Evaluation of efficacy and benefit of ivermectin with clorsulon and long-acting moxidectin in replacement beef heifers
Keywords:heifers, ivermectin, moxidectin, parasites, animal parasitic nematodes, beef cattle, calves, clorsulon, drug therapy, helminth ova, helminthoses, helminths, infections, liveweight gain, multiple drug therapy, nematode infections, parasitoses, potency
A two-year study was conducted to assess the effects of ivermectin (with clorsulon) and long-acting moxidectin on the development of replacement beef heifers carrying naturally occurring parasite infections. Replacement beef heifers (n=105) were obtained at weaning and co-grazed on permanent pastures throughout the 686-day study. Study heifers were treated with ivermectin and clorsulon (IVCL), long-acting moxidectin (LMXD), or left untreated (CON). Treatments were administered on days 0 and 149. Compared to CON, heifer body weights were greater (P<0.05) for LMXD and IVCL-treated animals on days 175, 238, 287, 369, and 433. Average daily gains were greater (P<0.01) for LMXD and IVCL-treated heifers compared to CON heifers from days 0 to 433. Fecal strongyle egg counts were lower (P<0.01) for LMXD-treated heifers on days 14, 64, 149, 169, 238, and 287 compared to the IVCL and CON groups. Fecal egg counts for the IVCL group were lower (P<0.01) than those in the CON group on days 14 and 169, the samplings subsequent to animal treatments. Weight gain of calves born to the study heifers was greatest for calves born to LMXD-treated heifers, intermediate for calves born to IVCL-treated heifers, and lowest for calves born to CON heifers.