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Description:
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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 . |