Fluid and particle retention in captive okapi (Okapia johnstoni)

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 MRTparticleGIT was quantified to be 47 ± 8 h and MRTfluidGIT 36 ± 5 h. Concerning estimation of retention times in the reticulorumen, MRTparticleRR was quantified to be 27 ± 7 h, while MRTfluidRR was 17 ± 4 h. The quotients MRTparticle/MRTfluid 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 MRTparticle/MRTfluid. 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.