Fiber digestibility by the orangutan (Pongo abelii): in vitro and in vivo.

Limited nutritional information exists on diets of free-ranging orangutans, Pongo abelii and P. pygmaeus. Although they are classified as frugivores, the chemical composition of their diet and their gastrointestinal anatomy suggest that they rely on fiber fermentation for a substantial portion of energy. However, the extent to which they can ferment fiber is not known. Continuous culture systems, inoculated with orangutan fecal bacteria, were established to determine the fiber-digesting capacity of orangutan hindgut microflora. The cultures received one of four treatments: soybean hulls, ground corncobs, corn starch, or no food. Neither dry matter nor neutral detergent fiber digestibilities differed significantly among treatments. However, neutral detergent fiber digestibilities were high for both the soybean hull (88.4%) and ground corncob (86.1%) treatments, indicating that the microflora had a strong fibrolytic capability. To determine whether the same fiber-degrading capacity occurred in vivo, two adult orangutans and one juvenile were fed four gel-matrix diets containing soybean hulls, ground corncobs, or ground primate biscuits. Neutral detergent fiber concentrations (dry matter basis) of the gel matrices were 52.9% with soybean hulls, 46.8% and 63.7% with ground corncobs, and 31.3% with ground primate biscuits. A fifth diet consisted of primate biscuits with 27.3% neutral detergent fiber (dry matter basis) and was considered the baseline diet. Neutral detergent fiber digestibility (74.5%) was greatest (P < 0.05) for the soybean hull gel diet and least (57.5% and 45.0%, respectively; P < 0.05) for the 63.7% neutral detergent fiber (dry matter basis) corncob gel diet and the baseline primate biscuit diet. Total volatile fatty acid concentrations in orangutan feces were not significantly different among diets; however, molar proportions of acetic, propionic, and butyric acid differed (P < 0.05) among diets. The results from both studies indicated that orangutans are capable of extensive fiber fermentation.

Fiber digestibility by black lemurs (Eulemur macaco macaco).

Black lemurs, Eulemur macaco, are classified as generalist feeders, consuming a proportion of fruits and leaves that varies with seasonal availability. It is hypothesized that black lemurs are capable of using neutral detergent fiber (NDF) as a source of energy through fiber fermentation in the cecum and large intestine. In captivity, they are typically fed a diet of commercially available primate biscuits and readily available produce, both of which are limited in NDE Digestibility trials were conducted on 14 black lemurs; 12 were housed in groups (four, three, three, and two) and 2 were individually housed. The lemurs were fed four manufactured feeds differing in fiber form and content. A commercially available primate biscuit, containing approximately 27% NDF, served as the control diet. The second diet contained the same primate biscuits, which were ground and then incorporated into a fiber-based gel matrix. The third and fourth diets were formulated using soybean hulls or ground corncobs as the fiber source, resulting in 53% and 47% NDF, respectively. Produce was added to the diet at 36% (dry matter basis). Dry matter digestibility differed significantly among all diets. Neutral detergent fiber digestibility was highest for the ground biscuit in gel and lowest for the two high-fiber gel diets, with biscuit digestibility values falling between the two extremes. The high-fiber gel diets were successful in increasing the NDF concentrations of the primate diets; however, black lemurs were capable of only limited fiber digestion.