Vet on call: Understanding worms and deworming plan

Last week’s article on deworming goats elicited several reactions, with farmers seeking to know more about deworming.

Worm control is very important because the parasites rob livestock farmers economic gains through lowered productivity, death of animals and loss of money through purchase of ineffective or inappropriate worming products.

Ineffective dewormers are those that are supposed to kill the targeted worms but for one reason or another, they do not as expected.

Such a situation may arise where worms have become resistant to the dewormer hence cannot be killed by the active ingredient in it.

This often happens when a dewormer is used repeatedly for a long period in one area. Some worms, for instance, have developed resistance to Levamisole.

Resistance may also develop when animals are persistently dosed with lower than the recommended dosing rate of a dewormer.

Inappropriate dewormers are not suitable for specific types of worms. An example is a farmer I found using Levamisole to deworm her sheep, yet the worms she had seen the sheep voiding were tapeworms.

There is no way she could ever have gotten rid of the worms because the drug is known to only kill roundworms.

Ivermectins, such as Ivermectin and Eprinomectin, are a group of chemicals that farmers use inappropriately and then realise their animals are not getting free of worms.

The reason is that Ivermectins kill roundworms but not flukes and tapeworms. The two types of worms belong to a class of parasites called flat worms.

Mohammed from Nandi, a dairy farmer, made the following enquiry through e-mail:

“I am writing to seek your advice concerning last Saturday’s article on the basics of deworming goats. Actually, I never knew that worm infestation could cause decreased fertility and abortion. All along I knew it causes poor growth. Personally, I have always tried to deworm my cattle every three months and I have used different dewormers.”

“I have been alternating between Levamisole and Albendazole-based dewormers. I recently (April 12) used a pour-on dewormer with the active ingredient eprinomectin 0.5% w/v. I have even used an injection containing AI-Ivermectin.

Despite all these, I still realise some of my cows have symptoms of worm infestation. They show poor growth, weakness and rough fur. My question is; what is it that I may not be doing right? I have always used a weighing band to determine the weight and dosage of the drug to administer.” “Kindly advice on how I can be able to tackle this worm infestation and if there are any drugs in the market that you can recommend?”

Now, a farmer can only execute a successful deworming programme if she builds good understanding of worms, their impact on livestock and the therapeutic characteristics of dewormers.

PARASITIC WORMS

You see, I will by no means attempt to make doctors out of farmers but farmers reading this article will be able to understand the kind of questions they can ask their animal health service providers if deworming of their animals appears not to be working.

Worms fall into three groups namely the roundworms, tapeworms and flukes. The latter two are also classified as flatworms.

Roundworms are the most prevalent of animal parasitic worms. They are also the worms that cause most damage to the livestock industry.

Roundworms are categorised into various groups depending on where they prefer to reside in the animal body. There are mainly stomach worms, intestinal worms and lungworms.

There are also roundworms that infest the eyes of animals. Some worms like the screwworm may be found in the animal’s skin.

These are actually maggots of some fly species such as the sheep bot fly, which gets into the nose of sheep and can barrow up to the brain and cause death. There are also a few worms that may be found in the blood and heart.

Tapeworms are found in the intestines, liver and other body tissues. The worms in the tissues, other than the liver and the intestines, are usually intermediate stages of the worms that can only mature in their specific hosts where they develop into the mature tapeworm.

A good example is the hydatid worm that can form a fluid-filled cavity in any part of the body. Normally, the tapeworms in the tissues will appear as a clear ball of fluid with a cottonwool-like structure suspended in the fluid.

Flukes are mainly found in the rumen, the liver and bile ducts and the urinary bladder. The best known members of the fluke family are the liver flukes, bladder flukes that cause bilharzia and the rumen flukes that appear not to cause much problem.

Wherever worms are in the animal’s body, they will always cause problems in many ways, including reducing the blood level in the body thereby causing anaemia, damaging tissues, disrupting normal body function as happens with lungworms in the lungs and competing for food with the host as happens with ascarids.

Depending on the degree of the effects of the worms, animals fail to thrive, some become infertile and others will even abort due to inability to feed the growing foetus.

Worms are controlled using good feeding and watering practices for livestock and regular use of appropriate and effective worming products.

There are very few universal dewormers that remove all worms. Products that are effective against all types of worms are usually a combination of two or more chemicals active against different types of warms. A product like Albendazole is a broad spectrum dewormer that kills all the three types of worms.

Ivermectins on the other hand, whether injectable or pour-on, are only active against some types of adult roundworms and their last larval stage called L4.

Such worms include stomach, intestinal and lungworms. They are however not active against tapeworms and flukes.