Estimating fat reserves in the brush-tailed possum, Trichosurus vulpecula Kerr (Marsupialia : Phalangeridae)

Abstract

Two hundred possums were collected from an area in Westland, New Zealand. Their carcasses were macerated and total fat content was determined by chemical means. The reliability of existing indices (visual, kidney fat, back fat, marrow fat) for predicting the proportion of total fat in the body was investigated. Two indices were developed and tested; one based on fat depots in the mesogastrium, the other based on deviations from a standardized weight for length. The index based on weight deviations gives good results if derived from a large sample of animals, and has the advantage that it can be used on live animals under sedation. The marrow fat index gives good results if fat reserves are low, and the mesogastric index does at other times, when estimates are obtained by autopsy of a few animals. Analysis of variance showed that, within the population studied, time of the year and a season-age interaction were the only significant sources of heterogeneity in fat reserves.