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When and how to deworm your animals

By Dr Joseph Othieno

All livestock are at risk of internal parasite infestation as long as they are kept on pasture. Management of internal parasites is a major component of herd health that greatly improves production. Low internal parasite load translates to improved appetite, increased weight gain and a healthy animal with a strong immune system. The production losses attributable to internal parasite infestation depend on geographical location of animals, the age, nutrition, presence of other concurrent infections, the season and environmental conditions.

Young animals are affected most by internal worms’ infestation as their growth is hampered greatly. Adult animals may suffer internal worms’ infestation without showing any clinical signs. Nonetheless infestation with worms will lower its immunity and predispose the animal to concurrent infections. An infected adult animal while not showing clinical signs of worm infestation serves as a source of eggs, larvae and worm segments that contaminate the environment.

Animals infested with internal parasites will have diarrhoea, rough hair coat, unthriftiness and bottle jaw (swelling around the neck area), anemia (pale mucus membranes). Strategic deworming refers to a well-planned internal parasite control programme that takes into consideration seasonal parasites burden, geographical areas, pasture types and ages groups. Strategic deworming acts to break the life cycle of worms and subsequently reduced pasture contamination. Strategic deworming will save clinically affected animals from dying, improve production and reduce contamination of pastures.

Understanding the life cycles of internal parasites

It is important to understand the lifecycle of worms for one to apply strategic deworming. Worms normally have their adult forms that shed their eggs, or segments through feaces into pastures. These eggs come with a shell that gives them a trait to stay out in the open without dying. Under favourable conditions – warmth and moist the eggs stay alive for a day or two. These infective forms wait form animals to ingest them by attaching themselves on grass blades. Rainy condition normally aids their movement from dung mounds onto grass blades. The onset of rains is thus a good time to strategically deworm so that the worms are killed at infancy. 

If not killed, the larvae needs just three weeks to mature and start producing eggs completing the cycle. Various worms have their preferred sites which include the lungs, abomasum, the liver and intestines.  The worms eat digested food, suck blood and destroy organ tissues predisposing the animal to other diseases.

Prevention and destruction 

Pasture contamination is a major source for worm eggs. Adult animals are the main sources of contamination while young stock suffer the greatest as their immune systems aren’t yet mature. Pasture contamination can be reduced by rotational grazing, where young stock are introduced in paddocks ahead of the adult stocks. Removing animals from pastures for at least six months and by scheduling deworming at strategic times (strategic deworming).  

[The writer was the Vet of the Year Award (VOYA) winner in 2016 and works with the Kenya Tsetse and Trypanosomiasis Eradication Council–KENTTEC. Email:]      

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