Growth and carcase quality of lambs fed concentrate rations in a feedlot

Two feedlot experiments were conducted during 1967 and 1968 using crossbred lambs and concentrate rations. In experiment 1, in 1967, seven rations at three crude protein levels (approximately 15, 21, and 29 per cent) and with various constituents were fed to lambs selected at 50 lb bodyweight. Three rations were in both the pelleted and the dry mash form. Growth rate, efficiency of feed conversion, and carcase quality were measured. After an initial period of twelve days, when all lambs lost weight, lambs on the pelleted diets grew faster than those on the mash diets, but there were no differences due to protein level or to the various constituents in the diets. In experiment 2, in 1968, three pelleted diets were compared, two at low and high crude protein from experiment 1 (17 and 31 per cent), and the third at 19 per cent. Four treatments were included within each diet to overcome the initial period of weight loss : a. diet alone, b. diet and 30 per cent hay decreasing to none after 12 days, c. diet with 3 per cent calcium carbonate included throughout the experiment, d. diet with 3 per cent CaCO3 included, plus hay for the first 12 days. Hay overcame the initial weight loss and low rumen pH, but subsequently the lambs fed the lowest protein diet with 3 per cent CaCO3 grew faster and were the most efficient. Dry matter digestibility and nitrogen retention were also compared in a metabolism trial for the three diets in experiment 2.