white muscle disease (wmd)-stiff lamb disease-nutritional muscular dystrophy
What is it? White muscle disease is a degenerative muscle disease found in all large animals. It is caused by a deficiency of selenium and/or vitamin E. Generally, it is not known which. Certain areas of the U.S., including the Northeast, are considered low in selenium levels. Selenium deficiency occurs when the soil contains less than 0.5 mg Se/kg of soil and locally harvested feeds contain less than 0.1 mg Se/kg of feed.
Pasture, hay, grain, and other supplements can be analyzed to determine the amount of selenium to be added to supplemental feeds. Grazing sheep usually consume adequate amounts of vitamin E. Fresh legumes and pasture are good sources of vitamin E whereas silage, oil seeds, root crops, cereal grains, and dry hays tend to be poor sources of vitamin E. Prolonged storage of feedstuffs results in a degradation of Vitamin E content.
In addition to white muscle disease, selenium and vitamin E deficiencies can produce symptoms of ill thrift and reproductive losses. They can cause poor rate of growth or ill thrift in young lambs throughout the growing period. Selenium and vitamin E also play key roles in the animal’s normal immune response.
Symptoms. White muscle disease is most commonly found in newborns or fast growing animals. Kids are believed to be more susceptible than lambs, possibly because they have a higher requirement for selenium. The disease can affect both the skeletal and cardiac muscles. When the skeletal muscles are affected, symptoms vary from mild stiffness to obvious pain upon walking, to an inability to stand. Lambs/kids may tremble in pain when held in a standing position. Affected lambs/kids are usually bright and have normal appetites. When the problem occurs in newborns, they are born weak and unable to rise. When the disease affects the heart, the animal shows signs similar to pneumonia, including difficult breathing, a frothy nasal discharge (may be blood stained), and fever. The heart and respiratory rates are elevated and often irregular.
Treatment. Treating the heart form of white muscle disease is usually ineffective. The muscle form of the disease can be treated with supplemental selenium and/or vitamin E. Producers need to follow label directions carefully when using selenium for treatment. The concentrations of selenium (per ml) vary greatly with each product, and excessive or repeated injections can result in selenium toxicity and possibly death. The commercially available selenium/vitamin E product(s) commonly used in the U.S. do not contain therapeutic levels of vitamin E. Additional vitamin E may need to be provided through an injection of vitamin E alone or through oral vitamin E products.
Prevention. Deficiencies occur when animals are fed poor-quality hay or straw or lack access to pasture. Selenium deficiency can be confirmed by measuring selenium levels in whole blood or tissues. A diseased animal will have less than 0.04 ppm of selenium in its blood. Breeding ewes require more selenium, and their blood levels should be over 0.5 ppm.
White muscle disease can be prevented by supplementing the diet of susceptible animals with selenium and vitamin E. Since it occurs mostly in lambs and kids whose mothers were fed a selenium-deficient diet, supplementation of pregnant animals helps reduce disease in newborns. This is because selenium is transferred from dam to fetus across the placenta and also is present in the colostrum. While Vitamin E is not transmitted across the placenta, colostral levels of Vitamin E increase with ewe supplementation.
Selenium supplementation is controlled by law. For sheep, selenium can be supplemented in a complete ration at a level up to 0.3 ppm, in a feed supplement so that the intake of selenium does not exceed 0.7 mg per head per day, and in salt/mineral mixes at 90 ppm as long as total daily consumption does not exceed 0.7 mg/head/day. Selenium supplementation of feed has not been approved specifically for goats.
Injectable selenium compounds are available to prevent WMD in at risk-animals; however, injections are a poor alternative compared to routinely providing adequate selenium and vitamin E in the diet. Ideally, the total diet for sheep and/or goats should contain 0.10 to 0.30 ppm of selenium.
References: Sheep & Goat Medicine edited by D.G. Pugh (2002) and Sheep Production Handbook by American Sheep Industry Association (2002).
Reprinted with permission by Susan Schoenian
Editor, Maryland Sheep and Goat Producers
from the February 2004 issue.
Copyright 2004 BBSAI. All rights reserved.