Effects of ruminal administration of supplemental degradable intake protein and starch on utilization of low-quality warm-season grass hay by beef steers

Hereford x Angus steers were used in a 13-treatment, four-period, incomplet e Latin square design to examine the effects of starch and degradable intak e protein (DIP) supplements on forage utilization and ruminal function. Ste ers were given ad libitum access to low-quality hay (4.9% CP) and were not supplemented (NS) or received different amounts of starch (cornstarch grits ; 0, .15, and .3% of initial BW) and DIP (Na-caseinate; .03, .06, .09, and .12% of initial BW) administered via ruminal fistulae in a 3 x 4 factorial arrangement of treatments. Supplemented steers consumed more (P < .01)forag e OM, total OM, NDF, and digestible OM (DOM) than NS steers. Forage OM, tot al OM, NDF, and DOM intakes increased linearly (P < .01) as the amount of s upplemental DIP increased. The addition of starch to supplements linearly d ecreased (P < .01) the intake of forage OM, NDF, and DOM. The digestion of DM, OM, and NDF increased linearly (P < .01) with supplemental DIP and decr eased linearly (P less than or equal to .06) with supplemental starch. Part iculate and liquid passages generally increased with DIP; however, starch l evel influenced the nature of the response ( P = .03 and .06, respectively) . Similarly, ruminal acid detergent-insoluble ash content generally decreas ed as starch increased, but the effect was dependent on DIP level (P < .01) . Supplementation increased (P < .01) ruminal NH3 and total VFA and decreas ed (P < .01) ruminal pH relative to NS. All treatments supported average pH values in a range (6.3 to 6.7) unlikely to inhibit fibrolytic bacteria. Ru minal NH3 concentration increased quadratically (P = .03) with DIP and decr eased linearly (P = .02) with starch. As DIP increased, total VFA concentra tion increased linearly (P = .02). Providing supplemental DIP to steers fed low-quality forage increased OM intake and digestion, whereas addition of starch to supplements decreased forage intake and digestion.