Sheep Industry News May 2022

Suffolks in the pasture. Photo by Matt Beals, Dry Sandy Sheep Company. Opposite page: Suffolks were used in a recent ASI-funded project by the Leading Edge group in Utah. Photo by United Suffolk Sheep Association.

interval was 2.4 years for rams and 3.4 years for ewes. Inbreed ing – a measure of animal relatedness – averaged 5.5 percent. Although inbreeding has accumulated in Suffolk sheep, the annual rate of inbreeding has not increased. In some livestock breeds, only a few animals have substantially contributed to the current gene pool. Such was not the case with Suffolks. Only 14 animals contributed more than 1 percent to the current gene pool, with the most influential contributing 5 percent. This lack of highly influential individuals has helped maintain genetic diversity in the breed. The genotyping platform used in this study measured an ani mal’s genetic makeup – its DNA – at more than 600,000 locations along its chromosomes. Of the 64,000 pedigreed animals that were evaluated, a cross section of 244 individual animals were genotyped from flocks enrolled in NSIP. In addition, genotypes were collected on 60 rams from the USDA/ARS National Animal Germplasm Program gene bank. Those rams did not have NSIP associated pedigree records. In total, 304 sheep representing 32 flocks were genotyped. Those genotypes were then used to define diversity at the genomic level. Effective population size is defined as the number of individuals in a population who contribute offspring to the next generation. It, therefore, is important in understanding the genetic diver sity available within a breed. An effective population size of 50 is considered acceptable. Importantly, this number can be used to predict the accuracy that can be anticipated when obtaining GEBV. The effective population size for Suffolk was computed as 79.5, which is on the low side for sheep breeds. Still, the good news is a lower effective population size trans

lates into higher accuracies for GEBV, and higher accuracies gives us more confidence in our selection decisions. We also looked at change in effective population size over time; it has decreased substantially. Such a decline is typical, though, of livestock breeds that have undergone years of selection. Another measure of genetic diversity within a breed is expected heterozygosity, also called gene diversity. High heterozygosity means there is a lot of genetic variation. Since genetic variation is a key contributor to genetic change, we are interested in its value. For Suffolks, expected heterozygosity was computed as 0.317. This value indicates a high level of genetic diversity and is similar to that observed in other sheep breeds. Using both pedigree and genomic information, we also identi fied genetic differences among Suffolk flocks, which likely reflects differences in breeding priorities among producers. A baseline of genetic diversity has been established in U.S. Suf folk sheep. Our key findings were: • Inbreeding is low but accumulating; its rate is not increasing. • Genetic diversity in the breed is not limited by a few highly influential animals. • Effective population size is above an acceptable number and can be used to compute the anticipated accuracy of GEBV. • Expected heterozygosity is high, suggesting considerable genetic variation is still available for selection. Currently, only 12.5 percent of registered Suffolk sheep are included in NSIP. To achieve the ambitions of the ALB Industry Roadmap, additional participation is needed. As the Suffolk breed works toward the development of GEBV, now is the perfect time to join NSIP and move the American sheep industry forward.

May 2022 • Sheep Industry News • 15