EFFECTS OF FEEDING AVOPARCIN IN COMBINATION WITH PROGESTERONE-ESTRADIOL IMPLANTS ON GROWING AND FINISHING STEERS

Abstract
Two, experiments were conducted with growing and finishing steers to determine the performance response to feeding avoparcin with or without progesterone-estradiol (Synovex-S) implants. In exp. 1, 96 crossbred yearling steers were fed diets containing 40% hay crop silage (DM basis) for 168 days. Avoparcin increased (P < 0.05) weight gains (16%) and feed efficiency (16%). Initial Synovex-S implants increased (P < 0.05) weight gain (14%) and feed efficiency (11%). Reimplanting at 112 days tended to further improve (P > 0.05) rate of gain and feed efficiency over initial implanting. In exp. 2, 80 Hereford yearling steers were fed diets containing only 19% corn silage (DM basis) for 98 days. Avoparcin had no effect on weight gain but improved (P > 0.05) feed efficiency (11%). Synovex improved (P < 0.05) weight gain (17%) and feed efficiency (11%). In both experiments treatments produced no effects on carcass measurements except for an increase in warm carcass weight. Also, in both experiments the effects of avoparcin and Synovex on feed efficiency were fully additive. Key words: Growth promotants, implants, feed additives, steers

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