Effective management practices for parasite control in cattle

Tim Nickel - Bovine Technical Services Veterinarian, Boehringer Ingelheim Animal Health Canada Inc.

Article Summary:

• In any robust parasite control program, there should be both management and treatment options.
• Gastrointestinal worms are a hidden problem that can be easy to forget.
• Optimal stocking density can help reduce the spread of parasites from animal to animal.
• Pasture management – rotational grazing, grazing younger animals before older ones, and resting pastures – can also help limit parasite loads.

Parasites such as flies, lice, mites or worms can affect the health and performance of cattle. Developing and implementing a parasite control program can help minimize this impact. There are several control strategies available to producers and below are details about some non-chemical options.

Having animals in good body condition and on a diet that meets all of their nutritional requirements is the most effective way to reduce the impact of parasites, both internal and external. Animals that are thin or have nutritional deficiencies, including minerals and vitamins, are more susceptible to the impacts of parasites. They are also more prone to other diseases. It is why animals are often more affected by parasites in situations like a long cold winter or during a drought, when nutrition may be less than optimal. Feed testing and correction of any deficiencies can go a long way to making animals better able to cope with parasites.

Overcrowding is another important risk factor. External parasites are more likely to spread when animals are in close proximity. Lice are a good example of this. They are spread mainly through direct contact between animals, and the more crowded animals are the more readily they can spread amongst a group.

Stocking density also affects internal parasite loads. Worms are picked up by animals as they graze on pasture. Overcrowding leads to more manure build-up in the environment, which leads to increased contamination of pastures with infective worm larvae. In addition, when stocking density is high, animals tend to graze closer to the fecal pats where the infective larvae are most concentrated. This leads to higher worm loads in the animals. By reducing stocking density there is less contamination of the environment with infective larvae and less grazing close to the fecal pat, resulting in lower worm burdens in the animals.

Pasture management also plays a big role in internal parasite control. In addition to lowering stocking density, pasture rotation is another tool that can be utilized. The vast majority of the infective larvae are found on the lower part of the plant, close to the ground. If animals are moved before they graze below this point, it will limit the level of exposure. As well, if pastures are to be grazed more than once in a season, consider the sequence. Grazing younger animals first followed by older animals will save the cleaner pastures for the younger, more susceptible animals. Older animals have usually acquired some immunity to worms over several grazing seasons and will be impacted less by the larvae remaining on the pasture after the young animals have grazed.

When possible, leaving pastures empty after initial grazing will also help to lower worm loads. The more time at rest, the fewer larvae that survive. The only way larvae complete their lifecycle is when they are ingested by an animal, where they can then develop into adults and reproduce. While some larvae may still survive in the subsoil, their numbers will be greatly reduced.

A different species, such as sheep, can be grazed after cattle, to reduce the cattle parasites present on the pasture. This is because cattle-adapted worms do not survive as well in other ruminant species, and vice versa.

The individual animal’s genetics can make them more susceptible to parasites. It is generally accepted that 20% of animals in a group harbour 80% of the parasites, and there is some evidence to indicate at least some of this is due to genetics. The goal would be to identify these individuals and cull them from the herd. Unfortunately, this is not easily done given the current tools we have, but technology is changing rapidly, and it may become more feasible in the near future.

Talk with your veterinarian to help develop a comprehensive parasite control program that suits the specific circumstances and needs of your operation.