Digestibility and retension of food components in caged mountain hares Lepus timidus during the winter

Adult mountain hares in outdoor cages were studied in order to evaluate the consumption and the digestibility of natural winter foods. Food, feces and urine were analysed for nitrogen, phosphorus, calcium, potassium, magnesium and sodium, and food and feces for fiber as well. The metabolism of the different nutrients are presented in this paper.
When energy equilibrium was maintained hares assimilated as an average 21.6 g dry matter per kg body weight and day (29.5 g kg^0-75). The fiber fraction showed a low digestibility ranging from 10 to 30% between different food species.
At energy equilibrium nitrogen equilibrium was usually also achieved; the hares then digested approximately 0.20–0.25. g nitrogen per kg body weight and day (0.27–0.34 kg ^-0.75). The apparent nitrogen digestibility was low, usually below 40%.
The demand for calcium, potassium and magnesium seemed to be well covered via the food. Phosphorus on the other hand was absorbed in small amounts only, which may sometimes have been insufficient. A negative sodium balance occurred when the hares were fed heather or the finest twigs of birch. Due to the low concentrations in the food this could create problems in the supply of sodium.