Sheep GEMS News Brief 14 – May 2025
Previously, we introduced the concept of eco-management cluster—groups of flocks that share similar climate and management practices. These clusters are the foundation of our approach in Sheep GEMS for building genetic evaluations that more closely consider production environments. We are still exploring the makeup of eco-management clusters, as they undoubtedly differ among breeds. However, one of their important uses is in our study of genotype-by-environment interactions (G×E).
G×E occur when the ranking of animals based on their genetic potential changes depending on the production environment in which they are managed. As an example, consider weaning weights recorded on the offspring of two sires. In one eco-management cluster, the offsprings of the first sire weigh more than the second. However, in a different cluster, the offspring of the second sire weigh more than the first. The rankings changed and, so, we have G×E. If the weights of the offspring of both sires were consistently heavier in one eco-management cluster than in the other, clearly one production environment was more favorable for weight gain than the other. However, with no change in ranking, there would be no G×E.
Our genetic evaluations of sheep in the U.S. currently assume animals rank the same genetically across production environments. While this simplifies comparisons, it may not fully reflect what producers see in their own flocks. Ignoring G×E could limit the effectiveness of selection programs, especially in a country as diverse in both geography and management as the U.S. Recognizing and accounting for these interactions may allow us to identify animals that are well-suited to specific production systems. This is especially important for traits that are more influenced by environmental conditions, including growth rates, reproductive success, and disease resistance.
In an earlier study at the University of Nebraska–Lincoln, we found that G×E impacted the way animals performed. Using data from Katahdin sheep enrolled in the National Sheep Improvement Program, we compared the performance of the offspring of the same sires in different eco-management clusters. The differences were substantial. We explained about 19% of the variation in weaning weights by G×E. Furthermore, G×E accounted for about 12% of the variation in parasite resistance, which we measured using fecal egg counts and FAMACHA scores. The choice of the “best” sire in one production environment, therefore, may not be the best choice in another.
We are now testing for the presence of G×E in other breeds, namely Polypay, Rambouillet, Suffolk, and Targhee. Our first step is to determine if enough sires have been used in common across enough of the eco-management clusters. That is unlikely for some traits (those not normally recorded in all flocks), but we remain hopeful.
Considering G×E in genetic evaluations does add complexity but, very importantly, it also adds opportunity. It may help us match the right genetics to the right production environments, improving the bottom-line for U.S. sheep operations.
For further information contact Hilal Yazar Gunes (hyazargunes2@huskers.unl.edu).
Acknowledgements. We thank the producers participating in the National Sheep Improvement Program for completing an on-line survey of their management practices. The information on G×E in Katahdin sheep were from research conducted by Brian Arisman. This work was supported by the Organic Agriculture Research and Extension Initiative (grant 2016-51300-25723/project accession no. 1010329), and by the Agriculture and Food Research Initiative Competitive Grant (grant 2022-67015-36073/project accession no. 1027785), from the USDA National Institute of Food and Agriculture. The USDA is an equal opportunity provider and employer. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the USDA.
