In vitro gas production and substrate digestion relationship for a buffer free of indirect gas production

JAURENA, G.; WAWRZKIEWICZ, M.; PALLADINO, R. A. AND DANELóN, J. L.

Dublin

Congreso; 58th Annual Meeting of EAAP; 2007

Dublin

A constant gas production (GP) to dry matter (DM) digested relationship is a basic assumption of the GP technique. The aim of this study was to verify if this relationship was constant along the time of incubation (H) for fresh alfalfa incubated at different pH and using a non-conventional buffer. Fresh alfalfa samples were incubated at 4 pH (T6.8, T6.3, T5.8 and T5.3) in 3 periods using a phosphate-citrate buffer instead of the conventional carbonate-bicarbonate buffer. The GP was measured at 1, 2, 4, 6, 9, 12, 16, 20, 24, 30, 36 and 48 h and the DM disappeared (DMD) was estimated by collecting the digestion residues at 6, 12, 24 and 48 h. Data were analysed by linear regression and ANOVA. The best adjustment for regression of GP on DMD was obtained by splitting the data set by H (H=6 and H > 6) so that the intercept (á) was respectively -38 ml (P<0.01) and -12 ml (P>0.05). The slope of GP on DMD was 0.18 ml/g DMD (P<0.01) for both H. The GP/DMD ratio was affected by pH (ml/g DMD, 0.15a, 0.13ab, 0.12b and 0.12b respectively for T6.8, T6.3, T5.8 and T5.3, different letters differ P < 0.05) and by H (H=6, 0.06; H>6, 0.16 ml/g DMD; P<0.01). These results indicate that the GP was proportional to DMD and remained constant along the incubation for the new buffer, but suggest that part of the material measured as digested was lost during filtrate at early times of incubation (as indicated by á<0 for H=6), and that this effect was higher at low pH.