"Water Hole" (c) 2009 arbyreed via Flickr Creative Commons
A report from the Colorado State University branch Vet Diagnostic Lab in the west-central region of that state reminds producers that the longterm effects of the Western drought continue to linger in health impact—in this case in the form of the brain-wasting disease polioencephalomalacia. Incidence of the disease related to high dietary sulfur levels, concentrated and compounded by the drought, have become more common in labs throughout the west, writes CSU’s Don Kitchen, head of the University’s Western Slope Lab. The alkaline soils common in Western Colorado and Eastern Utah have made the disease more likely during drought years.
In the case Colorado’s Kitchen describes here, about a thousand head of bred Angus calves were pastured on sub-irrigated land in a mountain river valley along the state line in eastern Utah. The large pasture contained two water sources: one, a spring fed pond; the second, a tank created by digging into the sub-irrigated ground and allowing the hole to fill with groundwater. Over about a weeks’ time, six animals either died or became recumbent. Necropsy findings in an affected 800-pound bred heifer showed the characteristic microscopic damage to brain cells, helping rule out other causes the condition can mimic, including Histophilus somnus, rabies or poisoning.
Polioencephalomalacia, or PEM, generally occurs when cattle take in too much of the element sulfur, causing rumen microbes to produce too much hydrogen sulfide, the gas commonly known for its smell of rotten eggs. When that excess hydrogen sulfide gas accumulates in the rumen gas cap, it gets absorbed into the blood stream, where it can begin to interfere with the cells’ ability to produce energy. Because the brain tends to put some of the highest demands on the body for energy of any organs, it tends to be the first affected by that hydrogen sulfide buildup.
Clinical signs of PEM include blindness and staggering—hence, the old term “blind staggers”—while in its early stages. Acute levels eventually produce an inability to rise and seizures.
The maximum level of dietary sulfur cattle can tolerate is 0.4 percent of the ration on a dry-matter basis. However, other factors confound the ability to simply control for PEM by controlling sulfur.
- Cattle get sulfur through both their feed and water, so you have to consider all sources to control the risk of developing PEM.
- Not all cattle that consume 0.4 percent or more sulfur will suffer from clinical PEM. The makeup of the microbiological population in the rumen, as well as high levels of insoluble forms of copper, iron or zinc can make the sulfur less available, thus preventing high enough levels to trigger PEM.
- Rumen pH levels can also impact the levels of hydrogen sulfide in the rumen gas cap.
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