Persistence of the activity of topical ivermectin against biting lice (Bovicola bovis).

To assess the persistence of the activity of topical ivermectin against a natural challenge with biting lice (Bovicola bovis), 90 mixed-breed cattle that had been treated to remove lice, were blocked by bodyweight within sex and randomly allocated to three treatments: untreated control, doramectin at 200 micrograms/kg by subcutaneous injection, and ivermectin at 500 micrograms/kg by topical application. Forty-five pens were blocked into three groups of 15, and the blocks of pens were randomly allocated to three 14-day challenge periods starting 21, 28 and 35 days after treatment. There were five pens per treatment for each challenge period, and one B bovis-infested donor calf was introduced into each pen containing two principal calves at the start of the challenge period for that block of pens. The calves were examined thoroughly for B bovis seven, 14 and 21 days after the introduction of the donors. There were no significant differences between the control and doramectin groups for the numbers of animals infested, or the geometric mean louse counts at the final examination for any of the challenge periods. At the final examination for each challenge period, the louse counts of the cattle treated with topical ivermectin were all zero, and significantly (P < 0.05) fewer cattle treated with topical ivermectin were infested than either the controls or cattle treated with doramectin.

Efeito persistente de ivermectin injetável contra Dermatobia hominis / Persistent effect of injectable ivermectin against Dermatobia hominis

O presente estudo foi desenvolvido com o objetivo de determinar, sob condiçöes a campo, o efeito persistente do ivermectin injetável contra Dermatobia hominis nos bovinos, comparado com um programa de tratamento tradicional para esse parasita

Effect of antiparasitic treatment in beef replacement heifers.

Two studies were conducted in western Canada to evaluate the impact of antiparasitic treatment on weight gain and reproductive performance in beef replacement heifers from weaning to first breeding. Treatment of heifers at weaning with ivermectin increased the rate of weight gain in comparison to treatment with fenthion. The feed efficiency of ivermectin-treated animals was also significantly better than those treated with fenthion. Increased weight was associated with an increased number of animals in estrus at the end of the feeding period for heifers receiving ivermectin. We concluded that treatment with ivermectin improved feed efficiency and weight gain in heifers from weaning to breeding. In turn, this weight gain appeared to be associated with an increased number of heifers in estrus.

Comparison of ivermectin, oxibendazole, and pyrantel pamoate in suppressing fecal egg output in horses.

Thirty resident horses at a boarding stable in Alberta were used to evaluate the relative efficacies of ivermectin, oxibendazole, and pyrantel pamoate in reducing fecal egg output in adult horses under routine management conditions during spring and early summer, and to more clearly define the duration of suppression of fecal egg production following anthelmintic treatment. Horses were blocked according to pretreatment egg counts and randomly assigned to one of three treatments: pyrantel pamoate at 6.6 mg/kg body weight; oxibendazole at 10 mg/kg body weight; or ivermectin at 200 mug/kg body weight. All treatments were administered orally as a paste on day 0.Fecal samples were collected for examination by the modified Wisconsin procedure before treatment, and then at 4-11 day intervals up to day 72.Very few if any strongyle eggs were found in the feces of any horses up to day 35. On days 42, 50 and 57, the geometric mean egg count for the ivermectin group was significantly (p<0.05) lower than that for the oxibendazole or pyrantel pamoate groups. Based on a survival curve analysis of the data, the mean number of days for recurrence of eggs in the feces was significantly longer for the ivermectin group than for the oxibendazole and pyrantel pamoate groups.Under conditions encountered in this study, the posttreatment interval to resumption of fecal egg out-put in horses treated with ivermectin was eight to nine weeks, compared with five to six weeks for horses treated with oxibendazole or pyrantel pamoate.

Comparative cost-effectiveness of ivermectin versus topical organophosphate in feedlot calves.

A study was conducted in a commercial feedlot in western Canada to evaluate the impact of treatment with ivermectin versus a topical organophosphate on growth rate and feed efficiency in calves entering a feedlot at an average 275 kg liveweight.A total of 9527 head of cattle was used. Variables measured included average daily gain, average days occupation, and feed conversion.Ivermectin treated animals gained an average 0.08 kg per day more than those treated with topical organophosphate. In addition, they required an average 0.23 kg less feed/kg gain. Based on an average 227 kg of gain, this would result in 11 fewer days occupation and 52.3 kg less feed for ivermectin treated animals. This equaled a net benefit of $7.04 per head over treatment costs for ivermectin treatment versus topical organophosphate.

Critical test and safety evaluations of an oral paste preparation of mebendazole and trichlorfon in horses.

Critical tests were done on 24 naturally parasitized horses to compare the antiparasitic activity of an oral paste preparation of mebendazole and trichlorfon with that of the marketed powder formulation. Each formulation was administered at the recommended dosages of 8.8 mg of mebendazole and 40 mg of trichlorfon/kg of body weight. Efficacy of the paste formulation ranged from 97.7% to 100% against 2nd- and 3rd-stage Gasterophilus spp, adult Strongylus vulgaris, S edentatus, Parascaris equorum, small strongyles; and larval and adult forms of Oxyuris equi. Adverse effects were generally limited to slight softening of the feces. Mild and transient restlessness or sweating were also observed in 2 of 12 horses treated with the paste formulation. The toxic effects of the paste, administered at 2.2 times the therapeutic dose, were examined in 6 horses and compared with the effects of a nonmedicated paste, administered in similar volumes to 6 other horses. Drug-related changes were not detected in clinical chemical analyses, hematologic values, or liver function tests. Transient clinical signs of organophosphate toxicosis (primarily the passage of loose feces) and prolonged inhibition of erythrocyte cholinesterase activity were evident within 1 hour after drug treatment. These effects were similar to those reported for the 2.2 X dose of marketed powder formulation.

Seasonal comparisons of anthelmintic activity of levamisole pour-on in cattle in the USA.

Anthelmintic activity of a pour-on formulation of levamisole, applied during warm weather (16 degrees to 36 degrees C) at 10 mg/kg bodyweight, was evaluated in groups of naturally parasitised calves. This activity was compared to that obtained in similar groups of calves treated in the winter (-4 degrees to +7 degrees C). Controlled efficacy of the pour-on formulation was determined for each season by comparing mean worm burdens in treated calves sacrificed seven to nine days after treatment to non-treated controls. In these trials, burdens of Bunostomum phlebotomum, Cooperia species, Haemonchus placei, Nematodirus species, Oesophagostomum radiatum, Ostertagia ostertagi and Trichostrongylus axei in treated calves were reduced by 83.3 to 100 per cent in the summer and 89.2 to 100 per cent in the winter. Field investigations at nine locations across the USA compared changes in faecal egg counts for cattle treated and evaluated during warm summer months (27 degrees to 36 degrees C) to those treated during cold winter months (-18 degrees to +10 degrees C). Overall, faecal egg counts were reduced by 90.2 per cent in the summer trials and 94.0 per cent in the winter trials. The results of these trials indicate that there is no seasonal variation in the anthelmintic activity of this pour-on formulation of levamisole.

Activity of closantel against experimentally induced Fascioloides magna infection in sheep.

The efficacy of closantel against experimentally induced Fascioloides magna infection in sheep was studied. In each of 3 experiments, closantel was administered 8 weeks after the sheep were given (oral inoculation) 100 metacercariae of F magna. In the 1st experiment, closantel was given orally to 5 groups of 6 sheep each at dosages of 0 (nontreated control), 5, 7.5, 10, and 15 mg/kg of body weight. In the 2nd and 3rd experiments, groups of 10 or 12 sheep were treated to confirm the efficacy of the previously determined optimal dosage of 15 mg/kg. An additional group of sheep (n = 10) was used in the 3rd experiment to evaluate the efficacy of closantel given IM at a dosage of 7.5 mg/kg. Closantel given orally at a dosage level of 15 mg/kg was highly effective (94.6% to 97.7%) in reducing F magna burdens. Also, pathologic scores associated with the F magna infection were reduced by 81.3% to 92.6% in sheep given this dosage of closantel. Efficacy of the IM administered dosage of 7.5 mg of drug/kg was equivalent to that of the 15 mg/kg oral dosage. Other than mild, transient lameness of the limbs which were injected with the drug (group 10), side effects were not observed.

Controlled and clinical evaluations of the anthelmintic activity of a levamisole pour-on formulation against gastrointestinal nematodes in cattle.

Beef-type calves (n = 107) with naturally occurring helminth infections were used in a series of 3 controlled experiments to study the anthelmintic activity of a new pour-on formulation of levamisole. In the 1st experiment, the efficacy of a single treatment of levamisole pour-on at a rate of 10 mg/kg of body weight was determined, using a placebo pour-on in a similar volume as a control. In the 2nd experiment, calves were treated with levamisole pour-on at doses 0 (nontreated control), 7.5, 10, or 12.5 mg/kg of body weight. In the 3rd experiment, the anthelmintic efficacy of the optimal dose of levamisole pour-on (10 mg/kg of body weight) was compared with that of injectable levamisole at the recommended rate (6 mg/kg of body weight). In all 3 studies, levamisole pour-on, at a dosage of 10 mg/kg of body weight, was efficacious (90% to 100%) against the adult forms of Trichostrongylus axei, Haemonchus placei, Ostertagia ostertagi, Cooperia spp, Oesophagostomum radiatum, Nematodirus spp, and Bunostomum phlebotomum. Efficacy was moderate to good against Capillaria bovis, and poor or inconsistent against Strongyloides papillosus and Trichuris ovis. Clinical tests of anthelmintic efficacy and local tolerance of levamisole pour-on were conducted in 371 beef and dairy cattle in Mexico. Fecal egg counts were consistently reduced 2 weeks after a single application of levamisole pour-on at a dosage of 10 mg/kg of body weight. Local reactions were limited to various degrees of dry hair coat for up to 2 weeks at the application site. Hair loss or skin abnormalities were not observed in any of the treated cattle.

Activity of flubendazole against developing stages of Dirofilaria immitis in dogs.

A formulation of flubendazole was studied to determine the activity against developing stages of Dirofilaria immitis in artificially infected pups. Flubendazole suspension was administered subcutaneously at a dose rate of 50 mg/kg of body weight once a day for 1, 3, or 5 consecutive days at various times during the experimental period. The pups were necropsied 6 months after the experimental infection, and the heart and pulmonary arteries were examined for adult worms. Optimal activity was obtained when flubendazole suspension was administered subcutaneously for 5 consecutive days, either 1 or 2 months after infection. The formation of encapsulated deposits, containing white viscous fluid, was observed at the injection sites of all treated pups.