Sand cracks
Heredity and nutrition are often implicated as causes of sand cracks, which make cows lame and can lead to premature culling of stock. But Jim Armstrong, livestock agrologist with Saskatchewan Agriculture in Tisdale, suspects there may also be a strong link with selenium toxicity.
“Selenium supplementation came to the front when research showed that a deficiency of selenium by itself or in conjunction with vitamin E could lead to white-muscle disease, which can result in the death of calves,” said Armstrong.
“Producer response was to supplement selenium, and soon every mineral, salt and protein supplement had a registration for added selenium.”
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Over the past 10 years, selenium levels in supplements have increased, and some producers treat every newborn calf with a shot of selenium-vitamin E. As a result, the incidence of white-muscle disease has decreased. But Armstrong wonders if the supplement programs are overdone. While many livestock feeds are deficient in selenium, he notes some may contain high levels.
For example, some wild plants, such as certain vetches, accumulate selenium. Heavy fertilizer rates can turn some plants into selenium accumulators. And there is evidence that some forages produced on sandy soils may contain higher levels of selenium than those produced on clays.
Armstrong said a sample of producers who have sand crack problems in their herds have the following similarities: the herds are fed high levels of minerals containing added selenium; many producers feed additional selenium close to calving time to prevent white-muscle disease; most feed minerals with added selenium on a free choice basis, plus some is added to a grain diet; and several believe the incidence of sand cracks increased after supplementation with selenium began several years ago.
Mineral consumption
A compounding factor may be animal behavior. Mineral consumption is very erratic. Cows can consume from none to eight ounces of mineral per day, he said.
But minerals react with other nutrients in the diet, said Armstrong. This complexity makes the definition of sand-crack problems difficult to pinpoint.
“Do we need to match mineral supplementation to specific farms and feed sources, rather than to a region? Are there situations where free-choice feeding can lead to toxicities? Could the name sand cracks, which was originally coined for a foot condition of cattle grazing sandy land, relate to excess selenium?” he asked.
Armstrong and Al Foster, a rangeland agrologist with the Grazing and Pasture Technology Program in Tisdale, are studying selenium intake in three problem herds in the area.
Forages will be tested, mineral consumption monitored, blood samples tested and winter forage analyzed.
The two are working with Paul Greenough of the College of Veterinary Medicine in Saskatoon. Greenough’s investigation into the link between sand cracks and the change from winter feed and lush pasture is continuing.
Producers interested in assisting in the research can call Armstrong at 306-878-8804.
– Saskatchewan Agriculture
