Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 7/25/2002
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: In situ procedures may overestimate microbial degradation because soluble protein, that still can escape the rumen, is assumed to be degraded when it is solubilized. Effect of extracting soluble proteins on the ruminal degradabilities was assessed in four protein sources: solvent soybean meal (SSBM), expeller soybean meal (ESBM), blood meal (BM) and corn gluten meal (CGM). Ground (Wiley mill, 2 mm screen) samples of each were either unprocessed or extracted for 16 h in McDougall¿s buffer (70 g protein source/L buffer) at 39 C. Extracts were filtered (Whatman no. 1 paper) and residues dried (48 h; 60 C) and ground (2 mm). Ground, extracted samples were sieved and particles > 0.5 mm retained for in situ and in vitro studies. Extracted proteins were added to dacron bags; bags were soaked in buffer then inserted into the rumens of two cannulated cows. Duplicate bags for each protein were removed after 0 (washed only), 4, 8, 12, 16, 24, 48, 72, and 96 h of incubation, then washed, dried (24 h, 60 C) and residues ground (2 mm). Mixed microbes were isolated from ruminal contents from the cows; in situ residues and mixed microbes were analyzed for total N and purines. The inhibitor in vitro (IIV) procedure also was used to determine rate and extent of ruminal degradation of both unprocessed and extracted proteins. As expected, there were wide differences (P < 0.01) among proteins in degradation rate (ranging from 0.02/h (CGM) to 0.08/h (SSBM) by in situ, and from 0.01/h (BM) to 0.11/h (SSBM) by IIV) and estimated ruminal escape (ranging from 42\% (SSBM) to 75\% (BM) by in situ, and from 36\% (SSBM) to 90\% (BM) by IIV). There were trends (P = 0.08) for more rapid in situ rates with unprocessed than extracted proteins and with the use of the microbial correction. However, estimated escapes were not affected by protein extraction (P = 0.17) or by microbial correction (P = 0.38). Buffer extraction did not alter rates (P = 0.37) or escapes (P = 0.42) estimated by the IIV method. Moreover, degradation rates (P = 0.12) or ruminal escapes (P = 0.52) did not differ between the in situ or IIV method. These results suggest that rapid loss of soluble proteins during in situ incubations does not excessively inflate estimates of ruminal protein degradation.