Energy source and ionophore supplementation effects on lamb growth, carcass characteristics, visceral organ mass, diet digestibility, and nitrogen metabolism

In Exp. 1, 72 Targhee lambs (initial BW 22.1 +/- .3 kg) were used to determ ine the effects of energy source (alfalfa pasture vs limit-fed, all-concent rate) and ionophore addition on performance, visceral organ mass, and carca ss characteristics. There were no differences (P > .10) in ADG or gain/feed due to ionophore supplementation. Lambs that grazed alfalfa had greater (P < .05) liver, omasum, abomasum, small intestine, cecum, and large intestin e weights than did lambs fed the concentrate diet. Lambs fed the concentrat e diet had greater (P < .01) hot carcass weights, larger (P < .01) loin eye areas, and greater (P < .001) dressing percentages than lambs that grazed alfalfa. In Exp. 2, lambs offered the concentrate diet had greater (P < .00 1) DM and OM digestibilities than lambs offered alfalfa (89.5 and 91.1 vs 7 2.4 and 74.2%, respectively). Apparent and true N digestibilities were grea ter (P < .001) for the concentrate diet than for alfalfa (90.9 and 101.7 vs 77.7 and 91.9%, respectively). Likewise, grams of N retained per day were twice as great (P < .001) with the concentrate diet than with alfalfa (14.9 vs 6.0 g/ d). The greater visceral organ mass and resulting increases in e nergy and protein requirements in lambs that grazed alfalfa were probably r esponsible for the lesser hot carcass weight and dressing percentage compar ed with lambs fed 100% concentrate.