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Crossover of Ivermectin-
resistant Ostertagia from
goats to sheep -
Experiment 1
Ivermectin resistance diagnosed on
Massey research farm in 1989
Used other drenches until 1995
reused ivermectin in goats and sheep
to:
see how long it would take to re-
emerge?
see if it emerges in goats and
sheep at the same speed?
IVM resistance in Ostertagia
circumcincta rapidly re-emerged in
the goats but was never
convincingly diagnosed in the sheep