Digestive Processing in a Herbivorous Freshwater Turtle: Consequences of Small-Intestine Fermentation

Abstract

The Florida red-bellied turtle, Pseudemys nelsoni, on a diet of the aquatic plant Hydrilla verticillata, has high digestive efficiencies for dry matter, organic matter, energy, and cell walls, and moderate digestive efficiency for nitrogen. High cell wall digestibilities are a result of microbial fermentation in both the small and large intestines. Digestibilities are higher than most values reported for herbivorous reptiles on foliage diets. Mass-specific intake falls within the range measured in freefeeding herbivorous reptiles. Fermentation in the small intestine has not been reported previously in reptiles. Endproducts of fermentation-volatile fatty acids (VFAs) and gases-and concentration and rate of production of VFAs are similar to those in other herbivores. Fermentation in the small intestine has important nutritional consequences, such as a competition between endogenous enzymes and gut microflora for the highly nutritious, soluble substrate in the digesta of the small intestine. Energy from VFAs produced by the microbial fermentation approximates the total daily energy gain to P. nelsoni on a hydrilla diet. One might havepredicted, based on the large ratio ofsmall intestine length to large intestine length, that P. nelsoni would not have relied on fermentation. The shift of fermentation into the small intestine demonstrates that, at least in P. nelsoni, digestive strategy is not constrained by gut morphology.