Warm, wet weather poses parasite problems for pets


I am very pleased to be writing a new column for the Weekly on veterinary and pet care topics. Each month I will feature a topic that is of interest to you, so please contact me at the email address listed below with questions related to veterinary or pet care. I will do my best to feature your questions in upcoming articles.

This time, we will start out with parasites, a common spring and summer nuisance — especially for grazing animals.


Cindy Mendive

A week-old foal nurses from its mother. Young animals are most at risk from infection and can often get worms from their mothers.

Spring is a magical time of year for veterinarians, with newborn calves, lambs and foals being born. The weather is warming, making outdoor calls more pleasant, and April and May showers are turning pastures green and lush. However, the warm, wet conditions are also a recipe for a less pleasant thing: parasitic worms.

Parasites come in a huge variety, and many are species-specific. The most common and well-known parasites commonly called worms include tapeworms and roundworms. They do damage by disrupting the lining of the gut, and cause abdominal pain, diarrhea and fluid loss leading to dehydration. Many of these worms are blood suckers and can cause significant blood loss and anemia. Other classes of parasites include external ones such as lice, flies, fleas or mites, which tend to damage the skin and hair coat.

Each animal species has different signs when infected with parasitic worms. In horses we most commonly tend to see signs of colic and weight loss. In cattle we see diarrhea or scours and a failure to gain weight as expected for the age of the animal. Sheep and goats are especially susceptible to worms, and even as adults do not develop very good immunity to infection.

In small ruminants diarrhea is rarely a sign. More commonly they tend to go off their feed, then become very weak and anemic, and are often unable to stand. At this stage, the worms often have done significant damage, so this becomes a true emergency. Cats or dogs commonly have diarrhea, and owners may even see tapeworm segments around their pets’ rear ends. As a side note, we routinely deworm young puppies and kittens because they are often born with worms they acquire either in the womb or when nursing.


Virginia Cooperative Extension

The life cycle of a typical stomach worm.

To reduce parasites in your animals, it is important to understand their general life cycle. Parasites have four phases in their lives. Phase one is the parasitic phase, where the parasite is present in the animal and is feeding and reproducing. Phase two is the contamination phase, where eggs from the adult worms are passed via feces onto the pasture or environment. Phase three is the free-living phase, where these eggs hatch and become larvae and begin to develop on the pasture. This phase is dependent on warm, moist conditions, especially in spring and early summer. Phase four is the infection phase, where the animal consumes the larvae and thus becomes infected, and the life cycle repeats itself.

When we use de-wormer medication, we are going after the adult worms in the animal in hopes that we will stop these worms from reproducing and contaminating the environment with eggs. And by using the same de-wormers over and over we run the risk of having worms on our pastures that are resistant to our deworming products.

To try to avoid resistance and better target our medications to the animals that really need it, we like to run a fecal egg count at the veterinary practice, by which we determine the level of parasitism in individual or groups of animals. If it is a very light load we will often recommend not deworming the animal. If it is a heavy load of parasites we may recommend a deworming product targeted for the types of worms the animal is infected with.

To reduce the free-living parasites not affected by our de-wormers, we rely on a technique called pasture rotation and management. There are a number of different strategies; each is dependent on the landowner’s animals and amount of available pasture. The idea is to provide clean, safe pasture with a small amount of parasitic eggs and larvae to the animals most at risk of infection, such as young animals. We then graze the same pasture with animals likely to have more natural immunity to parasites, such as older animals. Another important component is keeping fecal contamination of pastures to a minimum and avoiding feeding animals in areas with a large amount of contamination. I recommend contacting your veterinarian if you are interested in setting up a personalized parasitic control program for your property.

With proper management and targeted deworming strategies, we can reduce our grazing animal and companion animals’ exposure to and potential illness from these debilitating and sometimes deadly little parasites.

Dr. Jamie Arndt is an associate veterinarian at the Animal Clinic of Walla Walla who practices mixed animal veterinary medicine. She can be reached with ideas for upcoming articles at thevetviews@gmail.com.


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