By Sarah Whyte

Ontario producers should consider supplementing their animals’ diets with vitamins and minerals according to researchers from the Animal Health Laboratory and the Ontario Veterinary College at the University of Guelph.

The research team, headed by Dr. Brent Hoff, tested the blood and liver of 55 Ontario beef cows for Vitamin E and six minerals: selenium, copper, iron, manganese, molybdenum, and zinc. All of the cows were found to be deficient in at least two elements.

Vitamins and trace minerals are essential to animal health, just as they are essential to human health. In cattle, they optimise growth rate, reproduction rate, feed efficiency, and immune function—all translating into animal wellness and cost efficiency.

There is cause to suspect that mineral deficiencies may be common in Ontario cattle. Research has shown that most grains and forages grown in the province do not contain enough selenium, copper, zinc, or manganese to meet the dietary requirements of cows.

Unfortunately, because the effects of deficiency are subtle, it can be difficult to tell when animals are not getting enough vitamins and minerals. Slowed growth and low feed efficiency can easily go undetected by both producers and veterinarians.

Even with testing, veterinarians have a hard time diagnosing mineral deficiencies because blood samples can be misleading. For example, the amount of copper in a cow’s blood is not a reliable index of the amount in her liver. Infection, trauma, gestation, and the animal’s diet can all influence the amount of a mineral that shows up in the blood.

Dr. Hoff’s research team set out to determine if mineral deficiencies are, in fact, a problem in Ontario herds. They performed vitamin E and mineral testing on blood and liver samples collected at slaughter from 55 Ontario beef cows of unknown health status.

The average levels of Vitamin E and selenium were below the adequate range for both blood and liver (these values are highlighted in table 1). Most animals tested had low blood levels of selenium, copper, and manganese. Significant variation was found among the animals tested, though, and in some cases levels were well above the required range.

In a second test, the researchers supplemented the diets of five Ontario beef herds with selenium for three months. They then tested the blood selenium and vitamin E levels in six herds, including the two that had received supplements. The supplemented herds were the only ones not deficient in selenium. However, the average level of vitamin E was still below the adequate level in the supplemented herds.

Table 1. Vitamin E and trace mineral levels in 55 Ontario cull beef cows at slaughter

The studies provide strong evidence that deficiencies, particularly of vitamin E and selenium, are common among Ontario beef herds. Other mineral deficiencies are also prevalent. To ensure adequate nutrition and performance, producers should consider feeding their livestock vitamin and trace mineral supplements.

According to the researchers, producers who have used mineral supplements have seen improvements in the health, growth, and reproductive performance of their animals.

It is possible to get too much of a good thing, though, so producers should proceed with supplements cautiously. All minerals can be toxic if consumed in excessive amounts. The researchers suggest those occasional tests of feed, blood, or tissue levels would help to prevent over-supplementation.