Relative merits of using purified proteins and natural foods in studies of wildlife nutrition: the nitrogen requirements of a rodent pollinator

Abstract

Aethomys namaquensis is a 60 g murid rodent that is an important pollinator of several Protea species in South Africa. We compared the nitrogen requirements of this species on two different protein sources: pollen and casein. Pollen is an important source of nitrogen for specialist flower-feeding mammals in Australia. However, its value for a generalist rodent species such as A. namaquensis had not previously been assessed. Casein is often used as the source of protein in studies of wildlife nutrition, as the use of a single purified protein makes it easier for researchers to compare their results with those from other studies. The apparent digestibility of casein was significantly higher than that of pollen, 75.6 % vs 58.4 %, but the biological value was significantly lower, 39 % vs 49 %. As a result of the lower biological value the truly digestible maintenance nitrogen requirements of A. namaquensis on the casein diet were almost double those on the pollen diet (158 mg N/day vs 66 mg N/day). When these values are compared with those for other non-ruminants on natural diets, the pollen values match those predicted for a 60 g animal, while the casein values exceed the predictions. Because purified proteins, like casein, are unlikely to match an animal’s amino acid requirements closely, they may overestimate the nitrogen requirements of wild animals.