Observations on fresh forage intake, ingesta particle size and nutrient digestibility in four species of macropod

Abstract

The particle-size distributions of the ingesta of the sacciform forestomach in free-ranging animals of a grazing macropod species [Macropus eugenii (tammar wallaby)], a grazer/browser [Macropus parma (parma wallaby)], a browser/grazer [Petrogale penicillata (brush-tailed rock-wallaby)] and a browser [Wallabia bicolor (swamp wallaby)] from Kawau Island, New Zealand, were compared with those of captive animals maintained on a standing ryegrass (Lolium perenne) sward. Nutrient digestibility was also measured in tammar and parma wallabies fed ryegrass or browse, i.e. fresh mahoe (Melicytus ramiflora) and this was related to particle-size distributions of the ingesta.

There were significant differences in the particle size distributions of digesta from tammar and parma wallabies in the wild but not in captivity. In free-ranging animals the ingesta from both browsing species, the brush-tailed rock-wallaby and the parma wallaby, contained consistently greater proportions of coarse particles and smaller proportions of fine particles than did those of the tammar wallaby. These differences may be correlated with reported differences in their tooth morphologies. However, the presence of significant differences in particle-size distributions of the digesta between brush-tailed rock-wallabies and parma wallabies when constrained to grass, despite reported similarities in their tooth morphology, suggests that factors other than tooth morphology contribute to differences in the oral processing of food by browsing and grazing macropods. There were greater proportions of grass fragments in the coarse than in the finer fractions of ingesta from free-ranging brush-tailed rock-wallabies, indicating that this species is less effective at chewing grass.

There were no overall differences between tammar and parma wallabies in the digestibilities of organic matter, neutral-detergent fibre (NDF) or acid-detergent fibre (ADF) but the NDF and ADF digestibilites of both species increased significantly with increase in the proportion of fine ingesta particles and with increase in mass of fermentative digesta.

These findings indicate the importance of oral processing to digestive efficiency in macropods and the relationship between oral processing and tooth morphology.