A comparison of persistent anthelmintic efficacy of topical formulations of doramectin, ivermectin, eprinomectin and moxidectin against naturally acquired nematode infections of beef calves.

Persistent anthelmintic efficacy of topical formulations (all at a dosage of 500 microg/kg) of doramectin (DOR), ivermectin (IVM), eprinomectin (EPR) and moxidectin (MOX), in comparison with untreated control cattle (CONT), was observed in stocker beef calves during a 112-day winter-spring grazing trial. Five groups of 15 calves per group were grazed on 15 separate 2 ha pastures following random assignment of animals to specific pastures and then to treatment groups. All of the 5 treatments were represented in each of the 15 pastures. All cattle were weighed on study Days 1, 0, 28, 56, 84, 111 and 112. Fecal samples for nematode egg counts were collected on Days 7, 0, at 7 day intervals through Day 56 and at 14 day intervals to Day 1 12. Pooled group fecal cultures for determining generic composition of nematode infections were prepared at 14 day intervals throughout the study. As based on fecal egg counts, anthelmintic activity of EPR and MOX was greater (p < 0.05) than values for IVM or CONT through Day 28. Activity of DOR was greater (p < 0.05) than that of IVM on Days 7 and 14 only. Although significance levels varied little among treated groups from Day 42 to the end of the study, egg counts and percent reduction values of EPR and MOX remained consistently lower numerically than egg counts and higher than reduction values respectively, of DOR and IVM through Day 70. From Day 70 on, IVM counts were numerically, but not significantly higher than values of CONT. Based on larval culture, Cooperia predominated from Day 0 through 28 and again from Days 70 to 98; Ostertagia was second in prevalence with highest percentages, which exceeded those of Cooperia, between Days 42 and 70. Bodyweights of all treated groups, with exception of IVM, were always significantly greater (p < 0.05) than weights of CONT. Weights of IVM were numerically greater, but not significantly greater than CONT only on Days 84 and 112. From Day 56 on, there were no significant differences between weights of DOR, EPR and MOX, however, numerical values for MOX were consistently higher than values for the other two. Final average total bodyweight gains were: 153.7 kg for MOX, 148.5 kg for EPR, 146.9 kg for DOR, 139.7 kg for IVM and 127.7 kg for CONT.

Evaluation of the therapeutic and protective efficacy of doramectin against psoroptic scabies in cattle.

Three studies were conducted to evaluate the therapeutic and protective efficacy of doramectin when given by injection at a dose of 200 micrograms/kg against induced Psoroptes otis infestations of cattle. The first study investigated therapeutic efficacy. Mite infestations were established on 15 test animals held in stanchions by transfer of material from infested donor calves. Test animals were then allotted on the basis of mite counts to a treatment group (10 animals) which received doramectin and a control group (5 animals) which received saline. Skin scrapings were collected for mite counts on the day before treatment and on days 7, 14, 21 and 28 after treatment. Efficacy assessed on the basis of the proportion of animals cured by day 28 was 100%. The second study was designed to determine the duration of protective efficacy. Forty-eight scabies-free heifers were allotted to a treated group of 32 which received doramectin, and a control group of 16 which remained untreated. These treatment groups were each divided into eight subgroups. Commencing on treatment day and continuing at weekly intervals for 7 weeks, a subgroup of animals from each treatment was placed in stanchions and challenged by transfer of material from infested donor calves. Skin scrapings for mite counts were collected 7 and 14 days later. Infestations were successfully established on all untreated control calves. Doramectin prevented the establishment of infestation for three weeks and significantly (P < 0.05) reduced infestation levels for an additional two weeks. The third study established the duration of residual protection conferred by doramectin and ivermectin under contact transmission. Ninety-six scabies-free heifers were divided into two equal treatment groups. Animals in one group received doramectin and animals in the other group received ivermectin at its recommended dose of 200 micrograms/kg by subcutaneous injection. Each treatment group was then divided into eight subgroups of six animals. Commencing on treatment day and continuing at weekly intervals for 7 weeks a subgroup of animals from each treatment was exposed to purposely infested seeder animals for one week. Three animals from each treatment subgroup were then placed in individual stanchions in which grooming was prevented and the other three were placed together in a pen where normal grooming behavior was permitted. Skin scrapings for mite counts were collected at weekly intervals for up to 4 weeks. Doramectin provided complete protection against infestation for five weeks compared to four weeks for ivermectin. These periods were not influenced by grooming behavior.

Systemic activity of nifluridide against sucking lice and the common scabies mite on cattle.

Psoroptes ovis [Hering] mites and sucking lice (Linognathus vituli Linnaeus) were eliminated from light to heavily infested calves with a single subcutaneous injection of nifluridide in five separate experiments. The compound was incorporated in a copolymer vehicle in a sesame oil suspension. In the first two experiments, mites were eliminated within 10 days following a 20 mg kg-1 injection. Eight out of 9 calves were cleared of mites within 7 days post injection of nifluridide at 4, 6 and 9 mg kg-1 in the third experiment. At the end of the 65 day trial, no live mites were isolated from any of the treated animals. In the last two experiments nifluridide eliminated sucking lice populations at all dosage levels. Complete control of the biting lice (Bovicola bovis) was not obtained. No toxic signs were observed in treated calves.