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 degrees C for 3, 7, 15 a nd 30 min) of horse beans on potential ruminant protein nutritional values were evaluated by the new Dutch protein evaluation system: the DVE/OEB mode l. The items assessed in this experiment were: (a) rumen bypass protein (BC P); (b) rumen bypass starch (BSt); (c) fermented organic matter (FOM); (d) truly absorbed bypass protein (ABCP); (e) microbial protein synthesized in me rumen based on available energy (E_MP); (f) microbial protein synthesize d in the rumen based on available N (N_MP); (g) true protein supplied to th e small intestine (TPSI); (h) truly absorbed rumen synthesized microbial pr otein (AMP); (i) endogenous protein losses (ENDP); Ci) truly digested prote in in the small intestine (DVE) and (k), degraded protein balance (OEB). Pr essure toasting significantly increased BCP, BSt, TPSI, ABCP, DVE (P < 0.00 1) and decreased FOM, E_MP, AMP, N_MP and OEB (P < 0.001) with increasing t emperatures and times. The values of BCP, BSt, TPSI, ABCP and DVE at 136 de grees 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 degrees C/15 min were decrea sed by 28.7, 30.9, 29.0, 49.0 and 69%, respectively, over the raw horse bea ns. 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 i n microbial protein. Therefore the net absorbable DVE in the small intestin e was highly increased. The OEB values were significantly reduced (P < 0.00 1) but were not negative. Results indicated that microbial protein synthesi s 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 degrees 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 temperat ure was effective in shifting protein degradation from rumen to the intesti nes and in increasing the DVE values without reaching negative OEB values. The treatments of 100 degrees C for 7, 15 or 30 min, 118 degrees C for 3, 7 , 15 or 30 min and 136 degrees C for 3 or 7 min were not sufficient to redu ce N-loss in the rumen due to the too high OEB values. But pressure toastin g at 136 degrees C/15 min might be optimal treatments for horse beans due t o the very lower OEB values. Additional study is required concerning the ef fects of optimal pressure toasting of horse beans on animal performance. (C ) 2000 Published by Elsevier Science B.V.