EFFECT OF HORN FLY (DIPTERA, MUSCIDAE) CONTROL DURING THE SPRING ON CALF PRODUCTION BY FALL-CALVING BEEF-COWS

In the spring of three consecutive years, horn By, Haemetobia irritans (L.), populations on fall-carving cows were reduced 82% for a 12-wk p eriod using pyrethroid-impregnated ear tags. Horn By populations on co ntrol cows exceeded 200 flies per animal for an average of 6 wk. Altho ugh the weights of cows and calves and body condition scores of both c ontrol and treated groups varied front year to year, a year x treatmen t effect (P < 0.01) on cow and calf weight gain was observed. However, differences in cow and calf production between treatments were not as sociated with differences in exposure to horn flies, and no significan t effect on weaning weight of fall-born calves was associated with hor n fly control. Calf body condition scores were also unaffected by horn fly control.