Resistance by Haemonchus contortus to ivermectin in angora goats
Craig, T.M.; Miller, D.K.
Veterinary Record 126(23): 580
1990
ISSN/ISBN: 0042-4900 PMID: 2368307 Document Number: 358871
For a 5-year period an Angora goat flock in east Texas, USA consisting of about 600 adult animals had been treated at approximately 3 week intervals during the spring and summer with ivermectin in polypropylene glycol given orally at a dose rate of about 0.2 mg/kg to the adults and 0.3 mg/kg to the kids. There had been occasional switching to treatment with benzimidazoles. When this procedure did not prevent the development of clinical signs of parasitic gastroenteritis, a trial was run with groups of 15 randomly selected adult goats and yearlings comparing the nematode egg reducing abilities of ivermectin orally (IVO PO) and ivermectin subcutaneously (IVO SQ) both at 0.2 mg/kg with oxfendazole orally (5 mg/kg) and levamisole orally (7.9 mg/kg). The remaining goats in the herd were treated with 0.4 mg/kg. Goats in the control group showed an increase in the number of eggs per gram of faeces (epg). Comparison of the geometric mean percentage reduction in epg showed that H. contortus was resistant to IVO PO, IVO SQ and oxfendazole but not to levamisole. Results of a simplified faecal egg count reduction test on the group treated with double the ivermectin dose confirmed that resistance to ivermectin had developed.