A field trial to determine the effect of fly control using permethrin on milk yields in dairy cattle in the UK.

Permethrin, applied by knapsack sprayer or spray arch, was used to control flies on cattle in two dairy herds in the United Kingdom. The spray washes were applied at nominal rates of 0.5 litre of 0.1 per cent permethrin per animal and 1.0 litre of 0.05 per cent permethrin per animal respectively. The individual milk yields of two groups of cows were recorded before and after treatment. In both cases there was a significant increase in milk yield after treatment. The mean yield per cow per day during the trial period rose by 0.8 kg in one group and by 1.0 kg in the other group, after treatment. Assessments were made throughout the trial of the level of infestation of Stomoxys calcitrans, Haematobia irritans and non-biting flies.