The effects of ruminal escape protein or fat on ruminal characteristics of pregnant winter-grazing beef cows.

: The effects of ruminal escape protein and added fat on ruminal characteristics were determined at 9, 4 and 1 wk prior to calving in 20 prepartum beef cows. Cows grazed native foothills range from mid-December to early March in two different years. Cows were randomly allotted to five groups (four cows per group) and fed (g/d) either no supplement (control); 570 soybean meal (SOY); 450 soybean meal and 230 blood meal (SOY+BM); 140 soybean meal, 16 urea and 450 corn gluten mean (SOY+CGM); or 570 soybean meal and 210 animal fat (SOY+FAT). Supplements were designed to supply similar quantities of ruminally degraded protein while varying in escape protein quantity and source (SOY+BM and SOY+CGM). Control animals had the lowest (P less than .03) ruminal ammonia concentration (4.5 to 8.9 mg/dl), but values were similar (8.1 to 12.3 mg/dl) for the other treatments. In both trials, NDF disappearance rate was lowest for the control, 1.85%/h (P less than .01), and tended to be lower (P less than .07) in SOY (2.25%/h) than for the mean of SOY+BM and SOY+CGM (2.62 and 2.84%/h). Ruminal fluid volume tended to be greater (P less than .14) and dilution rate lower (P less than .13) for the mean of SOY+BM and SOY+CGM than for SOY in both trials. Particulate dilution rate was lower (P less than .01) for the mean of SOY+BM and SOY+CGM (2.33 and 2.75%/h) than for SOY+FAT (3.17%/h) in Trial 2. These results indicate that supplemental escape protein from blood meal or corn gluten meal can influence ruminal characteristics, perhaps due to a continuous release of amino acids and(or) branched-chain organic acids.