Internal parasites are the greatest single causes of colic in horses and are often a causative or contributing factor in many respiratory, digestive and performance problems. Though parasites are a constant problem for horse owners, the severity can be lessened. The following information can help you to reduce the risk of worm infections in your horse.

The four most common internal parasites in horses

• The most harmful of these are the large and small strongyles (Redworms and Bloodworms). They are approximately ½ inch long (1cm) and reddish in colour. The larval forms of these parasites may damage the blood vessels and other organs. Young horses are particularly susceptible to large infestations. Equine worming programmes are mostly aimed at the control of large and small strongyles.
• Ascarids, or Round Worms, are stiff, white and up to a foot long (30cm) in the adult stage. Young foals from 132 weeks to one year are most vulnerable.
• Pinworms are about 1 ¾ inches long (4.5cm) and are long, thin and occur in the rectum. Pinworms cause irritation - the horse will rub its tail. A discharge will be present and pinworms may be visible around the anus.
• Bots (gasteropilus) are the larvae of botflies. The yellow eggs are laid on the hairs on the front part of the horse, within reach of his tongue. The eggs hatch in 10 to 14 days and the horse will lick them off his coat and transfer them to his mouth, where the larvae burrow into the mucous membranes of the lips and gums. There they remain for a short growing period before passing on to the intestine where they attach to the stomach wall. They remain there for almost a year before passing out with t he faeces to pupate in the soil. Adult botflies then emerge from the pupil case in 3 to 9 weeks, depending on the temperature.

Resistance

All over the world parasites develop resistance against wormers. When resistance develops the parasite will no longer be susceptible to that wormer. Because of high research costs there are no new types of wormers being developed. Therefore it is important to prevent the parasites surrounding your horse to develop resistance. There are several things you can do to prevent this.

• Remove manure daily from you paddocks, yards and stables.
• Only worm you horse when it is necessary. At you VetEquine Otago office in Mosgiel we can perform a faecal egg count for you. This shows if you worming programme is successful. Basically there should be no worm eggs up to 6 weeks after worming
• Do not ‘under-dose' your horse when worming
• Use the correct type of wormer against the right type of worm. Not all worms are susceptible to the same type of wormer, after performing a Faecal Egg Count, your vet at VetEquine can tell you which type of wormers are best for you horse.
• If you bring a new horse in on your property, make sure you have it tested for worms and if necessary treated to prevent it from infecting other horses.

Faecal Egg Count

At VetEquine Otago we are equipped with a testing lab, where we perform faecal egg counts. All it takes is to bring in a sample of fresh manure from your horse and we can tell you if the wormer you used is still effective and if your horse needs to be wormed again.