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Twenty-Third Annual Meeting and Symposium of the
Desert Tortoise Council, April 3-5, 1998
Abstracts
Cattle, Dung and Tortoises: Symbiosis?
Mary E. Allen
National Zoological Park, Smithsonian Institution, 3001 Connecticut Avenue,
Washington DC 20008; and The Desert Tortoise Conservation Center, Las Vegas, NV 89117
Free-ranging desert tortoises will eat feces and other "non nutritive" materials. It has been postulated that tortoises in recent evolution have relied on cattle dung to maintain their populations when food resources were scarce. A scientific response to this hypothesis requires information on the nutritive properties of cattle feces, and specifically, on the ability of tortoises to extract nutrients from cattle feces. For a digestibility study, cattle dung was offered to 14 healthy juvenile tortoises (mass range 328-991 g) as the sole food during a one month adaptation period. Only four animals would eat a sufficient amount to be included in a subsequent four-week digestibility study. Samples of offered dung and all uneaten dung were collected and dried to determine dry matter (DM) intakes. All tortoise excreta were collected for nutritional analysis. During the third and fourth weeks of the trial, average DM intake was not significantly different from fecal excretion (mean difference = -0.44 ± 0.22 SE g/2wk), suggesting a net digestibility of zero. On a DM basis, dung samples contained 50.0 % ± 0.34 acid detergent fiber (ADF), 1.34 % ± 0.012 total nitrogen (TN), and 4.24 ± 0.542 kcal/g gross energy. These constituent levels did not differ significantly from those of uneaten dung. The estimated digestibility of energy and ADF were not significantly different from zero and the estimated TN digestibility was negative. Based on our preliminary trial results, the suggestion that tortoises have benefited from a symbiotic relationship with cattle and their feces is clearly speculative.
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