With the increase in rainfall and the lush pastures, I have noted a dramatic increase in parasitism in both cattle and small ruminants. As a veterinarian, I am often asked, “What is the best way to treat for worms?” While at first this seems like a simple, straightforward question, the answer is very complex and varies with each individual farm.

The largest group of parasites we deal with are intestinal nematodes. These parasites are transmitted through oral ingestion of larvae that live in water droplets at the base of forage plants. These larvae hatch from eggs that are shed in the manure of parasitized animals in the herd. A single adult Ostertagia female can lay up to 100 eggs per day, so an infested animal can shed thousands of eggs into a pasture daily. Once these eggs hatch, the larvae live in the base of grass plants and are ingested as animals graze. The complete life cycle of most intestinal worms is three weeks; larvae can cover themselves in a protective cyst and survive in the pasture environment for weeks or months and wait for ideal, moist conditions to become active.

Another prominent group of parasites are coccidia. These are protozoal parasites that are transmitted by oral ingestion in manure contaminated environments. Young animals are most susceptible, but older animals can be adversely affected if infested with enough organisms. Coccidia are species specific; coccidia that affect birds do not affect ruminants or pets. Like intestinal nematodes, coccidia can produce thousands of offspring that shed in the manure of infested animals.

Diagnosis of parasitism consists of collecting manure samples and having the samples spun down and checked for egg counts by a veterinarian. Individual animal or composite samples of a group may be appropriate, depending on the situation.

Once a diagnosis is made, treatment regimens can be designed for the individual herd or flock. Deciding on a dewormer is based on the types of parasites, the type of animals being treated, and the treatment history of a particular farm. In some instances, it will be recommended to treat the entire group. Other times, treating individual animals is the most appropriate method. One of the primary problems that I run into is drug resistance. Resistance to anthelmintics is common, particularly in small ruminants. Newer research indicates that dosages of medications given to small ruminants needs to be higher than in cattle. Resistance has progressed at a higher rate due to several factors, including inappropriate dosing, deworming too frequently, and using the same product without changing. When changing dewormer, it is important to change to a class of dewormer that is chemically different than what was previously used.

One way to monitor animals is to evaluate the inner eyelids for color. Anemia due to blood loss caused by parasites is indicated by a decrease in the pinkness of the mucus membrane of the eyelid. Other symptoms owners need to watch for include fluid accumulation underneath the jaw (bottle jaw), poor hair coats, poor weight gain and diarrhea. Periodic fecal examinations are another way to monitor egg counts and assess if deworming is needed.

Take the approach that management of the environment along with strategic deworming and fecal egg count monitoring is the best approach to assuring your livestock remain healthy and develop to the best of their ability.

Dr. Mike Bloss, DVM, owns and operates Countryside Animal Clinic with his wife, Kristen Bloss, DVM. The mixed animal practice is located in Aurora, Mo.


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