Field studies investigating anthelmintic resistance in young cattle on five farms in New Zealand.
OBJECTIVE
To investigate the efficacy of pour-on anthelmintics against field strains of parasitic nematodes in young cattle on five farms in New Zealand.


METHODS
Faecal nematode egg count (FEC) reduction (FECR) tests were carried out on five calf-rearing farms using pour-on formulations of levamisole, ivermectin, eprinomectin, and the simultaneous administration of levamisole and ivermectin. Faecal samples were collected per rectum before treatment and about 7, 14, 21 and 28 days after treatment, for FEC and faecal nematode larval culture.


RESULTS
Resistance (i.e. <95% reduction in FEC) of Cooperia oncophora to ivermectin and eprinomectin was identified on all five farms. There was limited evidence of possible emerging resistance in Ostertagia spp to ivermectin but not eprinomectin, in short-tailed larvae of Cooperia spp to ivermectin and eprinomectin, and in Trichostrongylus spp to ivermectin, eprinomectin and levamisole used separately. Levamisole was effective against C. oncophora, but had variable efficacy against Ostertagia spp in the calves in this study. Simultaneous treatment with levamisole and ivermectin pour-on formulations were effective against all genera on all farms.


CONCLUSIONS
To effectively manage roundworm parasites in their calves farmers need to be aware of the resistance status of the parasites on their farms. Levamisole is likely to be an effective anthelmintic on most farms at times of the year when the impact of Ostertagia spp is not high. Simultaneous administration of levamisole and ivermectin pour-on anthelmintics to cattle is likely to control both ML-resistant C. oncophora and stages of Ostertagia spp that are not controlled by levamisole alone.
Mason
P C
PC
Mason Consulting, 317 Dunns Crossing Road, RD5, Christchurch 7675, New Zealand. masonp@earthlight.co.nz
McKay
C H
CH
D000818:Animals; D000871:Anthelmintics / Q000494:pharmacology* / Q000627:therapeutic use; D002417:Cattle; D002418:Cattle Diseases / Q000188:drug therapy* / Q000453:epidemiology; D004351:Drug Resistance; D004359:Drug Therapy, Combination; D005243:Feces / Q000469:parasitology; D005260:Female; D006374:Helminthiasis, Animal / Q000188:drug therapy* / Q000453:epidemiology; D007559:Ivermectin / Q000031:analogs & derivatives / Q000494:pharmacology / Q000627:therapeutic use; D007978:Levamisole / Q000494:pharmacology / Q000627:therapeutic use; D008297:Male; D009348:Nematoda / Q000187:drug effects; D009349:Nematode Infections / Q000188:drug therapy / Q000453:epidemiology / Q000469:parasitology / Q000662:veterinary; D009520:New Zealand / Q000453:epidemiology; D010028:Ostertagia / Q000187:drug effects; D010029:Ostertagiasis / Q000188:drug therapy / Q000453:epidemiology / Q000469:parasitology / Q000662:veterinary; D010270:Parasite Egg Count / Q000662:veterinary; D021261:Parasitic Sensitivity Tests / Q000662:veterinary; D013997:Time Factors; D016896:Treatment Outcome
D000871:Anthelmintics; D007978:Levamisole; D007559:Ivermectin; C101434:eprinomectin