Evaluation of the potential of supplements to substitute for low-quality, tallgrass-prairie forage.

Thirteen ruminally fistulated steers (260 +/- 15 kg) were used in an incomplete Latin square with 13 treatments and four periods to evaluate the potential for different supplements to substitute for intake of low-quality, tallgrass-prairie forage. Steers were given ad libitum access to forage and received either no supplement (control = CTL) or one of four supplements, each fed at three different levels of intake. Supplements included 1) moderate CP (17.5%) concentrate (MCP-CON), 2) high CP (32.7%) concentrate (HCP-CON), 3) long-stem alfalfa hay (LSAH; 17.2% CP), and 4) alfalfa pellets (AP; 16.3% CP). Concentrates were mixtures of sorghum grain and soybean meal. Supplements were fed to supply .05, .10, and .15% BW of CP/d. Forage intake and digestible DMI were increased (P < .01) for supplemented steers compared with CTL (22 and 96%, respectively). Steers receiving increasing MCP-CON exhibited a quadratic (P = .03) forage intake response. Offering MCP-CON higher than .10% BW of CP/d (approximately .59% BW of DM) resulted in a substitution rate of -.56 g of forage/g of supplement. Although effects were not significant for steers receiving LSAH, the decline in forage intake at the high level of supplementation (-.48 g of forage/g of supplement) was similar in magnitude to that for MCP-CON. Forage intake increased linearly (P < .01) across supplementation levels for HCP-CON and AP supplements. Passage rates were faster (P < .01) for supplemented steers. However, passage rates for HCP-CON and AP groups increased linearly (P < .01) with increasing supplement, whereas they declined at the highest supplementation rate for MCP-CON and LSAH (quadratic, P < or = .05). Most fermentation variables displayed positive responses to supplementation per se and to increasing amount of supplements offered. In conclusion, although supplementation effectively enhances the use of low-quality forage, supplement type may affect the likelihood of observing substitution effects.