Managing Parasites with Good Nutrition

For many years, we have also known that protein nutrition can affect a sheep's resilience to gastrointestinal parasites, and it can also reduce the consequences of parasite infections. Therefore, as sheep producers, it is important to pay close attention to what our sheep are eating.

To better understand how nutrition can affect parasitism, we need to take a closer look at what happens within growing animals and reproducing animals. One of the first signs that we see is the reduction in feed intake. Research by Sykes et. Al., 1988, and Coop et al., 1982 found that feed intake is often reduced by as much as 15 to 20%. Another problem occurring internally is the loss of protein and tissue damage in the digestive tract. This relates to decreased efficiency in the utilization of feeds. Both of these cause production losses through decreased growth, decreased milk production, and, to some extent, decreased reproductive efficiency.

Numerous research studies have looked at how to improve production and growth without the use of anthelmintic (dewormer) treatments. These studies found that increasing the metabolizable protein in the diet during periods of protein scarcity enables sheep to become more resilient to parasite infections and may also contribute to the development of immunity to infections. Research examined several protein supplements, including soybean meal, fish meal, cottonseed meal, urea, and dried distillers' grains with solubles (DDGS). Many of these studies have also found a reduction in fecal egg counts over the long term when dietary protein levels were increased.

As animals respond to parasite infections and nutrient scarcity, they allocate how they will use their feedstuffs. Coop and Kyriazakis (1999) state a possible ordering of priorities for the animals. Young, growing animals will tend to focus on maintaining body protein, then acquiring immunity to parasites, then protein gain, and finally maintaining body lipids or body condition. For reproducing animals, they state that maintaining body protein is the priority, followed by pregnancy or lactation, then immune expression, and finally body condition.

So, how can we as sheep producers use this information for our flocks? Certainly, examining nutrition, particularly protein, can be useful in an integrated approach to internal parasite management. Protein supplementation during times of the year when sheep consume lower-quality feed would certainly help sheep to better manage parasites. Increasing metabolizable protein by as much as 20 to 25% was indicated in research by Datta et al. 1998, Donaldson et al. 2001, and Houdijk et al. 2003.

The benefits of increasing protein levels are especially evident in ewes rearing multiple lambs when they are in relatively poor body condition, and in young growing lambs with the genetic potential for fast growth. Further research is needed to determine the optimal protocol for protein supplementation to enhance immunity and resilience against gastrointestinal parasites. For now, producers should monitor protein levels in rations throughout the year to ensure that feeds meet the National Research Council's recommendations.