EFFECTS OF RUMINALLY DEGRADABLE AND ESCAPE PROTEIN SUPPLEMENTS ON STEERS GRAZING SUMMER NATIVE RANGE

One experiment was conducted during 1989 to determine whether a deficiency exists for either ruminally degradable or escape protein in steers grazing summer native range. Increasing levels of ruminally degradable (.15, .27, and .37 kg/d) and escape protein (.07, .14, and .21 kg/d) replaced a cornstarch and molasses (energy control) supplement. Supplements were isoenergetic and fed individually to steers (.88 kg/d). No response to the degradable protein supplement (P = .15) was observed; however, a linear gain response (P < .01) was observed in steers fed escape protein in addition to ruminally degradable protein. An in vitro study indicated that more (P < .01) microbial protein was synthesized from the energy supplement than from the degradable protein; this finding presumably relates to the numerical decrease in weight gains observed for steers fed degradable protein supplements. Analyses of esophageal extrusa samples indicated that CP was relatively constant for the 1989 growing season compared with the 1988 growing season (P < .05). Escape protein values differed (P < .01) between years and among months within year. Forages that were apparently grazed in 1989 were never deficient in degradable protein. Additional gain observed from feeding escape protein would indicate that microbial protein synthesis may be insufficient to satisfy the metabolizable protein requirement, which probably limited gains by steers grazing summer native range.