Digestibility of timothy hay by African elephants

Digestion studies in captive Hippopotamidae: a group of large ungulates with an unusually low metabolic rate

We performed intake and digestibility studies in four common (Hippopotamus amphibius) and four pygmy (Hexaprotodon liberiensis) hippos from two zoological institutions, using acid detergent lignin as an internal marker for the quantification of faecal output. In the case of one pygmy hippo, where total faecal collection was also possible, there was no distinct difference between the two methods of faecal output quantification. Two animals from each species were tested on a conventional zoo diet of hay and concentrates (diet HC) and on hay only (diet H). The other two animals received fresh grass at two different levels of intake (diets G1 and G2). Dry matter (DM) intake was higher on HC than on H or G diets, and averaged 37 +/- 11 for common and 35 +/- 14 g/kg(0.75) for pygmy hippos. There were no species differences in the average digestibility (aD) coefficients. Non-dietary faecal nitrogen averaged 65 +/- 4% of total faecal nitrogen, aD of crude protein (CP) averaged 67 +/- 9% and true protein digestibility 89 +/- 3%. Average digestibility of DM and crude fibre averaged 54 +/- 11% and 45 +/- 17%, respectively. In comparison with ruminants, hippos generally achieve lower aD for DM, organic matter and fibre parameters, but equal or higher aD CP coefficients. This is most likely due to the absence of significant fermentative activity in the hindgut and the corresponding low metabolic faecal nitrogen losses. Digestible energy intake was higher on HC than on H or G diets and averaged 0.30 +/- 0.11 MJ/kg(0.75) metabolic body mass. This value is extremely low for ungulates, supporting earlier suspicions that hippos have particularly low metabolic rates, and explains the proneness of this species to obesity in captivity when fed energy-dense pelleted feeds.

Studies on feed digestibilities in captive Asian elephants (Elephas maximus)

In order to test the suitability of the horse as a nutritional model for elephants, digestibility studies were performed with six captive Asian elephants on six different dietary regimes, using the double marker method with acid detergent lignin as an internal and chromium oxide as an external digestibility marker. Elephants resembled horses in the way dietary supplements and dietary crude fibre content influenced digestibility, in calcium absorption parameters and in faecal volatile fatty acid composition. However, the absolute digestibility coefficients achieved for all nutrients are distinctively lower in elephants. This is because of much faster ingesta passage rates reported for elephants. No answer is given to why elephants do not make use of their high digestive potential theoretically provided by their immense body weight. Differences in volatile fatty acid concentrations between these captive elephants and those reported from elephants from the wild are in accord with a reported high dependence of free-ranging elephants on browse forage.