Polioencephalomacia (polio) is a disease that can become a problem in some sheep flocks, North Dakota State University Extension Service sheep specialist Reid Redden warns.
It is characterized by the death of brain cells and is different from human polio, according to Neil Dyer, director of NDSU's Veterinary Diagnostic Lab.
Rising feed costs have many livestock producers, including shepherds, looking for less-expensive alternatives to traditional feedstuffs. However, some of these changes may result in animal health problems such as polio if diets are not balanced adequately for vitamins and minerals.
The primary cause of polio in sheep is thiamine deficiency, or a disturbance in how the body uses thiamine. Thiamine (vitamin B1) is produced naturally in the rumen of sheep on a normal diet.
Feeding high-grain diets to ruminants can predispose them to polio because it slows thiamine production in the rumen and increases mechanisms that degrade thiamine produced in the rumen. Therefore, supplemental thiamine should be added to all high-grain sheep diets to prevent polio, Redden says.
Sheep suspected of having polio from a thiamine deficiency recover quickly after a few treatments with vitamin B-complex.
Another cause of polio in sheep is elevated levels of sulfur (greater than 0.43 percent dry-matter basis) in the diet or sulfates (greater than 3,000 parts per million) in the drinking water. A high level of sulfur leads to the production of hydrogen sulfide in the rumen. Hydrogen sulfide makes its way into the blood stream and eventually causes brain damage.
Some alternative feeds, especially distillers byproducts, can contain high levels of sulfur. Drought conditions can reduce the water quality of ponds and reservoirs that livestock use as their primary water source. The best method of preventing polio from excess sulfur is to test feed and water sources, Redden says.
Plants such as bracken fern and horse tail also contain enzymes that can cause polio. Additionally, amprolium, a drug used to treat coccidiosis, can cause polio if given at high enough doses. However, these causes of polio are much less common.
Sheep affected by polio typically are isolated from the flock and exhibit signs of blindness, Dyer says. If the problem progresses, they tend to arch their back with their head up and appear to be stargazing. Sheep often are found on their side, with their feet paddling, and are unable to get up. Depending on the weather conditions and severity of the disease, death typically occurs within hours to a few days.
Polio most often is seen in lambs from a few weeks to 6 months old; however, it can affect sheep of any age. Sheep producers who suspect polio in their flock should contact their attending veterinarian for treatment and prevention advice.