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

Abstract

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.

Resource partitioning among African savanna herbivores in North Cameroon: the importance of diet composition, food quality and body mass

“…In both the dry and the wet season, nitrogen and phosphorus concentrations of hippopotamus faeces were much lower than of the other species. In contrast to antelopes and buffalo (family Bovidae), hippopotamus is a non-ruminating foregut fermenter, and its digestive physiology is characterized by relatively long gut retention times and low dry matter digestibility compared with ruminants (Clauss et al 2004, Schwarm et al 2006. Bacterial fermentation in the very short hindgut of the hippo is low compared to ruminants (Schwarm et al 2003(Schwarm et al , 2006 and the lower nitrogen concentrations in hippo faeces thus most likely reflect low losses of bacterial protein rather than a general body mass-diet quality relationship.…”

“…In contrast to antelopes and buffalo (family Bovidae), hippopotamus is a non-ruminating foregut fermenter, and its digestive physiology is characterized by relatively long gut retention times and low dry matter digestibility compared with ruminants (Clauss et al 2004, Schwarm et al 2006. Bacterial fermentation in the very short hindgut of the hippo is low compared to ruminants (Schwarm et al 2003(Schwarm et al , 2006 and the lower nitrogen concentrations in hippo faeces thus most likely reflect low losses of bacterial protein rather than a general body mass-diet quality relationship. Although various studies have argued that fibre digestion increases with body mass (Gordon & Illius 1994, 1996Iason & Van Wieren 1999, Illius & Gordon 1992, Robbins et al 1995, we could find no clear relation between fibre concentrations and body mass.…”

Carnivorous mammals: nutrient digestibility and energy evaluation

“…If the energy content of a currently fed diet could be estimated with sufficient accuracy, it would therefore allow an estimation of the animal's maintenance energy requirement [e.g. Schwarm et al, 2006]. Finally, in budgeting the costs of feeds, it is necessary to compare feeds not on a wet weight basis, but rather on either a dry weight basis [Watkins, 1985] or ideally on an energy basis; the latter is only possible if adequate methods for the estimation of energy exist.…”

Comparative digestion studies in wild suids at Rotterdam Zoo

“…This is most likely owing to the fact that ruminants, like both babirusa and peccaries, do not only have a forestomach compartment but also a site of bacterial fermentation in the hindgut, from which bacterial matter will be lost in the feces. Only for a foregut fermenter without a fermentation site in the hindgut, such as the hippopotamus, should higher apparent protein digestibilities (owing to lower metabolic fecal losses in the form of excreted bacterial protein) be expected [Schwarm et al, 2006].…”