[Economic significance of the prevention of losses caused by blood-sucking diptera in grazing dairy cows].

It was was demonstrated in an experiment that the blood-sucking dipterous insects adversely affected the efficiency of cows on pasture; these cows showed a significantly decreased milk yield and milk fat percentage. The experiment was conducted in South Bohemia at Chlum u Trebonĕ where seven species of gnats occurred in considerable abundancy, including the largest populations of Aedes sticticus (Meig.), Ae. cinereus Meig., Ae. vexans Meig. and Ae. punctor Kirby, which represented more than 80% of all gnats, and where gad-flies lived at the same time, represented by 18 species of five genera, chief among which were the species Tabanus bromius (L.) and T. maculicornis (Zett.), forming over 60% of all gad-flies. The experiment with 25 control dairy cows of the Bohemian Spotted breed lasted 62 days (July, August 1977). Diethyltoluamide in a 10% water emulsion was used as repellent with which cows were sprayed (with a special spraying apparatus) in 48h intervals. In the experimental (sprayed) cows, compared with the untreated control cows, milk yield per head per day increased by 6.23%, i. e. 43.56 kg milk, and butterfat percentage increased by 11,81%, representing 3.62 kg per head per day. In conversion to fat-corrected milk (milk with a constant 4% fat content), milk yield increased by 9.69%. In conversion to values per 1000 cows on pasture the net value of milk increased by 709.41 Kcs per day. The return rate of the money expended is 1.31 crowns. The results were statistically significant to highly significant.