Foals are born free of parasites but get exposed to them within the first few days of life. Threadworm is the first possibility which can travel through mare’s milk to infect the foal and they are also likely to encounter ascarids, redworm and tapeworm as soon as they’re out in the pasture. Because of this and their immature immune systems we recommend proactively worming foals from four weeks old, every six to eight weeks.
With wormer resistance increasing it can be advisable to put a couple of worm egg counts into your programme during this time but we don’t often get samples to test from very young foals. But as this handsome chap, a Quarter Horse foal called Maverick, belongs to one of our team, we were of course straight in to take a peak in his poo. :)
At exactly four weeks old Maverick had his first worm egg count and we were really surprised to find a low count for redworm (50 e.p.g. Strongyle eggs). So despite his young age he had already ingested redworm larvae that had developed within his gut to become egg laying adults.
Now this result is particularly unexpected as small redworm are estimated to have a lifecycle of between five to six weeks. It shouldn’t even be possible for him to have a positive worm egg count at this time but here it is!
Perhaps the lifecycle of some species of small redworm is even faster than first thought. Maverick’s result is testimony to just how easily horses can become infected and how rapidly this parasite can begin to colonise in their gut. This tenacity is what makes small redworm such a threat to horse health and why a redworm problem in particular, can so quickly get out of hand.
Where did the redworm come from?
Although very young foals don’t graze or eat hard feed they are curious about exploring their environment and mimic grazing behaviour, mouthing at grass and licking and investigating with their muzzles.
At just a few days old Maverick was also observed enthusiastically attempting to eat his mum's fresh poo. This is a common behavior called coprophagia, which is from the Latin for "feces eating." It can take up to a year or more for foals to develop a healthy gut and so they eat poo to help populate their system with micro organisms to aid digestion.
It is also thought that as parasite eggs and larvae are likely to be ingested as part of this process, in the right environment this could help stimulate the foals' immune system and help to build a natural defence. In other words it’s not about eliminating exposure to parasites which is impossible, but rather managing a burden and stepping in before the level where it could cause disease.
Parasite infection could have come from both of the behaviours described above.
What to do about it?
Effective worming is a vital part of giving young horses a healthy start. We’d planned to worm Maverick at four weeks anyway and he was given a single dose of fenbendazole, a very safe wormer for youngsters. Since then we have continued to worm him every four - six weeks alternating between pyrantel and fenbendazole and will do so until he’s six months old. We’ve also taken a worm egg count before each treatment to keep an eye on what’s going on. Both subsequent worm egg counts have been <50 e.p.g no eggs seen in the sample which shows that the wormers have been effective.
For more info on parasite control in mares and foals read our guide here 👉 bit.ly/wormingyounghorses
Takeaway messages:
- Foals are especially vulnerable to parasite infection and benefit from proactive treatment up to six months of age
- The lifecycle of some small redworm species can be as short as four weeks
- Some strategic worm egg counting of foals is beneficial due to increasing wormer resistance