Building a better ewe: Lifetime productivity of Polypay sheep at the U.S. Sheep Experiment Station

Authors: Wilson, Carrie; Taylor, Joshua

Submitted to: Frontiers in Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/24/2026
Publication Date: 7/13/2026
Citation: Wilson, C.S., Taylor, J.B., 2026. Building a better ewe: Lifetime productivity of Polypay sheep at the U.S. Sheep Experiment Station. Frontiers in Animal Science. 7. https://doi.org/10.3389/fanim.2026.1868093.
DOI: https://doi.org/10.3389/fanim.2026.1868093

Interpretive Summary: Profitability of a sheep operation is influenced by the ability to maintain productive ewes in the flock beyond what is required to cover annual ewe costs. We were interested in evaluating the lifetime productivity of Polypay ewes who first lambed as 1-year-olds compared to 2-year-olds. Since ewe lambs are still growing, the general aim at the U.S. Sheep Experiment Station is for a ewe to lamb as a 1-year-old, but to have a single lamb to balance the needs of the ewe with the needs of her lamb. Consequently, we wanted to know if the ewe's first litter size had an impact on her lifetime productivity. Our findings were that ewes who lamb as 1-year-olds and who are prolific at their first lambing have a lifetime production advantage in this flock.

Technical Abstract: Ewe longevity is a primary concern for sheep producers since keeping productive ewes in the flock for as long as possible will help defray her development and carrying costs. Records from the U.S. Sheep Experiment Station Polypay flock from ewes born 1995 to 2016 were used in this evaluation and included 10,094 records from 2,941 ewes that either lambed as a 1-year-old (n = 2,399) or 2-year-old (n = 542) for the first time. The objectives of this study were to 1) compare lifetime productivity traits for ewes that lambed first as 1-year-olds to those that lambed first as 2-year-olds; 2) to evaluate the lifetime productivity of ewes based on the litter size at their first lambing; 3) to evaluate the influence of ewe body weight and ewe body weight change on lifetime productivity; and 4) to determine the cumulative genetic contribution of ewes that remained in the flock for at least 7 years compared to those that did not. The influence of age at first lambing (AFL) and prolificacy at first lambing (AFL_NLB) on lifetime productivity were of primary interest due to concerns that high prolificacy of a still-growing yearling could be detrimental in the long-term and thereby shorten her productive life. Stayability (STAY i|j) and marginal stayability (MARG i|j) were defined as the probability of a ewe to survive in the flock until i years old, given that she already survived until j years old. Ewes remained in the flock from 1 to 8 years, with an average of 3.02 ± 1.75 years, and an average annual replacement rate of 30.9 ± 9.7 %. Ewes who lambed as a 1-year-old had significantly higher lifetime lambs born (LLB), lifetime lambs weaned (LLW), and lifetime kilograms weaned at 120 days (LKg120d) than ewes who first lambed as 2-year-olds, but a significantly lower maternal rearing ability (MRA; LLW/LLB). Within the AFL_NLB categories, the highest LLB were observed by ewes who lambed as 1-year-olds with twins (1_2), 1-year-olds with multiples (1_3), and 2-year-olds with multiples (2_3) with the lowest LLB from ewes who lambed as 2-year-olds with a single (2_1). The highest LLW and LKg120d were from 1_2 and 1_3 ewes. Ewes who lambed as 1-year-olds had significantly higher STAY7|2, indicating greater longevity of the early prolific ewes. Ewe body weight did not differ at the various time points (mid-lactation, weaning, post-breeding, and mid-gestation) depending on STAY7|2 status. Changes in body weight were significantly higher from mid-lactation to weaning and from post-breeding to mid-gestation for the ewes that were present for STAY7|2. When evaluating the genetic contribution to the current generation, ewes that were present for STAY7|2 had a higher genetic contribution, a higher percentage of contributing ewes, and a higher percentage of highly influential ewes than ewes who were absent for STAY7|2.