INTAKE OF LASALOCID-CONTAINING MINERAL SUPPLEMENTS BY GRAZING BEEF HEIFERS

A 2-yr grazing study was conducted to determine the effect of lasaloci d (BOVATEC) supplement, to yearling beef heifers. on growth rate, repr oductive performance and survival of horn fly larvae in feces. Lasaloc id was supplemented via a commercially prepared mineral mix offered fr ee-choice. Average daily mineral intake was 83.2 and 89.1, and 140.3 a nd 147.2 g head-1, for BOVATEC and CONTROL animals, in years 1 and 2, respectively. Mineral intake was unaffected by treatment. The variabil ity in mineral intake was high, as indicated by the large coefficients of variation: 32.1 and 29.1% in year 1 and 29.0 and 38.8% in year 2, for BOVATEC and CONTROL treated animals. respectively. Average daily g ain for BOVATEC heifers was 14.5% greater (P = 0.04) than for CONTROL heifers in year 1 even though lasalocid intake was less than the expec ted level, but only 3 % greater (P = 0.5 1) in year 2. Lasalocid had n o significant effect on reproductive performance of heifers or on horn fly larval survival in cattle feces. Horn fly larval survival showed a weak (R2 = 0.21) and negative relationship with manure nitrogen cont ent.