Risk of sulfate toxicity grows as drought deepens

As we deal with drought conditions in many areas of the Prairies, water quality that cattle drink may also be affected.

Sulfate is a common mineral component and is present at some level in most water sources, as well as in many feeds.

Some areas of the Prairies may have wells with high levels of sulfate that can affect animal performance.

However, during a drought, water that may have been acceptable for animal consumption may become toxic as the summer progresses.

Evaporation can lower water levels in dugouts throughout the summer, especially during drought, and can begin to concentrate mineral levels.

The most common form of water toxicity seen in cattle in Western Canada is sulfate toxicity.

Water that is high in sulfates is not very palatable to cattle and if given a choice they will choose another source and refuse to consume the high sulfate water.

However, if there is no other water source, the cattle will eventually drink the high sulfate water and can show signs of toxicity.

Even then, cattle may reduce intake, drink reluctantly and can be observed attempting to drink but allowing water to dribble out of their mouths.

The palatability of high sulfate water might be very poor, but thirst is an even stronger motivator and cattle will eventually drink it.

There are many good guidelines for livestock water quality available but a general rule of thumb is that water with less than 1,000 parts per million (p.p.m.) of sulfate is acceptable for beef cattle to consume.

Once sulfate levels are between 1,000 p.p.m. and 2,000 p.p.m, effects on animal growth and performance can be seen.

Sulfate interacts and binds with copper, making it unavailable to the animal. This can result in a copper deficiency, which is sometimes referred to as a “secondary copper deficiency” caused by the antagonism of the sulfate mineral in the water or the diet.

Copper deficiency can create low growth rates, impaired fertility, anemia and hair colour changes. Many areas of the Prairies already have forages low in copper, which results in low copper levels in cattle that consume these forages.

Preliminary results from our Western Canadian Cow-Calf Surveillance Study have shown that most cows sampled in our study had below adequate levels of copper. Many herds had less than half of the sampled cows with adequate copper levels.

If we compound a situation that already has marginal copper levels by adding water with sulfates greater than 1,000 p.p.m., we can create a secondary copper deficiency that will cause significant deficits in cattle growth and fertility.

As sulfate levels in water climb higher, other signs of toxicity become evident.

If water sulfate levels are more than 2,000 p.p.m., we may begin to see signs of nervous disease in the cattle. Polioencephalomalacia (PEM) is the technical term for a nervous disease of cattle that is characterized by blindness, difficulty walking and seizures.

Eventually, the animals become recumbent and may die. Some animals with less severe forms of PEM may recover but have some minor neurological symptoms.

The disease was first described in the 1950s and was thought to be caused by a deficiency in thiamine. Thiamine levels are very difficult to determine in cattle and recently it has been shown that sulfate toxicity can create PEM and is probably the primary cause for the disease.

If the animal consumes water or feed with exceptionally high levels of sulfate, hydrogen sulphide gas is created in the rumen and is absorbed into the blood stream.

Hydrogen sulfide has a toxic effect primarily on the brain and the result is an animal showing the many nervous system symptoms of PEM.

If water sulfate reaches the 3,000 p.p.m. level or the 4,000 p.p.m. level, the development of PEM be-comes even more likely.Lack of water consumption due to water quality can also result in salt toxicity. Generally, animals can tolerate high concentrations of salt or sodium in their diets if they are able to access and drink adequate fresh water.

If water quality deteriorates to where water is unpalatable or unavailable, animals can also be affected by salt toxicity, which can be manifested as abdominal pain, diarrhea,and nervous signs such as circling, loss of balance and seizures.

High sulfate feed can also contribute to the total dietary sulfate levels and so sulfate levels in the diet may need to be considered.

Ethanol byproducts such as dried distillers grains with solubles have high levels of sulfur, and feedlot cattle that consume these types of feeds and are exposed to moderate levels of sulfates in water may have total sulphur levels high enough to create an outbreak of PEM.

There is no specific treatment for PEM and many veterinarians will use thiamine and anti-inflammatory drugs as supportive therapy. Removal of animals from the water or feed source that is high in sulfate is essential.

Water can easily be tested for sulfate levels, and in dry summers it is important to monitor dugouts because their sulfate levels may increase as evaporation occurs.

A livestock agrologist, veterinarian or nutritionist can assist with water testing and interpreting results.

John Campbell is a professor in the department of large animal clinical sciences at the University of Saskatchewan’s Western College of Veterinary Medicine.

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