Use a worm egg count to determine the need for worming. Adult horses with a worm egg count result over 200 epg (eggs per gram) should receive treatments no less than 8-10 weeks apart, when shown to be necessary. Foals should receive treatments no less than 6 weeks apart.
The only really effective way of controlling worms is to use a planned worming programme such as the free online SMART planner, combined with good pasture management. This includes removing droppings twice a week and not grazing too many horses together. Resting the pasture or rotational grazing is a worthwhile strategy, but only if the paddocks are left rested from autumn to mid-June the following year. The exception is large roundworms of foals, which can survive on the pastures for years.
With roundworm eggs, the cycle of infection begins when they are passed out in the droppings and develop into immature worms in the dung. These then climb up blades of damp grass and are eaten by the horse. With tapeworm, horses become infected when grazing or eating hay contaminated with immature tapeworms.
In a typical life cycle, immature worms (larvae) hatch from eggs in dung and then crawl up blades of grass near the dung and are eaten. Most immature worms develop into adults in the gut of the horse. Some species burrow through the gut wall into the blood and are then carried to other parts of the body. It is here, in areas such as the arteries, liver or lungs, where the immature stages of the worms can cause serious damage before making their way back to the gut to complete their development into adult worms. Eggs from adult worms are passed out in the dung to start the cycle of infection again.
Foals are particularly susceptible to worm infestations and should be routinely treated (together with their dams) from 6 weeks of age until they are around 18 months old, on the advice of your vet or SQP.
Foals can become infected with threadworms soon after birth via the mare's milk. This is one of a number of causes of diarrhoea in young foals. If threadworms are confirmed to be the cause, affected foals will need worming in the first few weeks of life with a wormer recommended for treatment of very young foals.
Large roundworms are also important and can be fatal in young growing foals up to
18 months of age. Check regularly for large roundworms using worm egg counts.
EQVALAN® is recommended for the treatment of both threadworms and large roundworms at the standard dose in foals under 4 months of age.
Small redworms can be present in huge numbers and usually account for at least 90% of the horse’s worm burden. It is not unusual for horses to be infected with as many as a million of these parasites. In the autumn, as it gets colder, an increasing number of immature worms hibernate in the gut wall in small cysts. At this stage, they are very resistant to worm treatment and can cause problems when they erupt out the gut wall. If tens of thousands all emerge at the same time, this causes massive damage leading to loss of condition, diarrhoea, colic and even death. Large redworms are also very damaging and potentially fatal but less common than small redworms. Severe tapeworm infection can cause colic and even death.
Yes, worms that affect horses do not generally affect sheep or cattle and vice versa, so, if you can, graze them together. This will help reduce the number of worms that your horses are exposed to and improve the pasture quality.