Effect of different feeding regimes on cecotrophy behavior and retention of solute and particle markers in the digestive tract of paca (Cuniculus paca).

Many small herbivores practice cecotrophy - the ingestion of special feces enriched in microbial protein by colonic separation mechanisms (CSM). In digesta passage experiments, secondary marker excretion peaks in feces are considered indicative of marker-reingestion via cecotrophy, but corroboration by behavioral observation was lacking so far. The paca (Cuniculus paca), a Neotropical hystricomorph rodent, produces two different kinds of feces (hard and soft) and practices cecotrophy either directly (from the anus) or indirectly (from a pile of defecated feces, mostly when hard and soft feces are defecated together). To investigate effects of diet on cecotrophy, we monitored cecotrophy behavior and digesta passage marker excretion of solute and particle markers in four adult pacas, at constant food intake, on four diets varying in protein and fiber content. Marker excretion patterns suggested a 'mucus-trap' CSM typical for hystricomorph rodents, and showed secondary peaks of a similar time lag after cecotrophy as the primary marker peak after marker feeding. However, not every cecotrophy event was followed by a secondary marker peak. On higher fiber/lower protein diets, the number of cecotrophy bouts, the duration of cecotrophy, the number of secondary marker peaks and the difference between solute and particle marker retention increased, whereas the proportion of indirect cecotrophy decreased, indicating a higher degree of digesta phase separation on these diets. Compared to hard feces, soft feces were particularly enriched in solute marker concentration. Cecotrophy depends on a CSM that varies in its efficiency with the nutrient composition of the diet.

Direct and indirect caecotrophy behaviour in paca (Cuniculus paca).

The colonic separation mechanism in lagomorphs and some rodents, associated with caecotrophy, serves to retain microbial protein. As tropical fruits have low protein concentrations, caecotrophy could be an important microbial protein source in frugivorous rodents such as the paca (Cuniculus paca). Due to conflicting reports on the occurrence of caecotrophy in this species, we obtained digestive tracts of three adult animals and observed the behaviour of four specimens maintained on a diet of a pelleted feed (P) and a supplemental mix of fruits and sweet potato (S, a source of structural fibre). In a Latin square design, P and S were both offered either in the morning (M) or in the afternoon (A), or with one item in the morning and the other in the afternoon (SP or PS). The paca's proximal colon is characterized by a distinct furrow typical for the colonic separation mechanism of hystricomorph rodents. Caecotrophy, both "direct" (from the anus) and "indirect" (from a pile of defecated faeces), was a regular component of the paca's behavioural repertoire, and caecotrophs contained more nitrogen and less fibre than hard faeces. Higher food intake led to less overall caecotrophy. With afternoon feeding of S, the onset of caecotrophy was delayed and the proportion of indirect caecotrophy increased, with hard faeces and caecotrophs often defecated together. No indirect caecotrophy occurred on treatment M. The results suggest that the time available after ingestion of structural fibre determines the efficiency of the colonic mechanism for the separation of hard faeces and caecotrophs.