Effect of forage quality on digestion and performance responses of cattle to supplementation with cooked molasses blocks

We evaluated the effect of forage quality on response of cattle to supplementation with cooked molasses blocks. In Exp. 1, 175 heifers had ad libitum access to prairie hay (5.2% CP, DM basis). Treatments were a 2 x 3 factorial: supplementation with 0 or 1.96 kg/d of alfalfa DM, and supplementation with no cooked molasses block or with a low-protein or a high-protein cooked molasses block (14.4 and 27.5% CP, respectively, DM basis). There were no significant interactions between alfalfa and cooked molasses block for intake or gain. Forage intake and ADG were increased (P < 0.05) by alfalfa supplementation. Heifers fed high-protein cooked molasses blocks gained more (P < 0.05) weight than those fed low-protein cooked molasses blocks or no cooked molasses block. Heifers fed high-protein cooked molasses blocks ate more (P < 0.05) forage than those fed low-protein cooked molasses blocks, with heifers fed no cooked molasses block being intermediate. In Exp. 2, responses to cooked molasses blocks containing 33% CP (DM basis) were measured in 18 steers fed: 1) brome (8.4% CP), 2) alfalfa (19.2% CP), or 3) brome supplemented with 1.93 kg/d of alfalfa DM. Forages were available ad libitum. Forage DM intake was not affected by cooked molasses block and was greater (P < 0.05) for alfalfa than the alfalfa/brome mix, which in turn was greater (P < 0.05) than brome. Digestibility of DM was greater (P < 0.05) for alfalfa than brome or the alfalfa/brome mix and was not affected by cooked molasses block supplementation. Supplementation with cooked molasses blocks had only small effects on intake and digestion of medium- to high-quality forages, but it improved gains and feed efficiencies of heifers fed prairie hay ad libitum, with or without supplemental alfalfa.