Pasture Management for Parasite Control

Testing alone won’t control parasites. Pasture and grazing management matters. 

None of us want to end up in the situation where untreatable parasite burdens mean we can no longer keep horses on our land, but wormer resistance raises this as a very real possibility.

Good pasture management and animal husbandry techniques, that breaks the lifecycle of the worms is beneficial in reducing the parasite threat to horses and reduce your reliance on chemicals to control your horse’s worm burden. This protects your grazing environment and prolongs the life of worming drugs for all horse owners.

Worm larvae passed in droppings hatch and become mobile within seven days at which point they leave the dung piles to re-infect the pasture. The milder and wetter the weather the further and faster the larvae can travel. Collecting droppings twice a week, even through winter is a sound investment in your worm control programme and there are other good pasture management practices that will help reduce the parasite risk on grazing lands:

Every Day Tips

• Quarantine procedures are not just for viral and bacterial infections. Keep new horses separate until tested and treated accordingly to avoid them bringing unwanted passengers onto your grazing!
• Poo pick regularly to remove droppings from fields and tracks at least twice a week to remove parasite eggs before they hatch - this breaks the lifecycle mechanically without relying on chemicals. Research shows that regular poo picking is as effective as giving a wormer.
• If your paddock or track management allows it, try to leave some fresh dung piles (up to 48hrs)  to help dung beetles do their bit too!
• Place muckheaps at least three metres from adjacent grazing land as motile larvae can travel this far from droppings to re-infect grazing.
• Avoid overstocking and over grazing paddocks as this increases the risk of worm exposure.
• Resting for at least 3 months - up to 12 months if you can, and rotating grazing paddocks allows worm larvae present to die off before they can find their way back into a horse. This helps to minimise the infection potential of your grazing.  
• Cross graze pasture with other species eg. Sheep. Worms are generally species specific and die off in the wrong host.
• Harrowing is not an effective method of parasite control in the UK and not recommended because of our climate. Even on hot days there is often a morning dew that prevents the desiccation of droppings necessary for this system to be employed effectively. Harrowing should be done during a spell of very hot, dry bright weather and within a system that includes resting and rotating grazing land.

After giving a chemical worming treatment 

• Don’t worm and move; after worming ensure horses stay on the same pasture for a few days to help slow down resistance.
• Keep horses stabled or contain them to a smaller grazing area after treatment so that they can be closely managed. Wormer excretion, that's the metabolites from the worming chemical that are passed out in the dung, peak around 24-48hrs after being given, dependent on digestive transit. If worming for tapeworm, it's also the time when packets of eggs will be excreted in the dung. 
• Where treatment is necessary, minimise the horse’s time on the pasture for up to 10 days and poo pick at least daily during this time. If you can only stable for a short time, advice is to keep horses in the day following worming. It may also help to restrict treated horses to a smaller paddock for 10 days to aid dung collection.
• Reduce environmental contamination by removing dung and placing it in a separate muckheap where it can be carefully composted to break down these components.
• It’s estimated that between 80 to 98% of an oral dose of ivermectin passes straight through the horse and is excreted in the dung without being metabolised by the body. Once in the environment it’s also one of the most resilient chemicals, persisting at high concentrations in faeces for many weeks.
• Of our five licenced wormers for horses, ivermectin is the most toxic to dung beetles and moxidectin moderately toxic while pyrantel, fenbendazole and praziquantel are significantly less poisonous.
• Be especially careful when using Ivermectin which is toxic to dogs and particularly is not well tolerated by Collies, Old English Sheep Dogs and their related breeds and crosses.
• Target wormers to only the horses that need it, leaving some untreated dung for dung beetles.
• If possible worm in late autumn/winter when dung beetles are less active.