Phosphate rather than surfactant accounts for the main contribution to enhanced fibre digestibility resulting from treatment with boiling neutral detergent

It is known that extraction of some grasses with neutral detergent (ND) inc reases the in vitro digestibility [Kennedy, P.M., Lowry, J.B., Conlan, L.L. , 1999. J. Sci. Food Agric. 79, 544]. Here, we report experiments which def ined the contribution of ND components to digestibility increases. Substrat es were prepared from spear grass (Heteropogon contortus) by boiling at neu tral pH in solutions of 0.05 M disodium EDTA, 0.018 M sodium berate, and 0. 03 M sodium phosphate, and a mixture of the three solutions. Phosphate was the most effective single component in increasing ND fibre (NDF) digestibil ity in vitro, after 120 h of fermentation, from 472 to 522 g/kg NDF, equiva lent to 68% of the increase found with boiling ND. NDF digestibility of bag asse at 120 h increased from 162 to 186, 230 and 277 g/kg NDF after boiling for 1 h in water, neutral phosphate and ND, respectively. Phosphate treatm ent of bagasse produced a 44% increase in NDF digestibility, compared to in creases of 5, 8, 14, and 16 % for rhodes grass (Chloris gayana), spear gras s, angleton grass (Dicanthium arisratum) and carpet grass (Axonopus affinis ), respectively. Increases of cumulative gas production against incubation time indicated that most of the increased fermentation had occurred by 24 h of fermentation for the grasses, whereas 72 h was needed for bagasse. Ther e were also improvements in NDF digestion with neutral phosphate treatment of spear grass at temperatures of 75, 85 or 95 degrees C, with prolonged tr eatment times required at lower temperatures. These treatments reduced the content of acid insoluble ash in NDF and increased the rate of production o f gas during fermentation. Removal of minerals from the cell wall matrix ap peared to be responsible for the increase in NDF digestibility caused by ph osphate treatment. The possible commercial use of phosphate on-farm to upgr ade nutritional quality of straws is discussed. (C) 2000 Elsevier Science B .V. All rights reserved.