Coprophagy in leporids and other mammalian herbivores

Abstract

Leporids have long been known to reingest soft faeces. However, it was recently found that they regularly reingest hard faeces, too. During the daytime, both soft and hard faeces are defecated and all of the faeces are reingested. Excreted at night are the hard faeces, which are normally discarded but reingested in starvation. The separation mechanism in the proximal colon, which diverts fine particles into the caecum and thus only passes large food particles, produces hard faeces. When the mechanism ceases acting, fermented caecal materials are excreted as soft faeces. The reingestion of soft faeces, rich in vitamins and microbial proteins, is physiologically imperative. Hard faeces are basically a refuse, but their thorough mastication at reingestion reduces poorly digestible large particles to fine ones good for fermentation. The regular reingestion of daytime hard faeces thus promotes food digestibility. The temporary use of night-time hard faeces allows leporids to do without food for some time. It thus gives leporids behavioural flexibility and thereby an ecological advantage. Reingestion is also known in other small-to medium-sized herbivores, which are all caecal fermenters. Morphological differentiation between faeces is reported only in larger species, but all ingested faeces are found to be richer in nutrients than discarded ones. Thus a separation mechanism is probably present in all reingesting species. Reingestion activity is deeply related to other behavioural and physiological traits of small mammalian herbivores, hence its study is important to understanding of their ecology and biology. Leporids are the largest of the reingesting species except for the semi-aquatic Coypu, and reingestion by leporids is certainly the most sophisticated. This development of a reingestion-involved digestive system has probably brought them to their present niche, as terrestrial medium-sized generalist mammalian herbivores, and consequently made their characteristic hide-and-run lifeforms by exposing them to a strong predation pressure.

Digestive strategies in two sympatrically occurring lagomorphs

“…Re-ingestion of the caecum contents is an important source of nitrogen for herbivores (Garcia, De Blas et al, 1995;Takahashi & Sakaguchi, 1998;Iason & Van Wieren, 1999;Hirakawa, 2001). The importance of re-ingestion for the digestion of nitrogen was illustrated by a 10% reduction of the crude protein and nitrogen digestibility in rabbits that were deprived of caecotrophy (Grigorov, 1989).…”

“…This results in the production of two types of faeces; hard faeces that mainly consist of poorly digestible food particles and soft faeces composed of the material retained and fermented in the caecum. These soft faeces are normally re-ingested after excretion (caecotrophy), to make use of the end products of fermentation and the microbial proteins present in the soft faeces (Hirakawa, 2001).…”

“…Although caecotrophy is a common phenomenon in leporids (Hirakawa, 2001), several studies suggest a difference in the digestive system between rabbits Oryctolagus spp. and hares Lepus spp.…”

“…First, the type of soft faeces that is produced is different. Rabbits produce soft faeces with a tough surface membrane, whereas hares produce amorphous soft faeces without a membrane (Hirakawa, 2001). The faeces with a surface membrane remain intact in the stomach for several hours after reingestion.…”

“…As re-ingestion of the caecum contents is an important source of proteins for herbivores (Iason & Van Wieren, 1999;Hirakawa, 2001), we hypothesized that rabbits have a higher nitrogen digestibility, especially when diets contain high levels of fibres. We tested this by comparing the digestive efficiency of rabbits O. cunniculus and European brown hares L. europaeus in a feeding trial using diets with increasing fibre contents.…”