Effects of supplement type on animal performance, forage intake, digestion, and ruminal measurements of growing beef cattle

Two experiments were conducted to determine the effects of supplement type on the rate of gain by heifers grazing bermudagrass and on the intake, apparent total-tract OM digestibility, ruminal fermentation, digesta kinetics, in situ DM digestibility, and forage protein degradation by steers fed prairie hay. In Exp. 1, 45 heifers (284 +/- 24 kg) grazed a bermudagrass pasture for 91 d in the late summer to determine the effects of no supplement (CON), or one of four individually fed monensin-containing (150 mg/[heifer.d]) supplements (MINCS; 0.1 kg of mineral mix with 0.2 kg [DM] of cottonseed hulls as a carrier/[heifer.d]), a pelleted protein supplement (PROT; 1 kg of DM, 242 g of degradable intake protein [DIP]/[heifer.d]), or high-fiber (HF) and high-grain (HG) (2 kg of DM, 243 and 257 g of DIP, respectively/[heifer.d]) pelleted energy supplements. In Exp. 2, four ruminally cannulated steers (311 +/- 22 kg) with ad libitum access to low-quality (4% DIP, 73% NDF, 40% ADF) prairie hay were individually fed monensin-containing (200 mg/[steer.d]) treatments consisting of 1) mineral mix + corn (MINCR; 0.1 kg of mineral and 0.4 kg of cracked corn [DM] as a carrier, 19 g of DIP/[steer.d]), 2) PROT (1.4 kg of DM, 335 g of DIP/[steer.d]), 3) HF, or 4) HG (2.9 kg of DM, 340 and 360 g of DIP, respectively/[steer.d]) in a 4 x 4 Latin square with 14-d adaptation and 6-d sampling periods. In Exp. 1, the HF-, HG-, and PROT-supplemented heifers had greater (P < 0.01) rates of gain than CON heifers, and the HF- and HG-supplemented heifers tended (P < 0.11) to gain more weight than those fed PROT. In Exp. 2, steers fed PROT consumed more (P < 0.05) hay OM than HF and HG, or MINCR. Total OM intake was greater (P < 0.01) by supplemented steers than MINCR-fed cattle. Hay OM digestibility was not affected (P = 0.19) by treatment, but total diet OM digestibility was greater (P < 0.01) for HF- and HG-than for MINCR- or PROT-fed steers. The rate of in situ DM digestibility was greater (P < 0.01) for HF, HG, and PROT than for MINCR. Results from these studies indicate that feeding milo- vs fiber-based energy supplements formulated to provide adequate DIP did not result in different forage intake, OM digestibility, or in situ DM digestibility, whereas both increased ADG in heifers consuming low-quality forages compared with unsupplemented or mineral- or protein-supplemented cattle. An adequate DIP:TDN balance decreased the negative associative effects often observed when large quantities of high-starch supplements are fed with low-quality hay.