Worming
Good pasture management is essential to prevent worm problems. Horses can have a small number of worms living their intestines, without any adverse affects, however, if the worm number is allowed to increase a number of problems can be seen including ill thrift, colic and diarrhoea. By using a good worming protocol and pasture management these worms can be kept under control preventing future problems.
Types of worm
1.Redworms:
These can be divided into large redworms (strongyles) and small redworms (cyathostomes). Both these parasites colonise in the intestines after the horse grazes contaminated pasture. Here they evolve into adults, producing eggs passed in the droppings to further contaminate the pasture. The large redworms migrate as larvae through the intestines and liver, before become adults, causing inflammation. The small redworms can go into cysts in the intestinal wall to hibernate over the winter to emerge again in the spring. This is the dangerous time for horses as the mass emergence of larvae can cause severe damage to the intestines. This condition is known as larval cyathostomosis (see section on diarrhoea).
2.Tapeworm:
The tapeworm, anoplocephala perfoliata, lives at the junction between the small and large intestines, ileo-caecal junction. Tapeworm infestation can cause varying degrees of colic.
3.Bots:
Bots, gasterophilus, live in the stomach of horses as larvae. These are later passed in the droppings and hatch out into adult flies. These flies then lay their eggs on the horses coat, especially legs. The larvae can cause stomach ulcers.
4.Lungworm:
The larvae of lungworm, dictyocaulus arnfieldi, migrate to the lungs and can cause respiratory disease. This is seen very rarely, however, horses that live with donkeys are at greater risk.
5.Strongyloides westeri:
This worm can be transmitted from the mother to her foal in the milk and can cause severe diarrhoea if the foal is weak with a poor immune system.
6.Parascaris equorum:
This worm usually affects younger animals.
Diagnosis
A veterinary surgeon can often assess that worms are a problem in horses with the typical signs such as ill thrift, colic, diarrhoea and weight loss alongside inadequate worming and poor pasture management, however, samples of the droppings can be used to count the number of worm eggs. A blood sample is also available to help diagnose tapeworm infestation.
Prevention
1.Good pasture management: The pasture should not be overcrowded and droppings should be regularly picked up.
2.If it is possible grazing with other species such as sheep or cattle should be done in rotation. Parasites from these species don't affect horses and their droppings promote good grass growth.
3.New horses should be wormed on arrival and should be stabled for two days before going onto the pasture to reduce contamination.
4.All horses on the pasture should be wormed regularly to reduce the number of eggs passed in their droppings.
Frequency of worming
Worming regimes should be set up for individual horses. One major problem we face at the moment is the threat of worms becoming resistant to certain wormers, caused by improper worming. To prevent this worming should be minimised where possible. The main method to minimise worming is to take faecal samples and count the number of worm eggs present, this can be done at most large equine vet practises. Horses with high numbers should be wormed, however, if the numbers are low then worming is not necessary which reduces cost and build up of worm resistance. This technique works very well on small yards where there are not many horses present and few new horses are introduced. For large yards and studfarms the reduction in worming can be more complicated as there is usually more contamination of the pasture. In these cases worming every 8-12 weeks is often necessary. It is very important that all animals are wormed at the same time and are following the same protocol. The best option is for the yard manager to formulate a worming protocol with the help of a veterinary surgeon for all the horses.
Types of wormer
1.Ivermectin and Moxidectin: These wormers will kill almost all types of worm, including bots, however, are not effective against tapeworm. Although ivermectin has some action against the hibernating cyathostome larvae they will not kill all of them and moxidectin has been seen to be far more effective. Moxidectin also has a longer lasting effect, therefore, can be given at three monthly intervals, however, should not be used in foals.
Trade names:
Ivermectin: Eqvalan, Noromectin, Panomec3.Moxidectin: Equest Ivermectin and Praziquantel: Equimax
2. Fenbendazole: This wormer is effective against most species of worm, however, reststance has built up against cyathostomes. Fenbendazole can be given as a 5 day course to target hibernating larvae and is a safe course of treatment if the animal has not been wormed for a long while or the worming history is unknown.
Trade name: Panacur, Panacur equine guard (5 day treatment)
3. Pyrantel: Is reasonably effective against many mature worms, however, is mainly used as a treatment against tapeworms at double the dose.
Trade names: Strongid-P and Pyratape-P.
4. Praziquantel: This is a specific treatment against tapeworms.
Trade names: Praziquantel: Equitape. Praziquantel and Ivermectin: Equimax
Worming method:
1.Pick one class of drug to use for one to two years as your routine wormer and then change to another the following year to help reduce resistance.
2.Use this wormer throughout the year when the faecal egg count results indicate that the horse needs worming or, if this is not possible e.g. large yard, treat at intervals recommended by the individual wormer.
3.Treatment against tapeworms should be given in the autumn. Either praziquantel or a double dose of pyrantel.
4.To help prevent problems with encysted cyathostome larvae horses should be treated with either moxidectin (Equest) or a 5 day course of fenbendazole (Panacur Equine Guard) in the Autumn.
5.Ivermectin should be given in December to treat bots.