25th Annual Meeting and Symposium of the
Desert Tortoise Council, April 21-24, 2000
Abstracts

Digestible Energy in Foods of Juvenile Desert Tortoises

Danielle R. Shemanski, Lisa C. Hazard, Kenneth A. Nagy
Department of Organismic Biology, Ecology, and Evolution, University of California-Los Angeles, 90095-1606

The digestible dry matter and energy in two dietary grasses, Achnatherum hymenoides and Schismus barbatus, were measured in feeding trials on one to two year old desert tortoises. A. hymenoides (Indian ricegrass) is native to the Mojave Desert whereas S. barbatus (Mediterranean grass) is introduced. We offered weighed amounts of chopped dry grass of both species ad libitum to the tortoises (n = 10 for animals who ate A. hymenoides, and n = 6 for animals who ate S. barbatus), and collected uneaten food and feces daily for several weeks. Dry matter retained (food consumed minus feces produced) was used to estimate apparent dry matter digestibility. Energy content measurements of food and feces from microbomb calorimetry were combined with dry matter measurements to calculate apparent energy digestibility. Preliminary results suggest that energy digestibility is slightly lower than dry matter digestibility because feces have a slightly higher energy content (per gram) than food (probably due to bacteria in feces). Dry matter and energy digestibility's in juvenile Gopherus agassizii were roughly comparable to those determined in previous studies on adult desert tortoises (Meienberger et al. 1993, Nagy et al. 1998).

Literature Cited

Meienberger, C., I.R. Wallis, and K. A. Nagy. 1993. Food intake rate and body mass influence transit time and digestibility in the desert tortoise, Xerobates agassizii, Physiological Zoology 66:847-8.

Nagy, K.A., B. T. Henen, and D. B. Vyas. 1998. Nutritional quality of native and introduced food plants of wild desert tortoises. Journal of Herpetology 32:260-267.