A new horse can bring any number of infections into your yard – including worms. It’s up to you as his owner to think about your new horse’s welfare, the other horses on the yard and how to reduce the potential risks with worming. A new horse could bring high levels of worms with them, with the added issue that these may be worms that are resistant to one or more of the worming treatments currently available. This means they may be tougher to get rid of and they could cause ongoing problems for the entire yard!
Unless you have a very clear and trustworthy history of worming for your new horse, it is always best to err on the side of caution. Treating soon after arrival with a wormer that is licensed to control benzimidazole resistant worms and one that will kill all stages of worm in the horse is advisable in most situations – tapeworm should also be included for the same reasons. This will ensure that your new horse is as worm free as possible and reduces the risk of bringing resistant worms onto the yard. It also means that the horse can be quickly integrated into the yard’s worm management system – which is hopefully a balanced approach with pasture management and testing aligned with strategic treatments.
The other thing to consider is that it can be useful to have your new horse tested to assess their current worm burden before any treatment. A faecal worm egg count (FWEC) will give you an indication of the adult redworm and roundworm parasites in your horse by measuring the number of worm eggs in a dung sample, reported as eggs per gram (epg). With a new horse it may not change the decision as to whether to worm or not, but it does start to build a picture of the worm burden that they carry and how their worming regime can be best integrated onto the yard’s general worm management.
Keep them in
Viable eggs may continue to be passed in the faeces for around a couple of days after you have wormed your new horse so it’s important that you keep them off pasture for this period (~48hrs) to avoid the contamination of your grazing. Even if they are going to be out on their own, it is still worthwhile to keep them off the field as they will still shed worm eggs onto the pasture and may re-infect themselves when the worm larvae have matured.
Remember ongoing pasture management
Once your new horse has been integrated into your worming programme with the other horses on the yard, the importance of ongoing pasture management should never be under-estimated – it is inexorably linked to worm control strategy. Low stocking densities, the daily collection of droppings, the grazing of other stock such as sheep or cattle on the land and the rotation and resting of pasture will reduce contamination and the exposure of the horses to infective larvae. Clearly a good worm control strategy will also result in less pasture contamination.
In addition, an FWEC from your new horse 6-13 weeks post arrival (depending on the wormer used) will be a useful guide as to how they are coping initially with their new environment and the worm challenge. The other thing to remember is that a new horse will always change the dynamic in the yard, whether with field pecking order or worm control! The new horse may well shed more over the first few months and they may cause horses that have previously coped well on the yard, to pick up an increasing burden and need treating more frequently.