Sheep Industry News August 2025

Where Performance Meets Progress: Lessons from the Wyoming Ram Test

Dylan Laverell, (University of Wyoming Extension Sheep Program) Tom Murphy, (USDA – Agricultural Research Service) Whit Stewart, (University of Wyoming Extension Sheep Specialist) T he Wyoming Central Ram Performance Test was started in 1961 as a partnership between the University of Wyoming Extension, Agricultural Experiment Sta tions, and the Wyoming Wool Growers Association. For over six decades, it has evaluated ram lambs from a variety of West ern white-faced breeds through a 140-day testing period during which growth and wool quality traits are measured. From 2022 to 2025 alone, the Wyoming Ram Test evaluated over 360 rams from four breed types enrolled by 40 consigners representing six U.S. states and Canada. Central performance tests were once the mainstay of genetic evaluation and were located throughout the country. Their concept is to evaluate ram lambs that were born and reared on different sheep operations at a single location, thereby remov ing some of the non-genetic variation that can influence post weaning performance. However, central performance tests have important limitations. We now understand that the phenotypes measured during a ram test are shaped well before animals enter the facility. Factors such as birth and rearing type, dam age and milk production, pathogen exposure history, and many others can influence an animal’s phenotype even into adult hood but are challenging to account for in a traditional central performance test. Furthermore, some of the most economically important traits—like prolificacy, mothering ability, and longevity—are inherently excluded from evaluation in a male-only, post-wean ing centralized test. Perhaps most importantly, central perfor mance tests only consider an individual ram’s performance as a proxy for genetic merit and the performance of their genetic relatives is overlooked. In contrast, across-flock genetic evalu ations, like those used by the National Sheep Improvement Program (NSIP), correct for non-genetic effects and combine information from all available genetic relatives to generate trait estimated breeding values (EBV). Therefore, NSIP EBV serve as more accurate predictors of genetic merit than central perfor mance ram tests. Despite their inherent constraints, central performance tests provide a critical and consistent tool for making improvement in traits that can be objectively and reliably evaluated under controlled conditions. For those involved, data generated from the Wyoming Ram Test and others has served as a benchmark, enabling phenotypic trends over time to be estimated while providing key insights into underlying biological mechanisms

and husbandry associated with animal performance and health. Therefore, the Wyoming Ram Test continues to play a vital role in advancing the performance of fine-wool sheep across North America. Shifts in Productivity and Phenotype Data collected from central performance ram tests can be used to observe long-term phenotypic trends in ram growth and fleece characteristics. From 1949 to 1976, average daily gains (ADG) of rams in the Texas central performance test improved by nearly 50%, increasing from 0.31 to 0.72 lbs/day. Similarly, ADG of rams in the Wyoming test increased from 0.51 to 0.86 lbs/day from 1961 to 2013. During the last five years (2021 – 2025), rams on the Wyoming test averaged an impressive 0.97 lbs/day. Selecting for increased post-weaning ADG is associated with increased mature weight. Unsurprisingly, ram body weight at the end of the Wyoming ram test has also increased 21% (195 lbs to 235 lbs) from 1961 to 2011. Depending on your environment and availability of shearers, maximizing ADG may not be advantageous. While ADG and mature weight have increased, breeders have also made reductions in unfavorable traits such as wool blindness and skin folds (Figure 1) . Furthermore, fiber diameter on both

Figure 1. King Bros. Rambouillet rams used in a sheep short course at the University of Wyoming in 1904. From the Collections of American Heritage Center, University of Wyoming.

Rambouillet ram from the 2022 Wyoming Test, showing improvements in wool blindness, skin folds, and body size during the 118-year period.

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