Ivermectin Toxicity
By Dr Mackie Hobson BSc(Agric),BVSc

Tuesday, 18th April 2017

Anthelmitic use in Angora goats generally is advised (off label) at 1.5-2x the Sheep therapeutic dose as goats metabolise anthelmintics (doses) at a much faster rate than sheep. In sheep it takes about 11 days for ivermectin to drop below the detectable level in blood, whereas in goats this level is reached 4 to 5 days after administration.

On the odd occasion farmers have seen the side effects of an ivermectin (macrolytic lactone) overdose. This may occur due to a couple of errors:

  • Intramuscular injection given instead of a subcutaneous injection. This results in excessive blood levels.
  • Another frequent error is repeated injection of the same goat through misidentification.
  • Not knowing the weight of the Angora goat and giving the same (1,5-2x) dose of the heavier goats to even to the smallest goat.
  • The effect of feed on the blood levels of oral ivermectin doses. Ivermectin binds strongly to food particles in the stomach. So starved goats and fed goats will have different immediate blood levels of ivermectin. The faster the food leaves the rumen, the shorter and lower is the absorption.
  • As a general rule, young animals are more sensitive to overdosing, react stronger and prognosis is worse than for adult animals.

Toxicity symptoms:

  • Ataxia (uncoordinated movements)
  • Hypermetria (excessive or disproportionate movements)
  • Disorientation
  • Hyperesthesia (excessive reaction to tactile stimuli)
  • Tremors
  • Mydriasis (dilatation of the pupils)
  • Become recumbent
  • Depression
  • Blindness


  • There is no antidote for ivermectin poisoning.
  • Treatment consists in supportive treatment.
  • Most goats recover in a couple of days.


Which anthelmintics contain ivermectin (macrolytic lactones)?

See our website GROUP 1 and COMBINATIONS


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