The U.S. sheep industry is built on a foundation of diverse breeds, each adapted to specific environmental conditions and management systems.
From fine wool to long wool, hair to dairy, and all in between, genetic diversity enables producers to select animals best suited for their production goals. However, balancing uniformity for consistent production with maintaining enough genetic variability for resilience and adaptability remains challenging.
The Sheep GEMS project—GEMS stands for Genetics, Environment, Management and Society—aims to address these challenges by incorporating genomic technologies into breeding programs, enhancing sustainability and improving genetic evaluation tools.
Sheep GEMS has been underway for about two years and has generated valuable insights into sheep genetics. Scientists at the Dale Bumpers Small Farms Research Center, the U.S. Meat Animal Research Center and the U.S. Sheep Experiment Station are collecting data on Katahdin, Polypay, Rambouillet and Suffolk breeds. The project has partnered with the National Sheep Improvement Program (NSIP) and recruited 45 NSIP flocks to gather similar data, ensuring that findings are applicable across production systems.
A key aspect of Sheep GEMS is understanding and defining critical traits that contribute to an animal’s overall performance of robustness and climatic resilience.
Sheep GEMS focuses on robustness traits such as lamb survival, udder health and resistance to gastrointestinal parasitism. Researchers evaluate lamb survival through birth weight, early postnatal survival and survival to weaning. Udder health is assessed by measuring udder depth and teat placement near lambing. For gastrointestinal parasitism, fecal egg counts and FAMACHA scores—anemia assessments—are recorded in lambs and ewes at critical times.
The project also examines climatic resilience, particularly ewe longevity, by tracking stayability—whether a ewe remains in the flock while staying productive. Additionally, researchers monitor body weights and condition scores at key physiological stages, such as breeding and weaning, to better understand how sheep adapt to changing environmental conditions.
Initial study
An initial study with Katahdin sheep demonstrated how genetics, environment and management interact. Researchers analyzed body weights, fecal egg counts and FAMACHA scores at around 90 days of age in over 3,500 Katahdin lambs from 17 flocks participating in NSIP. Fecal egg counts and FAMACHA scores provided insights into a lamb’s genetic ability to resist gastrointestinal nematode infections, particularly Haemonchus contortus, a common blood-feeding parasite in U.S. sheep and goats.
Researchers used 30 years of climate data to evaluate environmental influences, including rainfall, snowfall, temperature and elevation. Management practices were assessed through an online survey completed by 40 NSIP Katahdin producers, covering factors such as grazing systems, parasite control and feeding strategies.
Rather than considering environment and management separately, researchers combined them into nine “eco-management clusters,” which better captured differences among flocks. Flocks in hotter, wetter climates with pasture-born lambs exhibited higher parasite loads, while those turned out to pasture at older ages experienced less parasitism. Further analysis showed that specific sire families performed differently depending on the eco-management cluster in which their lambs were raised.
The interaction between sire genotype and cluster accounted for 12% of the variation in fecal egg counts and FAMACHA scores and 19% of the variation in body weights. Incorporating these interactions into breeding programs could improve selection decisions and accelerate genetic progress.
Sheep genetics
Sheep GEMS has provided an opportunity to capture genetic information from sheep across the U.S. to make genomic predictions of breeding values, verify parentage and identify genetic condition status.
To characterize the genetic diversity within the industry, Sheep GEMS has genotyped DNA from 15,586 sheep across four breeds in NSIP: Katahdin (12,495 sheep), Rambouillet (1,276 sheep), Polypay (1,292 sheep) and Suffolk (523 sheep).
Genetic research conducted through the Sheep GEMS project analyzed five key genetic conditions: ovine progressive pneumonia (OPP) susceptibility, scrapie susceptibility, double muscling (MSTN), callipyge (CLPG) and booroola fecundity (FecB).
The study found none of the four breeds—Katahdin, Polypay, Rambouillet and Suffolk—carried the CLPG or FecB mutations. The CLPG mutation, originally from the Dorset breed, has been largely removed from U.S. sheep populations due to its negative impact on loin muscle tenderness.
The FecB mutation, primarily used in intensive lambing systems, has seen little adoption in the U.S. The MSTN mutation, linked to improved muscle development, was found at low frequencies in Katahdins (4.3%) and Suffolk (6.2%) but was absent in Rambouillet and Polypay. This mutation particularly benefits terminal sire lines, where selection pressure could enhance its prevalence.
Notable differences in scrapie susceptibility were observed among breeds, with Polypay showing the highest level of scrapie resistance at 92%. Similarly, 93.3% of Katahdin, 92.5% of Suffolk and 83.5% of Rambouillet sheep were classified as either resistant or rarely susceptible. However, 15.8% of Rambouillet sheep were highly susceptible to scrapie, emphasizing the need for genetic selection to increase resistance. As part of the National Scrapie Eradication effort, ongoing research in the Sheep GEMS project will assess the potential unintended consequences of selecting for scrapie resistance, particularly concerning OPP susceptibility.
According to Ron Lewis, an emeritus professor at the University of Nebraska-Lincoln, the Sheep GEMS project will provide updates on udder health and parasite resistance in the coming months. — Charles Wallace, WLJ contributing editor
