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Intestinal digestibility of amino acids in rumen undegradable protein estimated using a precision-fed cecectomized rooster bioassay: I. Soybean meal and SoyPlus¹

S. E. Boucher^*,2, S. Calsamiglia, C. M. Parsons, H. H. Stein, M. D. Stern, P. S. Erickson^*, P. L. Utterback and C. G. Schwab^*,3

^* Department of Biological Sciences, University of New Hampshire, Durham 03824
Facultad de Veterinaria, Universitat Autònoma de Barcelona, Bellaterra, Spain 08193
Department of Animal Sciences, University of Illinois, Champaign 61801
Department of Animal Science, University of Minnesota, St. Paul 55108

³ Corresponding author: charles.schwab{at}unh.edu

The objectives of this experiment were to measure intestinal digestibility of AA in rumen undegradable protein (RUP-AA) in soybean meal (SBM) and expeller SBM (SoyPlus, West Central, Ralston, IA; SP) and to determine if these feeds contain a constant protein fraction that is undegradable in the rumen and indigestible in the small intestine, as assumed in the French Institut National de la Recherche Agronomique (Paris, France) and Scandinavian AAT-PBV (AAT = AA absorbed from small intestine; PBV = protein balance in the rumen) models. Three samples of SBM and 3 samples of SP were obtained from the Feed Analysis Consortium Inc. (Savoy, IL). To obtain the RUP fraction, samples were ruminally incubated in situ for 16 h in 4 lactating cows, and the collected rumen undegraded residues (RUR) were pooled by sample. Subsamples of the intact feeds and RUR were crop intubated to 4 cecectomized roosters, and total excreta were collected for 48 h. Intact feeds, RUR, and excreta were analyzed for AA. Basal endogenous AA loss estimates were obtained from fasted birds and were used to calculate standardized digestibility of AA in the intact feeds and RUP-AA. Indigestibility coefficients of the intact feeds were calculated as (100 – % standardized AA digestibility), and indigestibility of the RUR was calculated as {(100 – % ruminal degradation of AA) x [(100 – % standardized RUP-AA digestibility)]/100}. Results indicated that standardized digestibility of feed-AA was similar to standardized digestibility of RUP-AA for SBM and SP samples and that standardized digestibility of individual AA differed within samples. Standardized feed-AA and RUP-AA digestibility values were lowest for Lys and Cys and highest for Trp and Met. Results also indicated that SBM and SP did not contain a constant protein fraction that was both undegradable in the rumen and indigestible in the small intestine. Indigestibility values of RUR were lower than in intact feeds, suggesting that SBM and SP contain a protein fraction that is indigestible in the intestine but partly degradable in the rumen, digestible in the intestine after ruminal incubation, or both.

Key Words: amino acid digestibility • rumen-undegradable protein • soybean meal

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				S. E. Boucher, S. Calsamiglia, C. M. Parsons, H. H. Stein, M. D. Stern, P. S. Erickson, P. L. Utterback, and C. G. Schwab Intestinal digestibility of amino acids in rumen-undegraded protein estimated using a precision-fed cecectomized rooster bioassay: II. Distillers dried grains with solubles and fish meal J Dairy Sci, December 1, 2009; 92(12): 6056 - 6067. [Abstract] [Full Text] [PDF]