Ractopamine hydrochloride effects on feedlot performance, carcass traits, and chemical composition of feedlot steers
Schluter, Alan Ray
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A total of 160 predominantly Angus, medium-framed steers (389 kg) were fed a finishing diet for 42 to 49 d. When the steers weighed an average of 452 kg, an ultrasound measurement of fat thickness at the 12th rib indicated they were 46 d from slaughter condition. They were allotted by weight and fat thickness to five blocks of four pens of eight steers. The steers were fed ractopamine hydrochloride, a beta-adrenergic agonist, at 0, 10, 20 or 30 ppm of diet for 46 d before slaughter. Steers were commercially slaughtered and carcasses were graded 24 h postmortem for all USDA yield and quality grade factors. Forty sides (10 per treatment) were randomly selected for carcass fabrication, dissection and chemical analyses. The most notable effect of feeding ractopamine to these steers was on feedlot performance. Feeding the steers ractopamine at 20 or 30 ppm in the diet increased average daily gain, feed efficiency, final live weight and hot carcass weight (P < .05) over the controls. Other carcass traits and chemical composition of the carcasses were not influenced by ractopamine feeding (P > .05), which could be a result of a somewhat low average daily gain (1.05 kg'd"-'-) of the steers. Thus, increased level of ractopamine did not decrease USDA quality grade, but the feeding of ractopamine at 2 0 or 30 ppm levels enhanced feedlot performance and may allow cattle to be fed to heavier weights without increased carcass fatness or a decline in USDA quality grade.