Abstract
Flies have been incriminated as vectors of summer mastitis. The efficacy of cypermethrin, formulated as a spray, in the control of the disease was investigated in two experiments. In this study, 1033 dry cows and 454 heifers in 16 herds were sprayed on two or four occasions with insecticide, while 836 dry cows and 432 heifers in 24 herds acted as untreated controls. The insecticide significantly ( P < 0·001) reduced fly numbers on the head and flank regions of cows. In Experiment 1, six (3·3%) infections occurred in dry cows in the treated group compared with 10 (4·5%) in the control group. In Experiment 2, a significantly higher ( P < 0·05) number of infections (5·5%) occurred in dry cows in the control group than in the treated group (2·7%). However, in heifers, infection levels were higher in treated (3·1%) than in control animals (2·1%). Overall, spraying significantly ( P < 0·01) reduced summer mastitis in cows. However, when infections in heifers were included the combined results were not significantly different.
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