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Worming Regimes:
What are the options and which is best?


A. Standard interval worming



-Simple and easy to follow in practice, especially on large yards; all horses are wormed on set dates

-Helpful to prevent worm burdens when there is a high turnover of horses or pastures are ‘horse-sick’

-Reduces the risk of infestation in your horse even if it shares a pasture with untreated and potentially infected horses


-Many horses have low worm burdens and may be treated un-necessarily; this is a waste of money

-Resistance to the worming drugs is encouraged -

The drugs used to worm horses can be detected in their faeces; these in turn can kill some wildlife (eg. insects)


An example of a standard interval worming schedule:



Most of the discussion about resistance focuses on redworms but in reality it also applies to tapeworms too. Infection with tapeworms is usually assumed with the above schedule, and they are killed by the ‘pramox’ component of Equest. The following year different wormers would be used to try to reduce resistance.


B. Targeted/intelligent worming


-Worming is restricted to horses that have positive worm egg counts (see below); this reduces the amount of drugs used and cost

-Using fewer drugs reduces resistance to them

-Horses with a high worm burden can be identified which helps to manage their pasture companions pro-actively

-More environmentally friendly



-Motivation and planning is needed to monitor the worm burden of the horses grazing the pasture and faeces samples needed to be collected at appropriate times


An example of a targeted worming schedule:




Important points

Horses are usually treated when the worm burden is greater than 200 eggs per gram For the above programme to work, all horses grazing together need to be on the same schedule Droppings must be collected regularly Clean grazing is required The annual blood test assesses the need to treat for tapeworms based on the antibody level.







These are also known as small cyathostomes and are found in the horse’s large intestine. The larvae live in the gut wall and develop into adults that lay microscopic eggs that are passed in the faeces. Redworms can cause colic, weight loss, diarrhoea or general ill thrift. Elderly or young horses are particularly prone to disease. Worm egg counts performed on faecal samples will detect adults laying eggs. Larvae can ‘over-Winter’ in the bowel wall and suddenly cause damage when the conditions are right. For this reason it is important to use a wormer in the Winter thar kills the larvae (eg. Panacur Guard or Equest) even if the worm egg count is negative.



In contrast to their effects in other animals, tapeworms in horses do not generally cause weight loss. The adult worms can be found in both the small and large intestine. Heavy infestations (as shown in the picture below) can cause blockages that result in spasmodic and impactive colic. Tapeworm segments are shed intermittently in the droppings, and hence a faecal examination is an unreliable way to detect infestations. A blood test is more reliable at detecting the presence of tapeworms and will give a guide to the level of infestation.



Bot flies lay eggs, usually on the lower legs in the autumn. These eggs are then swallowed when the horse grooms itself and grub type larvae develop in the stomach: Large numbers may cause irritation with discomfort resulting in colic. Therefore during December we advise using a product such as Vectin or Equest that will kill the larvae



These large roundworms can cause problems in foals, where infection is transmitted by eggs passed in their mares’ droppings. Larvae develop in the gut, where large numbers can cause obstructions and colic. The adults resemble spaghetti:



Pinworms are uncommon and live in the rectum. Adults lay eggs on the skin around the anus resulting in irritation. Affected horses rub their hindquarters and tailheads in a similar manner to those with sweet-itch. A single dose of an ivermectin based wormer (eg. Vectin) or Equest will kill the adults.



These worms require a donkey to complete their life-cycle. Therefore all donkeys and any horses kept with them should be treated at least yearly for lungworm.

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