COEFFICIENTS OF DIGESTIBILITY AND NUTRITIONAL VALUES OF GEOPHYTES ANDTUBERS EATEN BY SOUTHERN AFRICAN MOLE-RATS (RODENTIA, BATHYERGIDAE)

Subterranean rodents have high energy requirements when they are excav ating their burrows. This study investigates the energy available to, and the efficiency with which it can be extracted by, four species of bathyergid mole-rats fed natural diets ranging from the underground st orage organs of geophytes to grass roots and leaves. The digestibility coefficients of geophytes ranged from 53% for the fibrous tuber of th e gemsbok cucumber to 95.7% for corms and bulbs. One species, Bathyerg us suillus whose diet consists of over 80% grass, had a digestibility coefficient of 87% on an all grass diet. All species had similar coeff icients of digestibility of > 90% when fed on a uniform diet of sweet potato. Bulbs and corms had a low fibre content (3.3-4%), high calorif ic value (15-16 kJ/g) and high digestibility coefficients (95.7-96%) a nd on this diet the mole-rats maintained their body mass. Food of lowe r digestibility tended to have a high fibre content(8.2-45%) and, with the exception of B. suillus, although the mole-rats consumed a greate r quantity of food, they lost mass. The sweet potato had a low fibre c ontent(4.1%) but was energetically very similar to bulbs and corms (15 .5 kJ/g). Geophytes which have low fibre contents are generally small (1-20 g), whereas geophytes with high fibre contents are much larger ( 30-2000 g) and often occur in more arid zones.