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All About Worms and Worming

 27. April 2010  liz.hodges@robinsons-uk.com  Help & Advice  (0)
Worming is a routine procedure on most yards, with many insisting on all horses being wormed at the same time to help ensure chances of worm problems are kept to a minimum. If you don’t keep up to date on worming your horse, using the right wormers for the right times of year this can result in your horse developing a worm burden, which is the name given to a group of parasites living inside and off your horse.
This can cause weight loss and poor body condition, colic and even death in extreme cases. Your horse will not be receiving the complete nutritional value of what he intakes, which can cause deficiencies such as anaemia, as well as being a waste of food and money on your part. This can also cause stunted growth in young animals. With a proper worming routine, these can be easily prevented and ensure your horse is happy and healthy, and gaining all he needs from his food intake.There are 3 different types of parasites in horses that can be controlled, roundworms, tapeworms and bots.
Round worms are most common with many different types, the most common being Small Redworm which burrow into the intestine lining and hatch into adults. If they do hatch out, they then lay eggs to be passed out of the horse in faeces and develop into larvae in the field, to be ingested by another horse. If they don’t hatch into adults and remain encysted on the intestinal lining, they can become so numerous that they block the intake of nutrients through the intestinal wall, causing illness and weight loss. These can then hatch as a mass around the end of winter and cause severe illness and even death. The most common species of tapeworm is becoming ever more apparent in UK horses. These worms are found in the space between the intestines and do not have a sex, but have separate sections containing eggs which as the eggs mature are detached and passed out in the horses’ droppings, releasing the eggs. These eggs are then digested by a certain type of mite, and eventually by the horse to start the cycle again. These can cause hair loss, severe colic and death. Bot eggs are seen on the horse before they are ingested, on the forelegs and neck. They look like tiny yellow and cream specks, and either crawl to the horses’ mouth to be ingested when they develop into larvae or are eaten by the horse. These then live in the stomach and are eventually passed out and develop into adults once out of the horse. They can cause stomach ulcers and damage to the mouth.  Wormer ingredients  There are several different types of worming drugs for different parasites. No one wormer can control them all so a worming programme incorporating more than one type of wormer through the year is a good idea for better cover.  What to worm against and when Main worming times tend to be around spring and autumn or winter. Small red worms should be wormed against around November time. This also ties in with worming against bots, which should be done after the first real frost. A Moxidectin wormer will treat both types of worm. Around February you can worm again for encysted small red worm and this will help prevent a spring outbreak of encysted larvae. In spring, so around April time and again in autumn, around October is the right time to worm for tapeworms. You can do this with a single dose of a Praziquantel wormer.  If you use other types of wormer, double doses can be needed, or courses of wormer. If you ask your vet, they should be able to advise on what is best for your horse. Be wary of under dosing your horse, follow weight guidelines carefully and if in doubt, a small overdose is better than under dosing. Resistance If you don’t expose the worms with enough drugs to kill them, this can build immunity in them which will be passed on to offspring, creating a resistant line. These can be very hard to treat, and some strains of worm are already resistant to certain types of wormer. Resistance can also be created when a select few worms are immune to the wormer. The weak parasites are killed off and the ones left to breed are the ones with immunity, creating more immune worms. Wormers with widespread known resistance are Pyrantel, Fenbendazole and Mebendazole based, so unless advised otherwise by your vet, these may not be ideal to routinely worm with. If you use worm counts as part of your control programme, you may not need to worm as often as you can see how much of a worm burden your horse has. This means the parasites are less likely to build immunity to wormers as they are exposed to them less often. However these don’t tell you how much larvae your horse is carrying, so encysted red worms and similar remain without you knowing. As these are one of the more dangerous worm burdens, this needs careful thought before being relied on as an accurate worm control method. Worm control management If you’re worming the whole yard at the same time for the same parasites, worm management can be easy. There are a few extra things you can do to help as well. Good grass management is also needed to help prevent the spread of worms, so poo picking the fields at least a few times a week is a must. If you keep on top of it, it’s far easier too. Also making sure that new horses are wormed and kept in for 48 hours after before they go out on the same grass is a good idea to kill any worm burden they may have. Try not to overstock fields as this can increase the worm burden of the land and therefore the amount your horse ingests.
If you can, grazing other livestock on the land and rotating fields with them helps reduce worm burdens as animals like cows and sheep destroy the larvae naturally as they ingest it, cleaning the area for horses. This isn’t always practical but a good idea if you can do it! 

Worming correctly can be a bit of an art, so if you’re unsure consult your vet for advice and do plenty of reading up to make sure you’re doing it right.
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