Drought brings additional livestock challenges

It appears substantial areas of the Prairies have potential to experience significant drought once again this summer.

Years in which we have significantly less than normal rainfall can have major effects on pasture quality and forage ability. As well, the impacts on animal health can be significant and far ranging.

First, we should have major concerns about water quality on many areas of the Prairies. During a drought, water that may have been acceptable for animal consumption can become toxic as the summer progresses. Evaporation can lower water levels in dugouts throughout the summer and especially during a drought can begin to concentrate mineral levels.

In those geographic areas that have been dealing with low moisture for several years, the dugouts and water sources may already be quite high in sulfates even before the heat of the summer occurs.

Sulfate toxicity can impair copper absorption, causing a copper deficiency that results in low growth rates, impaired fertility, anemia and hair colour changes.

At higher levels of sulfate (more than 2,000 parts per million) we may begin to see signs of nervous disease in cattle.

Polioencephalomalacia (PEM) is the technical term for a nervous disease of cattle characterized by blindness, difficulty walking and seizures. Eventually, the animals will become recumbent and may die.

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

Electrical conductivity meters, if used correctly, can provide a quick estimate of water quality before sending samples to the laboratory. Your local livestock agrologist, veterinarian or nutritionist can assist you with getting your water tested and interpreting the results.

Blue-green algae may become more common when we have warm daytime conditions during the summer. This cyanobacteria can live on the surface of stagnant, nutrient-rich water bodies such as dugouts and will appear with a blue-green sheen on the surface of the water, which appears like green paint or curdled greenish milk.

Strong winds can cause the algae to accumulate at one end of the dugout or water body and when the algae die they can release potent neurotoxins that can rapidly kill the animals.

Dugouts can be treated with copper sulfate to kill the blue-green algae, however, it is critically important to recognize that cattle should not be given access to the dugouts for 12-14 days after the treatment has been administered to the water. The algae that have been recently killed are releasing toxins during this period.

A variety of plant toxicities are much more likely during seasons of drought. Cattle that have limited grazing are more likely to consume plants that they would normally ignore in more lush grazing situations. Grain aflatoxins are sometimes higher in plants such as corn when stressed. Nitrates and cyanide may be higher within stressed plants as well.

In addition, producers are sometimes forced to use novel feeds that can sometimes also have toxic components. For example green flax has high levels of a toxic compound known as cyanogenic glycoside, which can be converted to prussic acid when the plant is damaged by drought, wilting, or other trauma such as animal trampling.

Fog fever is a common name for a specific pneumonia of adult cattle. Outbreaks of fog fever are most commonly associated with moving cattle from dry-stressed pastures to more lush grazing. We have also seen outbreaks occur in areas that have received significant lush regrowth after a prolonged dry spell.

Outbreaks usually occur 10-14 days after cattle are exposed to the more lush grazing conditions. The pneumonia that develops is unique from many of the other pneumonias that ranchers are familiar with.

The respiratory syndrome is caused by a protein in the lush pasture called tryptophan. When the cattle are exposed to higher levels of tryptophan gradually, and their rumen bacteria are not adapted to this protein, this protein is converted by the bacteria in the rumen and produces a toxin known as 3-methyl-indole that is circulated in the cow’s bloodstream to the lungs. Once the toxin reaches the lungs it causes severe cellular damage and the result is a severe, untreatable respiratory syndrome.

Vitamin A levels can also be affected because of drought conditions. The relationship of vitamin A levels to drought is well established and a recent western Canadian study showed that vitamin A levels were significantly lower in herds that were in geographical areas that had less than 200 millimetres of rain in the previous growing season, compared to herds that grazed where there was adequate precipitation.

Newborn calves get almost all of their vitamin A from the colostrum they consume shortly after birth. They are actually born with very low levels of vitamin A and are reliant on their dam’s vitamin A levels in her colostrum.

If a cow has been grazing under drought conditions or fed stored feeds low in vitamin A and not received adequate levels of supplemental vitamin A, the calf will be at a much higher risk of being deficient in vitamin A. Vitamin A is necessary for adequate immune function and normal growth. Studies have demonstrated that the calves deficient in vitamin A were almost three times more likely to die than calves that have adequate levels of vitamin A for their age.

You might want to consider supplementing your cows and calves with vitamin A this year to prevent deficiencies.

The consequences of decreased body condition and reproductive performance during drought must also be considered. Cattle with fewer feed resources during the grazing season will be at risk of lower body condition.

Numerous research studies have shown the impact of body condition on fertility. By 70 days after calving, only 55 percent of thin cows will have started cycling again compared to 96 percent of cows that are in good body condition.

In addition, the first service conception rates may be as much as 20 percent lower for thin cows. The results are dramatic and can have significant effects on the pregnancy rate in the following year. If cows aren’t cycling, they cannot get pregnant.

This problem may take another year to manifest itself if cows go into this grazing season in reasonable body condition or it may appear as lower pregnancy rates in this year, if the cows are already in borderline or poor body condition.

Drought always creates significant challenges for our industry and preventive strategies and solutions to protect animal health are possible but often logistically difficult.

Consult your veterinarian, nutritionist or local livestock agrologist to determine which strategies would be the best fit in your situation. Let’s hope that a few good rains will prevent all of these issues from occurring.

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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