Parasite control is an important part of mare and foal care. | Photo: Photos.com

Times are changing when it comes to equine parasite control: Anthelmintic-resistant parasites have prompted new, more targeted deworming recommendations. Two important classes of horses that fall under this deworming protocol are broodmares and foals. At the 2013 Society for Theriogenology Conference, held Aug. 7-10 in Louisville, Ky., Wendy Vaala, VMD, Dipl. ACVIM, presented a lecture on current parasite control recommendations for mares and foals.

Vaala, the senior equine technical services veterinarian at Merck Animal Health, began by reviewing the current challenges of effective deworming, specifically anthelmintic resistance. She described anthelmintic resistance as “the ability of worms to survive treatments that are considered effective against that species and/or stage of infections.” Essentially, previously reliable treatments no longer eliminate worms from a horse’s body successfully.

“In order for anthelmintic resistance to develop on a farm, the gene mutations that confer drug resistance must already be present within the resident worm population,” she explained. Once that occurs, frequent drug use allows resistant parasites to survive and multiply. “The history of drug use on a farm plays a major role in how quickly resistance develops and to which drugs