Refugia

What is refugia?

Horse parasite refugia is a population of worms that have not been exposed to anthelmintic treatments, such as dewormers. This can include worms within an untreated horse, encysted cyathostomes (redworm), and those parasite stages on the pasture. The goal of a refugia is to dilute the population of resistant worms and prevent them from becoming a significant proportion of the farm's worm population.

Here are some things to consider when managing parasite refugia:

• Seasonal environmental patterns - The development and survival of worm larvae is influenced by seasonal environmental patterns, such as temperature and rainfall. In regions with short periods of hot and dry or cold weather, or where there is regular rainfall, larvae can develop and survive year-round. In regions with prolonged periods of dry, very hot, or very cold weather, few larvae will develop or survive.

• Anthelmintic treatments - When refugia is low, it's important to keep anthelmintic (wormer) treatments to a minimum to reduce the selection for resistant worms. Only worm your horse when you need to.

• Leaving some horses untreated - Some horses are natural high shedders, meaning they shed a higher number of eggs onto the pasture. Leaving a few horses untreated can help reduce the development of resistance.

Reference: Information adapted from the World Association for the Advancement of Veterinary Parasitology (WAAVP) and the American Association of Equine Practitioners (AAEP) internal parasite control guidelines, including published research by Dr. Martin Nielsen on equine parasite refugia (aaep.org).