STRONGYLE CONTROL AFTER MULTIYEAR USE OF IVERMECTIN IN HORSES ON A FARM IN CENTRAL KENTUCKY

Counts of strongyle eggs per gram of feces (epg) were determined biwee kly for an 8-wk period in 1991 and 1992 for 83 thoroughbred horse mare s (N = 21/yr) and yearlings (N = 20-21/yr) on a farm in central Kentuc ky. Historically, horses on this farm have been on a regular deworming program for nearly 5 decades. Ivermectin has been used approximately every 8 wk since 1983 when it was first marketed. There was occasional usage of pyrantel pamoate between routine ivermectin treatments. For the 2 evaluation periods, strongyle epg counts for mares were all nega tive and for yearlings were all negative except pretreatment for 1 yea rling (epg = 10) in 1991 and 3 yearlings (epg = 10, 10, and 30) in 199 2.