INTERBREED DIFFERENCES IN THE EFFICACY OF 1-PERCENT DELTAMETHRIN POUR-ON TO PROTECT SMALL LIVESTOCK AGAINST INFESTATION WITH IXODES RUBICUNDUS (ACARI, IXODIDAE)

Synthetic pyrethroid pour-on compounds have been developed for use on cattle but many are now also registered for the control of ectoparasit es on small ruminants. The breed of small livestock has been known to influence the efficacy of various pour-ons and we hypothesized that di fferences in the duration of protection afforded by a synthetic pyreth roid pour-on against ticks on small livestock, would be greatest betwe en hairy and woolly breeds, Angora goats with mohair, Dorper sheep wit h hairy wool, and Merino sheep with wool were treated with 1% m/v delt amethrin pour-on with an oil base at a dosage rate of 1 ml 5kg(-1) bod y mass, The duration of effective protection against Ixodes rubicundus , the Karoo paralysis tick, was determined under field conditions. Ang ora goats proved to be the highest risk group, but were afforded the l east protection. Efficacy never reached 100% in this group and within 3 weeks the goats were already at risk of paralysis. Dorper sheep were afforded above 90% protection for 3 weeks and 85% after 4 weeks, In t he case of the Merino sheep efficacy of protection remained above 90% up to 7 weeks post-treatment and was still 87% during Week 8, Differen ces in the amount of sebum and suint in the epidermis of the different breeds may be responsible for differences in the rate of spread and t he rate of dilution of the active compound in the epidermis.