1. Use of Exogenous Fibrolytic Enzymes and Bluegrass Seed Straw in Wintering Beef Cow Feeding Regimes J.I. Szasz†, C.W. Hunt†, K.A. Johnson‡, J.J. Michal‡, and D.J. Coonrad‡ †University of Idaho and ‡Washington State University Research Objective To examine the impact of ammoniation and exogenous fibrolytic enzyme on performance of cows fed bluegrass straw diets. Introduction Open-field burning of crop aftermath has been a critically important management practice for grass seed production. This practice serves numerous agronomic benefits and provides for sustained (>10 yr) seed production from perennial grass fields. Environmental and health concerns have resulted in legislation that restrict the burning of crop residues in many portions of the Northwest. As a result, bluegrass straw has become a readily available forage source for livestock producers. However, high fiber content characteristic of straws requires that methods be implemented that improve its feeding value. Research has indicated that exogenous fibrolytic enzymes may increase fiber digestibility (Beauchemin et al., 1995 and Feng et al., 1996). By improving fiber digestibility, fibrolytic enzymes may have a practical application in feeding systems that utilize bluegrass straw. Implications Addition of enzymes was not beneficial indicating that optimal fiber digestion was achieved by ruminal microorganisms without the complement of exogenous enzymes Bluegrass straw proved to be an acceptable component of wintering beef cow rations; however the benefit achieved from ammoniation did not justify its replacement value of alfalfa hay ($19.80 cost of ammoniation per MT of straw versus $104.50 cost per MT of alfalfa hay). Home of “Idaho Gem” Materials and Methods  Completely randomized block design using 89 Angus crossbred beef cows (mean initial BW 636 kg; blocked by days-to-parturition)  Dietary treatments consisted of alfalfa in combination with:  Enzyme application method:  Non-ammoniated bluegrass straw  Ammoniated bluegrass straw  Non-ammoniated bluegrass straw with enzyme  Ammoniated bluegrass straw with enzyme  Contained xylanase and cellulase activity  676  mol reducing sugars/g CP/min (20.9% CP)  Enzyme was administered to straw by hand-spraying freshly prepared enzyme solution onto straw at a rate of 0.22 g enzyme (4.4 IU xylanase)/kg  Alfalfa was offered at a rate of 6.3 and 4.6 kg/hd/d for non- ammoniated and ammoniated straw treatments, respectively  Bluegrass was offered ad libitum and intake was recorded daily  Fibrolytic enzyme: P=.09 No differences were observed for reproductive performance: Pregnancy rate at 30 and 60 days of the breeding season. Services per conception Percent cows open With the general absence of treatment differences for calf weight, cow BCS, and reproduction, we conclude that: Exogenous fibrolytic enzymes were not beneficial Ammoniation of bluegrass straw was effective in reducing dependence on more expensive alfalfa hay as a component of a winter feed ingredient for late gestation and early post-partum beef cows.