Two studies will be conducted to determine energy and protein requirements, as well as the carcass and meat traits of feedlot ½ Dorper × ½ Santa Inês crossbred lambs fed diets with different quality roughages. In the first study, 84 lambs weaned at 56 days of age will be assigned, according to the initial body weight, to one of two groups (VBQ - animals fed with a diet composed by a low quality roughage; and VAQ - animals fed with a diet composed by a high quality roughage) to determine their nutritional requirements based on a comparative slaughter trial. Seven animals of each group will be used to estimate body composition of lambs at the beginning of the experiment (baseline group). After, twenty one lambs of each group will be fed ad libitum and slaughtered either at 25, 35 or 45 kg BW. The remaining 14 lambs of each group will be then assigned to 2 levels of intake, either 75 or 55% of the ad libitum intake, being slaughtered concomitant with lambs of the 45 kg BW group. Total body N, fat and energy contents will be determined. Additional experiments (an in vivo digestibility and an in vitro gas production trial) to measure diet metabolizable energy and protein contents will be conducted. In the second study, the objective is to evaluate carcass traits, centesimal composition and fat acid profile of the meat from lambs fed diets with different quality roughages, and slaughtered either at 25, 35 or 45 kg BW.
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