Fluid and particle retention in captive okapi (Okapia johnstoni)

Abstract

Retention time of food in the digestive tract is among the key variables that describe the digestive strategy of a herbivore. Mean retention time (MRT) was measured on 4 captive specimens of the okapi, a strictly browsing ruminant. Retention time was quantified on different diets, using Co-EDTA (fluid phase) and Cr-mordanted fibres (1-2 mm) (particle phase) as pulse-fed markers. Average food intake was 55-65 g DM/(kg BW0.75*d). Fecal excretion of the markers was quantified over 10 days. Different models to calculate retention time and passage rate in the gastrointestinal tract (GIT) and the reticulorumen (RR) were applied. Average MRT(particle)GIT was quantified to be 47+/-8 h and MRT(fluid)GIT 36+/-5 h. Concerning estimation of retention times in the reticulorumen, MRT(particle)RR was quantified to be 27+/-7 h, while MRT(fluid)RR was 17+/-4 h. The quotients MRT(particle)/MRT(fluid) were quantified to be 1.3+/-0.1 for the GIT and 1.6+/-0.2 for the RR. Compared to data established with comparable markers, the okapi has low coefficients of MRT(particle)/MRT(fluid). A less well developed retention mechanism for fibres compared to species like cattle or sheep can be explained by a comparatively high fermentation rate and low digestibility of the natural food of the okapi-browse-in comparison to grass.