The Hidden Cost of Parasites in Cattle


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

Article Summary:

  • The impacts of external parasites are easy to see but are not the only type of parasite cattle deal with.
  • Gastrointestinal worms are a hidden problem that can be easy to forget.
  • Gastrointestinal worms are present in virtually every operation.
  • They can keep animals from realizing their full potential and result in reduced profitability.
  • Understanding the seasonality of parasites is a key factor in developing control strategies, especially with regards to timing of interventions, as it can play a major role in the success or failure of these programs.

In cattle, sometimes it is easier to appreciate the impact that external parasites such as flies or lice have on an animal. They are either visible or they result in signs that can be readily observed, such as scratching and hair loss. These parasites can have an obvious impact on the health and welfare of the animal, especially when they exceed certain thresholds. Aside from the obvious outward signs, animals may also have changes in behaviour including reduced feed intake as a result of the constant irritation caused by these pests. These parasites often have a seasonal occurrence. Lice are most active in the winter while fly numbers peak in mid to late summer Knowing this information is important, as it points to when control strategies should be done.

When it comes to internal parasites, it is harder to appreciate their presence and impact. Gastrointestinal worms, or nematodes, are picked up by the animal during the grazing season in the form of larval stages that reside on pasture. As with flies and lice, there is a seasonality to these parasites. Levels build as the grazing season progresses, both on the pasture and subsequently in the animal. The highest levels occur in late summer and early fall.

These nematodes are a hidden threat. They are not readily visible and special tests are generally required to confirm their presence in animals. As well, the worm burdens that are typically seen in Canadian cattle rarely result in obvious clinical signs. However, subclinical effects such as reduced feed intake and feed efficiency are common.

As a result, young growing animals have lower weight gains while older animals may have loss of body condition. These nematodes can also suppress the host’s immune system, which may make animals more susceptible to infections and decrease response to vaccination. Breeding animals infested with worms may have reduced fertility affecting the reproductive performance of the herd. All of these effects can add up to significant economic losses in an operation.

A recent study1 that assessed the presence and abundance of gastrointestinal worms in cow-calf operations in Western Canada showed that they are widely distributed. Every herd that was sampled and even a high percentage of individual animals, were positive for worms. Parasite numbers were lower than some parts of the world. However, based on this data, it would be fair to assume a Canadian herd has worms rather than assume they are worm-free. One of the few exceptions would be in animals that have no access to pasture or grass, as the worms can only be picked up through grazing. This may be true for many of our dairy farms, but it would be rare in our beef herds.

We have given you a lot to consider. It’s best to work with your veterinarian to develop and implement a parasite control program for your herd.


  1. De Seram EL, Redman EM, Wills FK, de Queiroz C, Campbell JR, Waldner CL, Parker SE, Avramenko RW, Gilleard JS, Uehlinger FD. Regional heterogeneity and unexpectedly high abundance of Cooperia punctata in beef cattle at a northern latitude revealed by ITS-2 rDNA nemabiome metabarcoding. Parasites & Vectors. 2022 Dec;15(1):1-1.


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