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Influence of Protein Degradability in Range Supplements on Abomasal Nitrogen Flow, Nitrogen Balance and Nutrient Digestibility¹

University of Nebraska, North Platte Station, North Platte 69101

Abstract

Two metabolism trials were conducted with yearling steers fed mature native forage to measure the effect of supplemental protein degradability on selected metabolic variables. Supplements contained 40% crude protein equivalence. In Trial 1, four abomasal-cannulated steers weighing 290 to 379 kg were fed supplements containing the following N sources: (1) 15% corn, 85% urea (U); (2) 100% soybean meal (SBM); (3) 10% corn, 40% soybean meal, 50% urea (SBM-U) and (4) 14% corn, 36% blood meal, 50% urea (BM-U). Equal portions of the daily diet (2.2% of body weight) were fed every 2 h. Treatment differences were not significant for organic matter digestibility, abomasal organic matter flow, nonammonia N flow, feed N flow, bacterial N flow and efficiency of microbial protein synthesis. There was a positive (P<.05) relationship between quantity of slowly degraded protein fed and nonammonia N flow (r=.97) or feed N flow (r=.98). Escape N was determined to be 21.5, 16.5 and 54.2% in SBM, SBM-U and BM-U supplements, respectively. In the second trial, no supplement, SBM, SBM-U and BM-U were fed in a N balance trial. Dry matter, crude protein and neutral detergent fiber digestibilities were higher (P<.05) for steers fed supplemented diets. Acid detergent fiber digestibility was higher (P<.05) for steers supplemented with SBM than steers fed the unsupplemented diets. Nitrogen retention was greater (P<.05) for cattle fed SBM and BM-U than for cattle fed SBM-U or no supplement. These data suggest that a BM-U supplement can be utilized as effectively as a SBM supplement when fed to steers consuming low-quality native forage in confinement.

¹ Published as Paper No. 7324 Journal Ser. Nebraska Agr. Exp. Sta.

² Anim. and Range Sci. Dept., Montana St. Univ., Bozeman 59717.

³ Anim. Sci. Dept., Univ. of Nebraska, Lincoln 68583.