Abstract: Problem statement: Guar meal is a by-product consisting of hull and germ and is mostly used as a protein source in poultry and ruminant rations. The aim was to determine the effect of heat or heat-xylose processing on nitrogen fractions, in situ ruminal degradation parameters and in situ/in vitro ruminal and post-ruminal disappearance of guar meal. Approach: Samples were intact Guar Meal (GM), heat processed GM (GMhp, GM was heated at 100°C for 45 minute using industrial heater) and heat-xylose processed GM (GMhx, xylose was included in GM to give a final concentration of 10 g kg−1 DM, then was heat processed at 100°C for 45 minute using industrial heater). Ruminal degradation parameters of DM and Crude Protein (CP) were determined by in situ technique using four ruminally fistulated sheep. Post-ruminal disappearance of ruminal-undegradable CP was determined on residue from 16 h ruminal incubation of guar meal samples by three-step in situ/in vitro enzymatic procedure. Results: Non-protein nitrogen of the GMhx and GM samples ranged from 218-319 (g kg−1 N). Acid detergents insoluble nitrogen concentration of both GM and GMhp was significantly lower than that of GMhx (10.3, 11.29 and 18.53 g kg−1 nitrogen, respectively). In situ fractional degradation rate constant (c) of DM and CP was significantly decreased as a result of heat-xylose processing. Effective crude protein degradability of GMhp and GMhx was higher than that of GM. Post-ruminal disappearance of ruminal-undegradable CP of GM hx (0.965) was significantly higher compared with GM and GMhp (0.918 and 0.906, respectively). Conclusion: Results of the present study demonstrated that heat and heat-xylose processing might effectively protect the DM and CP of guar meal from ruminal degradation.

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