DIFFERENCES IN MICROBIAL FERMENTATION OF BARLEY STRAW INDUCED BY ITS TREATMENT WITH ANHYDROUS AMMONIA

The effect of ammonia treatment of straw on both the rumen environment and the extent of its microbial fermentation was studied. Four rumen cannulated sheep were randomly given 700 g/day of untreated straw plus urea (US), ammonia-treated straw (TS) and alfalfa hay (AH) in a chang e-over design with three periods. Rumen pH was lower and ammonia-nitro gen and total volatile fatty acid (VFA) concentrations were higher (P < 0.001) with AH than with LSS or TS. With the straw diets, TS promote d a lower pH than LIS (P < 0.05), but differences were less than 0.3 u nits and the mean pH was never below 6.5. There were no differences be tween the straw diets in ammonia-nitrogen or VFA concentration (P > 0. 05). When untreated barley straw (BS) and treated straw (TS) were incu bated in situ disappearance of dry matter (dDM) at 12, 24 and 48 h (P < 0.01) and neutral-detergent fibre (dNDF) at 48 h (P < 0.001) were hi gher with TS. In vitro incubation showed a higher gas production with TS only after 36 h (P < 0.05) whereas gas from BS fermentation was hig her up to 14 h (P < 0.05). Among diets, dDM, dNDF and gas production w ith US were numerically higher than with TS or AH throughout, although few significant differences were observed, except for a higher dDM at 12 (P < 0.01) and 24 (P < 0.10) h and a higher dNDF at 12 h (P < 0.10 ). Particle-associated enzymes were extracted from BS and TS incubated in the rumen for 4, 8, 12 and 24 h. Results of xylanase and cellulase activities support those of straw incubation, with a drop between 4 a nd 8 h in TS diet. The concentration of residual phenolics per unit of incubated straws after 22 and 24 h show that phenolics release to the media was higher with the TS diet. Daily changes of phenolic concentr ation into rumen liquid was also higher with TS than with US (P < 0.00 1). The increased release of straw phenolics by ammoniation reduced th e potential for rumen degradation of straw, mainly in the first hours of the fermentation period.