ASI podcast examines risk factors for white muscle disease in sheep
During an April 27 episode of the American Sheep Industry Association (ASI) Research Update Podcast, University of Wyoming Extension Sheep Specialist Dr. Whit Stewart discusses risk factors for white muscle disease in lambs, as well as the importance of proactive nutrition to help combat the issue.
Hosted by Jake Thorne, Texas A&M AgriLife Extension sheep and goat program specialist, the episode delves into an issue which can quietly rob producers of lamb vigor, growth and survivability – selenium deficiency.
“From weak newborn lambs to cases of white muscle disease, getting trace mineral nutrition right can have a major impact on flock performance and the bottom line,” Thorne emphasizes.
Stewart’s comments focus on how to identify and combat risk factors for selenium deficiency leading to white muscle disease and emphasize the importance of proactive nutritional management practices to help producers ensure lamb health.
White muscle disease
To kick off the conversation, Stewart provides a scientific explanation of white muscle disease and its relationship to selenium deficiency.
White muscle disease, or nutritional myopathy, is a degenerative condition of skeletal and cardiac muscle caused by failure of the antioxidant system, Stewart explains.
The most common causes of white muscle disease are selenium deficiency and vitamin E deficiency, as both nutrients play a vital role in regulating internal functions.
In cases of white muscle disease, oxidative damage causes muscle cells to break down resulting in tissue death and a whiteish appearance to the muscle.
In skeletal cases, Stewart says general weakness, stiff gaits and difficulty standing are all warning signs of the disease, while cardiac cases often result in sudden death, paralysis and respiratory distress.
“The hallmark is loss of function, not structural abnormality,” Stewart emphasizes. “If the system falls behind, you start to see these problems.”
Importance of selenium
Selenium plays a vital role in several key bodily functions. In sheep, Stewart explains higher levels of selenium have been linked to better performance under heat stress conditions, as well as improved reproduction.
The mineral is also critically important to regulating thyroid function, as well as neutralizing oxidative stress and promoting muscle health.
For these reasons, ensuring adequate selenium intake is vital to ensuring flock performance in ewes, lambs and rams alike.
Ensuring adequate intake
Stewart notes promoting sufficient selenium levels in lambs starts with implementing proper nutritional strategies in ewes, emphasizing the process of passive transfer helps equip lambs with essential nutrients including selenium.
“A lot of minerals are deposited across the placenta, especially as the fetus is developing,” Stewart says. “Requirements increase dramatically from breeding to gestation and into lactation.”
“Ewes are not only producing a lot of energy to produce milk, but they’re also shuttling minerals,” he adds. “Oftentimes we forget – especially with selenium – a good mineral program and ensuring good intake during gestation is a way to fortify lambs growing inside ewes with an adequate mineral status.”
Further, he notes there are injectable solutions which can help treat true cases of selenium deficiency in lambs but strongly recommends producers focus on proper nutrition as a preventative measure first and take the proper diagnostic steps to identify white muscle disease before administering injectables indiscriminately.
Regarding whole flock health, Stewart says having a good vitamin and mineral package to supplement alternative feed sources in areas of drought and on ranges with poor-quality forage is vital.
Testing protocols
Stewart explains there are several testing options producers can implement to monitor selenium levels in soils and feedstuffs, including supplements, and recommends producers do so to better understand intake levels.
He also warns producers to be wary of selenium toxicity and take extra precautions to ensure supplements do not exceed the recommended limit and not to feed excess supplements in areas of selenium-rich forage.
On the topic of ranges, Stewart recommends testing soils across all potential grazing sites and testing any outside feed sources – particularly hay fed during lambing – for selenium levels.
In cases of death loss where producers are concerned about white muscle disease, Stewart recommends testing tissue samples to analyze nutrient deficiencies and comparing the results to evaluate management practices.
“Testing biological tissue will tell you with a high degree of certainty whether your management protocol was adequate or not,” Stewart says, adding local Extension resources and state diagnostic labs provide reference ranges to help interpret findings.
Overall takeaways
In closing, Stewart offers some overall takeaways, once again emphasizing ensuring adequate selenium intake starts with providing proper nutrition.
Further, he reiterates passive transfer from colostrum equips newborn lambs with vitamins and minerals in addition to antibodies and recommends paying close attention to ewe nutrition and management to ensure a healthy lamb crop.
“Get a good program in place at breeding to ensure these animals get off to a better start,” Stewart says. “Prioritize management when it pays off the most.”
Grace Skavdahl is the editor of the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.
