DIGESTIVE STRATEGIES OF THE WOMBATS - FEED-INTAKE, FIBER DIGESTION, AND DIGESTA PASSAGE IN 2 GRAZING MARSUPIALS WITH HINDGUT FERMENTATION

The wombats are grazing marsupials from mesic (Vombatus ursinus) and xeric (Lasiorhinus latifrons) regions of Australia. Feed intake and digestive responses of four wombats of each species were compared on two dietary fiber levels with pelleted straw-based diets of 59% and 44% neutral detergent fiber (NDF), and on two feed particle sizes with unpelleted and pelleted alfalfa hay. Dry matter (DM) intakes were similar between fiber levels but digestibilities of DM and NDF were greater on the low-fiber diet, with a trend to longer retention of digesta markers than on the high-fiber diet. Particulate ((103)Ruphenanthroline) and fluid ((51)CrEDTA) digesta markers were excreted in similar patterns, but mean retention times were longer for particles than for fluids (52-62 h vs. 30-36 h on the high-fiber diet). Marker excretion patterns and digestive tract anatomy were integrated into a model of digesta flow where axial flow of digesta was combined with irregular mixing along the haustrated proximal colon. Patterns of fecal particle size distribution and DM intake of the alfalfa hays indicated a more thorough comminution of feed in the dental mill of Lasiorhinus than of Vombatus. The digestive strategies of the wombats feature enhanced digestive tract capacity (Vombatus) or length (Lasiorhinus) combined with low feed intakes, which result in long retention of digesta and yield fiber digestibilities similar to those of equids and macropod marsupials. These strategies enable wombats to utilize small home ranges with pastures of poor quality and/or low abundance.