Researchers analyzed more than 70,000 pedigrees and up to 48,000 performance records per trait.
National breeding records
A USDA Agricultural Research Service team examined US Suffolk sheep enrolled in the National Sheep Improvement Program. The analysis used a pedigree of 70,271 animals and up to 48,000 records per measured trait from more than 100 flocks. The Journal of Animal Science published the paper on 8 May 2026.
Different trends by trait
The analysis found steady genetic improvement in body weight and muscling. Reproductive traits showed lower heritability, and the authors reported signs of declining mothering ability. Traits studied included birth and post-weaning weights, muscle and fat depth, and the numbers of lambs born and weaned.