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The Whens and Whys of Supplementing Iodine to Cattle
By: Raylene Nickel
Iodine deficiencies in beef cattle are rare. When they do occur, the broad-spectrum symptoms can be hard to pin down.
That’s because the trace mineral iodine plays a critical role in the maintenance of the thyroid, which regulates metabolism. Metabolism, of course, affects an array of physical processes.
“Signs of iodine deficiency include reduced fertility, enlarged thyroid (goiter), and stillborn, weak, and sometimes hairless calves,” says beef specialist Stephen Boyles, Ohio State University Extension.
Iodine-deficient soils can create the deficiency.
“Soils in the Great Lakes, Midwest, Northeast, and Rocky Mountain regions have been shown to be deficient in iodine levels. This results in crops and feedstuffs that are also low in iodine,” says Jeannine Schweihofer, Michigan State University Extension beef educator.
Testing forages may reveal whether or not these feeds are supplying livestock with sufficient iodine. The normal requirement for iodine in the diet of beef cattle is 0.5 parts per million (ppm) of the total diet.
“Including iodized salt in the base mineral mix should, in most cases, provide adequate iodine supplementation,” says Boyles. “Ethylenediamine dihydroiodide (EDDI)also provides a quality source of available iodine. The EDDI is often included in trace-mineral supplements as a foot rot preventative.”
When goitrogenic feeds are part of the ration, he recommends increasing the supplemented rate of iodine to 1 to 2 ppm of the total diet.
“Goitrogens are dietary components that inhibit iodine uptake from the gut,” says Schweihofer. “Feeds containing goitrogens are brassicas like turnips, rapeseed, or kale. Parts of other feeds (such as white clover, carrots, linseed, cassava, sweet potatoes, lima beans, millets, peanuts, cottonseed, soybeans, and sugar beet pulp) also have the ability to decrease iodine uptake.”
Risk in Cover Crops
Cattle grazing cover crops containing goitrogenic plants are potentially at risk for iodine deficiency. “For these cattle, iodine can be supplemented in the salt at a rate that is two to four times the normal requirement,” says Boyles.
“You can buy iodine sources such as EDDI and calcium iodate. These are the most stable,” he says. “Use a loose form of mineral rather than relying on a block if a known deficiency exists. You can also direct-feed it with grain and make sure that all cattle eat at the same time. Iodine toxicity has occurred when dietary levels exceed 200 to 400 ppm.”
To determine your herd’s needs and the actual rate of iodine to include in salt or mineral mixes, consult your veterinarian.
Supplementing with iodine becomes increasingly critical if certain diseases begin appearing in the herd.
“While we can’t say these conditions actually result from an iodine deficiency, we do see conditions in cattle that are susceptible to iodine supplementation and treatments,” says Gerald Stokka, North Dakota State University Extension veterinarian.
These conditions – or diseases – include foot rot, wooden tongue, lumpy jaw, and soft-tissue swellings about the neck and jawline.
Foot rot, for instance, is caused by bacteria that enter the soft tissue above the hoof or between the toes when a small injury or an abrasion creates an opening.
Likewise, lumpy jaw and soft-tissue swellings about the neck and jaw tend to appear when potentially lacerating forages, such as barley beards or thistles, are part of the diet.
Causes aside, these conditions seem to respond to iodine treatment and may occur less when supplements are included in the diet.