allow for stronger selection of replacement females.” The Sheep GEMS team is interested in interconnections among its four facets mentioned above. This leads us to consider a topic known as genotype by environment interaction or GxE. I asked Luiz to ex plain GxE and how it is evaluated. “GxE means that the way a sheep performs can depend on both its genetics and the environment it is raised in. In other words, a ram that sires fast-growing, healthy lambs in one type of environ ment, like a cool, grassy pasture, might not produce offspring that do as well in a hot, dry region with less forage. This concept is especially important in national programs like NSIP, which aim to compare and improve sheep across a wide range of farming and ranching conditions in the U.S. To study GxE, we look at perfor mance and genetic data from sheep raised in different settings to see if certain bloodlines do better in some environments than oth ers. Importantly, we have detected GxE in some key traits around weaning time, namely weight and fecal egg count.” When asked whether he could speculate on its impact on ranch or farm practices going forward, he responded, “As tools like genomic selection become more common in the sheep industry, understand ing GxE will help breeders and producers make better decisions. It could lead to breeding values or selection indexes that are customized to specific weather conditions or production systems. This means farmers and ranchers might eventually choose rams not just based on

general performance, but on how well their genetics fit local condi tions—whether that is heat, high humidity, arid conditions, or limited feed. In the long run, this approach can lead to more resilient and efficient flocks.” Dr Brad Freking, a Research Geneticist at U.S. Meat Animal Research Center (USMARC), contributes to Sheep GEMS by evaluat ing genomic data on the four breeds engaged in the project. At this point, 14,313 Katahdin, 2,414 Polypay, 2,055 Rambouillet, and 1,654 Suffolk genotypes have been accumulated. I asked Brad why collecting genotypes is so important, and why the choice of genotyping tool or platform used in the project, which evaluates 50,000 genetic markers, mattered. “In Sheep GEMS, the choice of this medium-density genotyping platform was because it currently provides the most cost-effective way to generate the genomic information that achieved three aims: to generate more accurately estimated breeding values from genomic prediction, which we call genomically enhanced EBV; to verify the recorded pedigree information; and to determine some economically important genetic conditions.” “Genomic prediction uses genetic markers to estimate genetic merit earlier in the life of the animal than just pedigree and phenotypic information alone. For example, two full sibs could be compared at birth and differentiated from each other at birth for carcass merit traits rather than waiting for the traits to be measured later. In addition to genomically enhanced EBV, pedigree errors can be identified and fixed if needed, and genetic status for multiple genetic conditions can be gathered from the same DNA sample.” Producers participating in Sheep GEMS are provided with infor mation on genetic conditions in their sheep, like ovine progressive pneumonia (OPP) and scrapie susceptibilities. Brad summarized what has been learned this way, “genetic condition status can be useful in selection or culling, and mating, decisions and in marketing programs. For two of the five validated genetic conditions—Booroola fecundity and Callipyge—we find very little or even no occurrence of the causal mutation in our U.S. breeds. Double muscling appears in some breeds to a small extent.” “The four breeds in Sheep GEMS, however, are at different end points in achieving the favored genetic status for low susceptibility to OPP and resistance to scrapie. The Polypay and Rambouillet breeds are already at a high frequency—over 85%—for the favorable forms of genetic markers for low susceptibility to OPP. However, in Katahdin and Suffolk, nearly 60% of the genotyped animals were genetically susceptible to this disease.”

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