Effects of level and source of carbohydrate and level of degradable intakeprotein on intake and digestion of low-quality tallgrass-prairie hay by beef steers

Ruminally fistulated steers (n = 13; 263 kg) were used in an incomplete Lat in square with 13 treatments and four periods to evaluate the effects of le vel and source of supplemental carbohydrate (CHO) and level of degradable i ntake protein (DIP) on the utilization of low quality, tallgrass-prairie ha y. Steers were given ad libitum access to forage (5.7% CP, 2.6% DIP, and 74 .9% NDF). The supplementation treatments were fashioned as a 2 x 3 x 2 fact orial arrangement plus a negative control (NC; no supplement). The factors included two DIP levels (.031 and .122% BW) and three CHO sources (starch, glucose, and fiber) fed at two levels (.15 and .30% BW) within each level o f DIP supplementation. The effect of supplementation on forage OM intake (F OMI) was dependent (P < .01) on level and source of CHO and level of DIP fe d. When DIP was low, forage, total, and digestible OM intakes were generall y greater for the starch treatment than for the nonstarch treatments. Howev er, when the DIP level was high, intakes were greater for the nonstarch (i. e., fiber and glucose) treatments. Generally, FOMI decreased (P < .01) when more supplemental CHO was provided. Supplementation typically increased fi ber digestion, but the response was dependent (P <.01) on level and source of CHO and level of DIP. Generally, supplements with low levels of CHO impr oved NDF digestion (NDFD). However, supplements with the high level of CHO decreased NDFD, except for fiber at the high level of DIP. Organic matter d igestion was increased by supplementation, but the impact of increasing CHO was dependent (P <.01) on source of CHO and level of DIP. Supplementation treatments had significant impact on ruminal pH, NH3 N, and the total conce ntration of organic acids as well as their relative proportions. In conclus ion, supplemental DIP enhanced the use of low-quality forage; however, the impact of supplemental CHO on low-quality forage use was dependent on sourc e and level of CHO offered, as well as the level of DIP provided.