Prolonged grazing over the summer will mean that horses will have been heavily exposed to parasite infection. Hopefully this exposure will have been reduced through routine roundworm control and removal of dung from the pasture.

However, it is in the autumn that attention needs to be turned once again to controlling tapeworm; previously controlled 6-months earlier in the spring. Although tapeworm show no strong seasonality as to when they infect horses, exposure is greatest during periods of prolonged grazing1.

In addition infective larvae of the small redworm (the most common of parasites present on the pasture) that are ingested as the horse grazes during the autumn will, once they have burrowed into the horse's gut wall and formed a cyst, increasingly become dormant - known as inhibited encysted small redworm larvae. It is these inhibited encysted small redworm larvae that may develop and emerge from the horse's gut wall en-masse in late winter/early spring. This mass emergence can result in diarrhoea, rapid and severe weight loss, or colic, and is potentially fatal, with a 50% mortality rate2.

Autumn Worming Treatments:

Routine Roundworm Control: Continue to routinely treat against roundworm. Dosing intervals based on active ingredient, i.e. moxidectin every 13 weeks, ivermectin every 8-10 weeks, pyrantel every 4-8 weeks or benzimidazole every 6-8 weeks. Remember it is important not to use wormers against which there is known resistance in horses. With resistance to benzimidazole3, pyrantel4 and ivermectin5 based wormers you may want to seek guidance from your vet prior to their use.

Additional treatments to be added if not covered as part of routine treatment. Dependent on active ingredient used for routine roundworm control.

Tapeworms: Treat for tapeworm in the autumn. Traditionally treatment involved a double-dose of a pyrantel-based wormer, however praziquantel-based wormers that specifically target tapeworm with a single dose are now available. Praziquantel-based wormers are typically presented in combination with other active ingredients, i.e. EQUEST PRAMOX containing moxidectin and praziquantel.

Encysted small redworm: Treat your horse in November against encysted small redworm larvae so as to reduce the burden of these life-threatening encysted larvae in your horse's gut wall. Treatment is with a single dose of a moxidectin-based wormer (i.e. EQUEST or EQUEST PRAMOX) or 5-day course of fenbendazole-based wormer. However, with widespread small redworm resistance to fenbendazole, and with evidence that this 5-day course may actually increase the selection pressure for resistance amongst small redworm6 the use of fenbendazole for the control of encysted small redworm larvae is not advisable where resistance is present7.

Autumn Worming Tips:

· Resting pasture from autumn to mid-summer is a good idea and will help to break the life cycle of most parasites. It is important to recognise, however, that resting pasture will not guarantee a worm free pasture as some parasites can survive on the pasture for many years.

· If a horse is prone to eating its bedding then wood shavings or paper should be used instead of hay in order to help reduce the risk of it ingesting parasites.

For further information on worming plus a free worming calendar, call the EQUEST/EQUITAPE literature hotline on 01489 774232 or
Email:equest-uk@fdah.com or visit www.wormingyourhorse.info