One of the more widespread and noticeable effects of mineral deficiencies in cattle and sheep is white muscle disease.
White muscle disease (WMD) is most often caused by selenium deficiency. WMD is so named because the muscles of affected animals have literal white streaks, particularly in the heart.
“The heart muscle is one that, as you damage it, the damaged tissue gets replaced with fibrous connective tissue—scar tissue—and scar tissue in muscle is white,” explained Dr. Jeff Hall of Utah State University at the Cattlemen’s College during the recent National Cattlemen’s Beef Association annual conference.
“WMD is a common, serious, but preventable disease of young livestock, causing poor performance and death,” summarized Dr. Susan Kerr, DVM, and Washington State University Extension Director, in an Extension factsheet on the disease.
WMD was first discovered in the 1950s by Oregon State University’s Dr. James Oldfield. WMD is the common term for nutritional myodegeneration. It has been found in numerous species including all standard livestock species, horses, wild ungulates, poultry, and waterfowl. The effects are most noticeable in young livestock.
“Signs of [selenium] deficiency include muscle stiffness and tremors, motor disturbances, hind-end paralysis, and heart failure,” wrote a trio of Oregon State University (OSU) Extension researchers: Fara Brummer; Gene Pirelli; and Jean Hall. “These signs are most commonly observed in animals from 3 to 8 weeks of age.”
“Young animals may appear stiff, lame or weak; spend most of their time lying down and resting their chin on the ground; have diarrhea; and be unthrifty, chronic poor do-ers,” added Kerr.
The motor problems related to WMD stem from the fact the muscles are damaged. The tongue, heart, diaphragm, and major muscles in the hind legs are key sites of the white lesions. Excessive damage to the diaphragm and heart can lead to labored breathing and heart failure.
When it came to calves, Hall told attendees of the Cattlemen’s College that WMD can be observed in the tongue well before it is seen anywhere else.
“In a young calf, the muscle that has the highest metabolic activity is the tongue because of nursing,” he explained. “So, these calves will waste, not only because not only are they having trouble from not being able to nurse—so they have a nutritional deficiency—but at the same time they have the other difficulties associated with selenium deficiency.”
Sources of selenium
How much selenium an animal is getting boils down to selenium content of the feed and supplementation. The selenium content of livestock feed is largely dependent on soil conditions.
Some areas of the country have soil with adequate selenium levels. These are generally found in the Central Plains (both northern and southern). Other areas in the country have variable or low levels, particularly the Pacific Northwest, New England, and the South, according to the National Academy of Sciences.
Aside from soil, different plants take up selenium at different rates. Soil pH can also alter how available soil selenium is to plants.
“Soil pH influences the bioavailability of [selenium] in plants, meaning the degree to which plants can take [selenium] up in a form that animals can effectively utilize,” noted the OSU Extension researchers. “Acidic soil (lower pH) decreases plant uptake of [selenium], whereas alkaline conditions (higher pH) increase [selenium] uptake. Other minerals in the soil, such as sulfur, also may lower [selenium] bioavailability in growing plants.”
There are also different types of selenium; organic and inorganic. Organic selenium is usually the type found in forages, whereas most supplements are inorganic selenium. Organic selenium usually last longer in livestock’s systems than inorganic selenium.
“Selenium is the only micronutrient regulated as a feed additive by the Food and Drug Administration because of its potential toxic effects,” the OSU Extension researchers pointed out. There are some areas in the U.S. where naturally-occurring selenium toxicity can happen. As mentioned, different plants take up selenium at different rates.
“Eating [selenium]-accumulator plants can also poison animals,” cautioned the OSU Extension researchers. “These plants, which include species of Astragalus, Brassica, and Stanleya, survive in soils high in [selenium]. Although livestock do not typically eat these plants, care should be taken when pasturing animals in areas where they grow.” — WLJ
