Control of parasitic infection with ivermectin long-acting injection (IVOMEC® GOLD) and production benefit in first-season grazing cattle facing a high-level larval challenge in Germany.

Gastrointestinal and pulmonary nematode infections are affecting the health and productivity of grazing cattle worldwide. To evaluate the effects of a single treatment with ivermectin long-acting injection (IVM LAI; IVOMEC® GOLD, Merial; 3.15 % ivermectin w/v) in first-grazing season cattle, two studies were conducted under continued stocking conditions for 84 or 100 days in Bavaria, Germany. Each study involved 68 naturally infected, approximately 4- to 6-month-old Brown Swiss bull calves. Animals were blocked based on pretreatment body weights. Within each block of four animals, animals were randomly assigned to treatments: one to saline (control) and three to IVM LAI. Treatments were injected at 1 mL/50 kg body weight subcutaneously in front of the shoulder. Animals in both studies were managed as one herd each grazing together. Cattle were weighed and fecal samples were collected pretreatment and at intervals thereafter for determination of weight gain and treatment efficacy, respectively. Fecal examination including composite fecal culture indicated the presence of nematodes of the genera Cooperia (dominating), Haemonchus, Nematodirus, Ostertagia, Strongyloides, Trichostrongylus, Trichuris, and Dictyocaulus, and Moniezia cestodes in the cattle. Following treatment, IVM LAI-treated cattle did not shed any Dictyocaulus larvae for 84 days while controls continued to pass larvae. Compared to the controls, IVM LAI-treated cattle had significantly (p < 0.01) lower strongylid egg counts at each occasion. Percentage reductions were ≥94 % up to 70 days after treatment and were ≥83.9 and 58.9 % at 84 and 100 days. Over the 84- or 100-day study periods, IVM LAI-treated cattle gained significantly more weight than the controls: 22.7 and 12.4 kg, respectively. The two studies demonstrated a high efficacy of IVM LAI against gastrointestinal and pulmonary nematode infections under field conditions in Germany which was associated with significant benefit as to weight gain.