Using the DVE/OEB model to determine optimal conditions of pressure toasting on horse beans (Vicia faba) for the dairy feed industry

The effects of pressure toasting (100, 118 and 136°C for 3, 7, 15 and 30 min) of horse beans on potential ruminant protein nutritional values were evaluated by the new Dutch protein evaluation system: the DVE/OEB model. The items assessed in this experiment were: (a) rumen bypass protein (BCP); (b) rumen bypass starch (BSt); (c) fermented organic matter (FOM); (d) truly absorbed bypass protein (ABCP); (e) microbial protein synthesized in the rumen based on available energy (E_MP); (f) microbial protein synthesized in the rumen based on available N (N_MP); (g) true protein supplied to the small intestine (TPSI); (h) truly absorbed rumen synthesized microbial protein (AMP); (i) endogenous protein losses (ENDP); (j) truly digested protein in the small intestine (DVE) and (k), degraded protein balance (OEB). Pressure toasting significantly increased BCP, BSt, TPSI, ABCP, DVE (P<0.001) and decreased FOM, E_MP, AMP, N_MP and OEB (P<0.001) with increasing temperatures and times. The values of BCP, BSt, TPSI, ABCP and DVE at 136°C/15 min were increased by 213.0, 83.0, 66.1, 246.1 and 90.1% and the values of FOM, E_MP, AMP, N_MP and OEB at 136°C/15 min were decreased by 28.7, 30.9, 29.0, 49.0 and 69%, respectively, over the raw horse beans. The results indicated that although pressure toasting reduced microbial protein synthesis due to reducing FOM, TPSI didn’t decrease but increased substantially because BCP more than enough to compensate for the decrease in microbial protein. Therefore the net absorbable DVE in the small intestine was highly increased. The OEB values were significantly reduced (P<0.001) but were not negative. Results indicated that microbial protein synthesis might not be impaired due to the sufficient N supplied in the rumen, but the high positive OEB values in the most treatments except 136°C/15 min (The OEB values: 31.9 g/kg DM) indicated that there were large losses of N in the rumen. It was concluded that pressure toasting at high temperature was effective in shifting protein degradation from rumen to the intestines and in increasing the DVE values without reaching negative OEB values. The treatments of 100°C for 7, 15 or 30 min, 118°C for 3, 7, 15 or 30 min and 136°C for 3 or 7 min were not sufficient to reduce N-loss in the rumen due to the too high OEB values. But pressure toasting at 136°C/15 min might be optimal treatments for horse beans due to the very lower OEB values. Additional study is required concerning the effects of optimal pressure toasting of horse beans on animal performance.