Studies on the Nutrition of Macropodine Marsupials V.* Microbial Fermentation in the Forestomach of Thylogale thetis and Macropus eugenii

Rates of volatile fatty acid (VFA) and ammonia production at different sites along the forestomach of Thylogale thetis, the red-necked pademelon, and Macropus eugenii, the tammar wallaby, were measured both in vitro and in vivo. Estimates of the flow of microbial nitrogen from the stomach in vivo were also obtained. In both species VFA production was faster both in vitro (P < 0·025) and in vivo (P < 0·01) in the sacciform forestomach than in the tubiform forestomach. The ratio of total VFA production to digestible organic matter (OM) intake was similar in the two species, and similar to published estimates for ruminants. Net production of ammonia in vivo was faster (P < 0·01) in the sacciform forestomach than in the tubiform forestomach of T. thetis but not of M. eugenii. The ratio of total net ammonia production to nitrogen intake was similar in the two species, and net synthesis of microbial protein per kilogram OM apparently fermented in the stomach of both T. thetis and M. eugenii was similar to that in ruminants. The decrease in fermentation rate along the forestomach of both species was consistent with the previously reported pattern of apparent digestion of OM in the macropodine stomach. Although this pattern of microbial activity differs from that in ruminants, the overall fermentation is extensive. Thus the lower fibre digestibility often found in macropodines compared with sheep may be related to a faster rate of passage of particulate digesta through the macropodine forestomach, but it is not due to a less efficient microbial fermentation.