C. Meienberger et al., FOOD-INTAKE RATE AND BODY-MASS INFLUENCE TRANSIT-TIME AND DIGESTIBILITY IN THE DESERT TORTOISE (XEROBATES-AGASSIZII), Physiological zoology, 66(5), 1993, pp. 847-862
Studies of digesta transit in the desert tortoise (Xerobates agassizii
, formerly Gopherus agassizii) voluntarily eating a succulent diet (gr
een, growing Erodium cicutarium, red-stemmed filaree) or a dry diet (d
ead Schismus barbatus, split grass), indicated that digesta flow was d
etermined primarily by a gut-fill effect Total food consumed between t
he times of marker ingestion and marker excretion remained constant fo
r a given diet, regardless of feeding rate, and was related allometric
ally to body mass (exponent = 0.707). Higher feeding rates and their c
orrespondingly shorter transit times occasioned lower digestibilities
of dry matter, gross energy, and cell-wall components. The gastrointes
tinal tracts of tortoises eating green E. cicutarium contained nearly
three times as much dry matter as when the tortoises were eating dry S
. barbatus. This difference in gut fill may be related to the differen
t physical (structural) properties of green and dry plant parts. Gravi
d females had a reduced gut fill, presumably because eggs in the ovidu
ct reduce the potential gut volume. Unfortunately, insufficient data w
ere obtained for gravid females (n = 3) to allow formulation of a pred
ictive equation for food intake and transit time in females carrying e
ggs.