Pasture deworming and (or) subsequent feedlot deworming with fenbendazole. I, Effects on grazing performance, feedlot performance and carcass traits of yearling steers

Abstract

734 steers, weighing 286 kg, were used during a 118-day grazing period, after which 640 were placed in a feedlot for finishing (average of 121 days, range of 111 to 133 days) to measure the main effects and interactions of 2 pasture deworming treatments (negative control, strategically dewormed with fenbendazole) and 2 feedlot deworming treatments (negative control, dewormed with fenbendazole) on grazing performance, feedlot performance, carcass traits and production economics for yearling steers. Strategic deworming with fenbendazole (FBZ) during the grazing phase increased pasture gain by 22 kg compared with control steers. Feedlot deworming improved performance of steers in all treatments, but it had a much greater effect on performance of pasture control steers. Deworming with FBZ in the feedlot improved daily gain of pasture control steers by 13.4% compared with a 4.2% improvement for steers that had been strategically dewormed on pasture. Similarly, feedlot deworming improved feed/gain ratio by 4.65% for pasture control steers compared with 0.4% improvement for steers that had been strategically dewormed. On a carcass-adjusted basis, feedlot deworming of strategically dewormed steers increased daily gain 6.8%, and feed/gain by 2.9%. Feedlot deworming of pasture control steers increased daily dry matter intake (DDMI) by 7.8% compared with no feedlot deworming, while feedlot deworming increased DDMI by 3.2% in the same comparison for strategically dewormed steers. Carcass traits were affected similarly. Dressing percentage was increased by both strategic deworming on pasture and feedlot deworming with fenbendazole. Feedlot deworming of pasture control steers increased carcass weight by 22 kg, while feedlot deworming of steers that were strategically dewormed on pasture increased carcass weight by 9.5 kg. The percentage of choice carcasses was lower, and the percentage of select carcasses was higher for the pasture control-feedlot control steers compared with the other treatment groups. Strategic deworming during grazing resulted in a net benefit of $33.75 per head. For the complete grazing-finishing system, feedlot deworming of previously non-dewormed steers with FBZ produced a net benefit of $30.61 per head on a carcass-adjusted basis, while feedlot deworming of strategically dewormed steers produced a net benefit of $11.07. Strategic deworming of grazing steers on pasture and yearling steers that were entering the feedlot from summer pasture with FBZ produced clear performance and economic benefits.