PRODUCTIVITY OF THE COW-CALF UNIT IN RANGE CATTLE PROTECTED FROM HORN FLIES, Haematobia irritans (L.), BY PESTICIDAL EAR TAGS

Experiments conducted on a ranch in southern Alberta evaluated the productivity of the cow-calf unit in breeding herds in response to treatment with pesticidal (8% fenvalerate wt/wt) ear tags to control infestations of horn flies, Haematobia irritans (L.). Optimum economic productivity was found to depend on the effectiveness of tags in establishing fly-free grazing (FFG) conditions and maintaining them without interruption during the complete summer grazing period. This was achieved when animals were tagged before the first overwintering horn flies emerged in spring. Present formulations of pesticide in tags will support the required FFG conditions for 85–90 d. Management of herds for maximum gains throughout the summer in southern Alberta requires fly control that will maintain FFG conditions for at least 115 d. Rates of gain in weight of animals under FFG conditions on dry range conformed with the 16% improvement in efficiency of production projected from controlled experiments on irrigated pastures. K...