Foals and young horses (upto 18-24 months of age) are more susceptible to picking up worms as well as more vulnerable to diseases caused by worms, so control programs for youngstock need to be more rigorous. The commonest and most important worms that we need to control in youngstock are the ascarids (roundworms) and also the large and small redworms. Strongyloides (thread worms) occasionally cause diarrhoea in young foals, but this is rare. Small redworm eggs eaten by grazing youngstock can cause severe disease the following spring after the larvae ‘hibernating’ in the wall of the intestines over the winter, then 'erupt' all at once.
The aims of an effective worm control strategy for horses of any age or type are:
- To minimise the contamination of pasture by worm eggs (redworm eggs are passed in the droppings and contaminate the pasture; larvae develop on the grass and are then eaten and infect horses that are grazing).
- To keep the worm burden in an individual horse low enough to prevent disease.
There are two main components to an equine parasitic worm control programme:
1. Pasture management
2. Drug treatments ('dewormers' or 'anthelmintics')
1. PASTURE MANAGEMENT:
- CLEAN PASTURES: Foals should have the 'cleanest' (i.e. least heavily grazed) pasture – ideally pasture that has not been grazed by horses in the last 12 months
- STOCKING DENSITY: Horse numbers per acre should be kept low to prevent overgrazing and to reduce contamination by worm eggs. One adult horse for one or one and a half acres acre is an appropriate rule of thumb for minimum stocking density.
- POO PICKING: Pick up and dispose of dung more regularly than for adult horses (ideally every other day for youngstock). Do not spread this onto fields grazed by horses, as it simply spreads the worms around the fields. Instead, compost it away from grazed pasture and water courses.
- ROTATE PASTURES: If possible, rotate pastures to give recently grazed pasture time to ‘rest’ and ideally avoid grazing pasture grazed by foals the previous year
2. DRUG TREATMENTS ('Worming'):
As with adult horses, overuse of dewormers in foals and broodmares has caused some worms to become resistant to some equine dewormers, for example, many ascarid worms are resistant to ivermectin wormers. In mature horses, targeted treatment is used to decide which horses need worming; youngstock are more vulnerable and should be wormed regularly BUT the type of wormer should be chosen carefully to minimise resistance.
The following information is a general guide to worming youngstock (less than 18 months old) and broodmares, but in certain cases we may advise a slightly different approach, so please discuss your specific requirements with one of our vets or SQPs.
Broodmares:
- Until the 10th month of pregnancy the mare can follow the same worm control program as other adult horses.
- A faecal egg count should be performed within the last month of pregnancy and the mare should be treated, only if required. The faecal egg count should be repeated around 3-4 weeks after foaling.
Youngstock:
PLEASE ENSURE ALL FOALS RECEIVE WORMERS APPROPRIATE FOR THEIR AGE - ALWAYS CHECK THE INSTRUCTIONS BEFORE ADMINISTERING OR CONTACT BELL EQUINE ON 01622 813700
- Foals should be wormed regularly until they are 18 months old, regardless of any worm egg counts.
- The first treatment should be given at 2 -3 months of age using a benzimidazole (e.g. Panacur®) to treat ascarids (regardless of FEC results).
- Subsequently (after 4 months of age), the foal should be wormed according to the type of worms seen in routine faecal worm egg counts performed every eight weeks e.g. fenbendazole to treat ascarids; pyrantel, ivermectin or moxidectin to treat cyathostomes (moxidectin should not be used on foals less than 4 months of age).
- After weaning, youngstock should be treated at 3-4 month intervals until they are 18 months old. Recently weaned foals and yearlings are more likely to be high egg shedders, so routine monitoring (ideally every 3 months) of faecal egg shedding is paramount. Faecal worm egg counts can be used to identify the predominant type of worms (i.e. ascarids or small redworm) that the foal has - and this can help to determine the most appropriate class of wormer to use. In most cases, ascarid egg excretion peaks at 4-5 months of age then wanes.
- In the UK, many foals will be weaned in the autumn / ealry winter when a cyathostomin larvicidal treatment (i.e. moxidectin) should be considered. There can be a second wave of ascarid infection in some yearlings and FWEC should inform on the presence of this species.
- A product effective against tapeworm (moxidectin and praziquantal - Equest Pramox®) should be included at least once yearly provided the foal is older than 6 and a half months.
- From 18 months of age youngstock can follow a mature horse worming program assuming appropriate pasture management is followed. For yards with a history of worming problems, please speak to one of our vets or SQPs.