Pay Special Attention To Worming Young Horses Says Zoetis

Zoetis Inc. today announced that whether breeding a Thoroughbred for a career on the track or a crossbreed leisure horse for a life as a hack, good worm control is essential to help produce healthy youngsters. Currently, information on best worming strategies for foals and yearlings remains largely anecdotal but Zoetis Vet, Dr Wendy Talbot has some suggestions to help guide you on the right course.

Foals and yearlings are usually more susceptible to worms than adults because they have had little chance to develop any tolerance. They are more vulnerable to parasite-related diseases and tend to have higher egg shedding, which increases the risk of infection. The main parasitic culprits in the UK for foals less than six months of age are large roundworms. In older foals and weanlings, small and large redworms, tapeworms (and pinworms) are the main considerations.1 Yearlings may also have a second wave of large roundworm infection at 8-10 months of age.2 Any control strategy will need to take into account the individual circumstances such as stocking density, pasture management and previous disease history.

Guidelines for parasite control in foals suggest treatments for roundworm at 2-3 months and 5-6 months of age. At weaning (approximately six months of age), it is advisable to perform a faecal worm egg count (FWEC) to determine if treatment for redworm is also needed. At 9 and 12 months of age treatment for redworms and encysted small redworm are advised.  A tapeworm test or treatment should be included with one of these doses.2,3

For yearlings, two methods have recently been proposed for worm control: the first involves using faecal worm egg counts (FWECs) at more frequent intervals than for adults to guide dosing for redworms in the grazing season. Ideally they should be conducted every 6-12 weeks depending on the worming product last used and individual circumstances.1 The second suggests three baseline treatments targeting redworms in spring, summer and late autumn, with FWECs in between to identify and treat any still shedding high numbers of eggs, up to a maximum of six treatments per year.2 Both strategies include a treatment for encysted small redworm combined with testing or treating for tapeworm in late autumn.

It’s important to discuss your worm control plan with your vet or SQP who will be able to devise the best strategy for your individual circumstances. Wendy has summarised some of the key points to consider:

  • Clean pasture is key to keeping foals and youngstock healthy.  Regular removal of droppings is crucial to a successful worm control plan.
  • All foals are considered to be susceptible and at risk of acquiring large roundworm infection. Some degree of anthelmintic intervention should be considered and in most circumstances administration at 2-3 months of age and again at 5-6 months of age is advisable.4
  • Older foals are primarily at risk of strongyle infection; macrocyclic lactone anthelmintics (moxidectin or ivermectin) have the highest expected efficacy.
  • Worm egg counts are likely to be higher in yearlings compared to adults and interpretation of them requires good knowledge of all the circumstances including management, clinical history, previous worm control and test results. Treatment of encysted small redworm is advised for all youngsters (> 6 months of age) in late autumn.1
  • Faecal worm egg counts are advisable in late winter/start of spring to identify high shedders. These horses may require treating again for encysted small redworm, particularly after a mild winter.1
  • New arrivals should be dosed with a wormer effective against all stages of small redworm, roundworm, tapeworm and bots and then quarantined for three days.1
  • A yearly faecal egg count reduction test is advised to check efficacy against strongyles and large roundworms for all class of drugs used on the premises.1

For further information on worming and many other aspects of horse care visit

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