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 i ncomplete Latin square with 13 treatments and four periods to evaluate the potential for different supplements to substitute for intake of l ow-quality, tallgrass-prairie forage. Steers were given ad libitum acc ess to forage and received either no supplement (control = CTL) or one of four supplements, each fed at three different levels of intake. Su pplements included 1) moderate CP (17.5%) concentrate (MCP-CON), 2) hi gh CP (32.7%) concentrate (HCP-CON), 3) long-stem alfalfa hay (LSAH; 1 7.2% CP), and 4) alfalfa pellets (AP; 16.3% CP). Concentrates were mix tures of sorghum grain and soybean meal. Supplements were fed to suppl y .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 qu adratic (P = .03) forage intake response. Offering MCP-CON higher than .10% BW of CP/d (approximately .59% BW of DM) resulted in a substitut ion rate of -.56 g of forage/g of supplement. Although effects were no t 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 increase d linearly (P <.01) across supplementation levels for HCP-CON and AP s upplements. 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 high est supplementation rate for MCP-CON and LSAH (quadratic, P less than or equal to .05). Most fermentation variables displayed positive respo nses 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 likelih ood of observing substitution effects.