Sheep Industry News August 2025

“It is important to establish a baseline level of genetic diversity prior to the implementation of genomic selection so we can assess the impact, if any, that genomic selection has on the overall genetic diversity of each breed. In the extreme case with dairy cattle, where few elite sires have been heavily used, genomic selection has led to an increased annual rate of inbreeding with negative impacts on fitness traits. While this is unlikely in sheep due to the limited use of A.I., it is still important to monitor and understand the impacts of genomic selection on inbreeding levels over time.” Evaluating lamb survival is another aspect being studied, and Car rie is taking the lead. when asked, “why do you consider lamb survival as key to improving the robustness of our flocks?”, she replied, “Any lamb that is born that does not make it to its end goal, whether that is a market lamb or to be retained as a breeder, is affect ing profitability. This trait has been reported in the literature for over 75 years, yet we have not been successful as an industry in improving this all-important trait.” “In our flock at the USSES, we evaluated 40 years of lamb survival data and made several conclusions. First, lamb survival is a different trait for a single, twin, or triplet. Second, a lamb’s survival is depen dent on the sex composition within its litter, particularly for triplet litters. Third, uniform birth weights within a litter support lamb survival. Lastly, young and old ewes have lower lamb survival and may need closer monitoring to ensure the survival of their lambs. Heritability estimates for lamb survival are extremely low, so I have been evaluating novel models to try to improve genetic selection for this trait. While the initial models still show low heritability for the trait, evaluation of lamb survival for singles, twins, and triplets as separate traits is showing some promise. Once we work through this in our flock, I look forward to seeing what we can do to improve selection for lamb survival across all NSIP flocks.” Earlier, I mentioned the producer survey conducted to gain insights into producers’ management practices. We are combining what we learned about management practices with weather condi tions specific to the location of individual flocks to define their overall production environments. These are called “eco-management clus ters”, and we use them as a ‘better’ definition of environment in our investigations of GxE. She then described the approaches taken to help better understand ways to improve lamb survival.

With his interest in udder health, I asked him why udder health is so important.

“In previous sheep industry surveys conducted by the USDA APHIS, he replied, it has been estimated that 14% of the U.S. breeding ewe flock is culled each year and, of these ewes, 15% are culled for ud der health issues such as hard bag syndrome and mastitis. While most of us are familiar with clinical mastitis like palpable lumps, abnormal milk, and so on, subclinical mastitis has major economic implications but goes unnoticed in most flocks.” In follow up, I inquired about what his evaluations of udder health entailed, and what has been learned from them. Tom replied, “To date, we have collected milk samples from over 2,500 ewes of varying ages, breed types, and production systems in our research flocks. These studies have found that approximately 25% of sampled ewes were visually healthy but had milk somatic cell count values indicative of subclinical mastitis. Furthermore, these sub-clinically infected ewes weaned, on average, 13 to 35 lb. less total weight of lamb than healthy ewes, which presents a substantial loss in potential revenue.” “The problem is that milking ewes to diagnose subclinical mastitis is extremely labor intensive and, while increased ewe milk produc tion generally results in heavier lamb weaning weights, heavy milking ewes are typically more prone to udder health issues. To improve ud der health in industry flocks we need to identify traits that are both easier to measure and indicative of udder health while balancing our selection efforts for optimal, rather than maximal, outputs. In many ways, this is easier said than done. However, our preliminary work in Sheep GEMS has found that udder depth and teat placement, both recorded on subjective scales of 1 to 9, are moderately heritable traits (20 to 35%) and most mature ewes have intermediate scores. These early findings are encouraging as we continue to evaluate selec tion strategies to breed more productive and longer-lived ewes.” The newest member of the GEMS team is Dr Carrie Wilson, a Re search Geneticist at the USDA, ARS, U.S. Sheep Experiment Station (USSES), she is assessing inbreeding in our sheep, a topic of particular interest to her and to sheep producers. I asked Carrie to explain what the team is doing on this topic, and why it is important to evaluate inbreeding levels in our breeds now. “We have used the full NSIP pedigree to compute inbreeding coef ficients for every animal for each breed participating in Sheep GEMS. This allows us to track trends over time and get an understanding of the inbreeding levels and rate of inbreeding for each breed. For animals that have been genotyped, we are able to measure genomic based inbreeding and get an even better understanding of the realized inbreeding in the breed.”

The team was also asked about their thoughts on the next steps af ter Sheep GEMS ends. The consensus was that, with the help of NSIP,

See Sheep Gems story on Page 35

August 2025 • Sheep Industry News • 31