Comparison of an amitraz-impregnated collar with topical administration of fipronil for prevention of experimental and natural infestations by the brown dog tick (Rhipicephalus sanguineus).

OBJECTIVE: To compare the efficacies of amitraz and fipronil for prevention of experimental and natural infestations of Rhipicephalus sanguineus. DESIGN: Prospective study. ANIMALS: 30 dogs. PROCEDURE: In 3 trials, dogs were allocated to 3 groups of 10 each. In trial 1, dogs were experimentally infested on day--1, and on day 0 were fitted with an amitraz-impregnated collar, treated topically with fipronil, or not treated. Ticks were counted daily until day 7, when viability of ticks and their progeny was determined. In trial 2, dogs were treated on day 0 and experimentally infested on days 7, 8, 10, and 13. Ticks were counted on days 8, 10, 13, and 18, and viability of ticks and their progeny was determined on day 18. In trial 3, dogs were exposed weekly to a tick-infested environment from day--3 to day 70. Dogs were treated on day 0, and ticks were counted and removed weekly from day 3 to day 77. RESULTS: Fipronil and amitraz were acaricidal and inhibited attachment and feeding. Amitraz had a significantly greater effect than fipronil on numbers of live, feeding ticks, egg hatchability, and larval viability, indicating partial ability to interrupt the tick life cycle. In field conditions, amitraz remained effective over the entire observation period. CLINICAL IMPLICATIONS: Amitraz had stronger and more sustained effects against tick infestation than fipronil.

Effect of three sustained-release devices on parasitic bronchitis in first year calves.

The effect of three intraruminal sustained-release devices (SRD) against Dictyocaulus viviparus infection was tested in five groups of six calves. Group 1 served as untreated controls, and groups 2, 3 and 4 were dosed with a levamisole SRD, a fenbendazole SRD, and an ivermectin SRD, respectively. Group 5 was vaccinated against lungworm and received a levamisole SRD. The calves were turned out on May 28 and the devices given seven days later. All the calves received trickle infections with a total of 200 lungworm larvae between 9 and 34 days after turnout. They were housed on October 28, challenged with 5000 lungworm larvae and slaughtered three weeks later. No clinical signs of parasitic bronchitis were observed during the study. The treated groups gained significantly more weight (P < 0.05) than the controls, but did not differ among themselves. Larvae were first detected in the faeces of the control group between 25 and 32 days after the first infection, and had a group mean of 21 larvae per gram (lpg) after 60 to 80 days, after which the lpg gradually decreased. In group 2, larvae were detected near the end of the grazing season and never exceeded a group mean of 1.5 lpg. In group 3, a very low larval output was observed after housing (group mean 0.1 lpg). Groups 4 and 5 never became patent. The results of an ELISA followed the pattern of larval output; optical densities above the cut-off value were recorded in groups 1, 2 and 3. On the basis of worm recoveries after challenge, group 1 was immune. Group 4 had significantly more lungworms than group 2. There were no significant differences in worm numbers between groups 2, 3 and 5, but the worms in group 5 were retarded in growth (P < 0.05).

Combined effect of ampicillin, colistin and dexamethasone administered intramuscularly to dairy cows on the clinico-pathological course of E. coli-endotoxin mastitis.

The effects of a single intramuscular injection of a drug product containing ampicillin, colistin and dexamethasone, as a suspension in a diester of propylene glycol of medium-chain fatty acids, on the clinico-pathological course of experimental Escherichia coli-endotoxin mastitis was examined in 30 dairy cows. Cows were divided into five groups, six cows per group, and 24 of them were infused with E. coli endotoxin into two quarters of their udders. The drug product was injected at 25,000 IU colistin sulphate, 10.0 mg ampicillin anhydrate and 0.025 mg dexamethasone acetate.kg-1 body weight as follows: Group 2 cows, immediately post-endotoxin infusion (PEI); Group 3 cows, 2 h PEI and, Group 4 cows, 4 h PEI. Group 1 cows were not treated with the product and served as a positive (endotoxin only) control while Group 5 cows were not challenged with endotoxin and were not treated with the product. A clinical mastitis score (CMS) was developed to quantitatively assess the degree of inflammation. Blood biochemistry and hematological parameters were used to monitor the immediate effects of treatment on several conventional inflammatory markers. Milk somatic cell counts (MSCC), milk electrical conductivity and daily milk production were among the parameters used to monitor systemic and local inflammatory reactions. Administration of the drug product immediately PEI and 2 h PEI clearly nullified some of the most severe early systemic reactions to inflammation but the effect of therapy on the local inflammatory markers was not as obvious. Notewhorthy, however, were the effects of the treatment on reducing the duration of elevated quarter MSCC and the increase in the speed of return to pre-endotoxin challenge daily milk production levels.