Treatment and prophylaxis of psoroptic mange (sheep scab) using an ivermectin intraruminal controlled-release bolus for sheep.

In an experiment to determine the therapeutic efficacy of an ivermectin intraruminal controlled-release (CR) bolus, 14 mixed breed sheep of one lot were infested with Psoroptes ovis and subsequently divided into two groups of seven. In one of these groups each sheep received one ivermectin CR bolus appropriate to its weight, the other group remained as an untreated control. All mites were eliminated from the group receiving the bolus while the control group remained infested, the disease progressed, and all but one sheep required treatment for psoroptic mange before the end of the experimental period. A second lot of 14 sheep, free from P. ovis, were divided equally into two groups to determine the prophylactic efficacy of the ivermectin CR bolus. In one group, each sheep was given an ivermectin CR bolus according to body weight and the sheep in the other group received no medication and served as untreated controls. Twenty-one days later two sheep infested with psoroptic mange were introduced into each of the groups. These donor sheep were removed 10 days later. The group treated with the ivermectin CR bolus remained mange-free and did not harbour any mites. All of the sheep in the control group developed psoroptic mange and required treatment to control the infestation at the end of the experimental period. Sheep that received the ivermectin CR bolus had greater mean weight gains than the control groups in these experiments. The ivermectin CR bolus releases a minimum dose of 20 microg ivermectin kg/day for 100 days: this prolonged activity should prove a valuable asset for the treatment and control of psoroptic mange in sheep.