Digestibility and Rumen Escape of Soybean Meal, Blood Meal, Meat and Bone Meal and Dehydrated Alfalfa Nitrogen

Acid detergent insoluble nitrogen (ADIN), acid pepsin insoluble nitrogen (APIN), true nitrogen (N) digestibility, in situ residual N and ruminal N escape were determined for various protein sources. The ADIN and APIN of soybean meal (SBM), blood meal (BM), meat and bone meal (MBM) and dehydrated alfalfa (DA) were measured in Exp. 1. Soybean meal and BM contained the lowest amount of ADIN and APIN, DA contained the highest and MBM was intermediate (P<.05). True digestibility of SBM, BM, MBM and DA was estimated with sheep by regressing N digested against three levels of N intake for each protein source. Estimated true digestibilities were 100.4, 99.1, 86.4 and 85.2% for SBM, BM, MBM and DA, respectively. True digestibility of SBM was greater than MBM (P<.12) and DA (P<.07), but not greater than BM. Nitrogen escape of SBM, BM, MBM and DA was determined in continuously-fed steers. Lanthanum, Cr-EDTA and diaminopimelic acid served as markers for solid, liquid and bacterial N flow, respectively. Percentage N escape of SBM, BM, MBM and DA was 28.7, 81.7, 49.3 and 66.3, respectively. Nitrogen escape of SBM was lower (P<.05) than for BM, MBM and DA. Supplementation with BM or DA resulted in greater (P<.05) N flow to the duodenum than supplementation with SBM. Digestible N escape was estimated by combining true digestibility and N escape data. In situ residual N of SBM was lower (P<.05) than residual N of BM and DA after 3, 6, 12 and 24 h of incubation. Residual N of SBM was only lower (P<.05) than MBM after 12 h of incubation. There were no differences (P>.05) due to protein source in rate of in situ N disappearance from 3 to 12 h. In situ residual N at 3, 12 and 24 h was correlated (P<.05) with percentage N escape of SBM, BM, MBM and DA.