Fluid and particle retention in captive okapi (Okapia johnstoni)

Area of Science:

• Animal Science
• Digestive Physiology
• Ruminant Nutrition

Background:

• Food retention time is crucial for understanding herbivore digestive strategies.
• The okapi, a browsing ruminant, has a unique digestive physiology that warrants investigation.
• Comparing okapi digestive efficiency to other ruminants can reveal adaptations to specific diets.

Purpose of the Study:

• To quantify the mean retention time (MRT) of fluid and particle phases in the okapi's gastrointestinal tract (GIT) and reticulorumen (RR).
• To compare the okapi's digestive efficiency, specifically its particle-to-fluid retention time quotient, with other ruminant species.
• To elucidate the okapi's digestive strategy in relation to its natural browse diet.

Main Methods:

• Four captive okapi specimens were used to measure retention times.
• Co-EDTA (fluid phase) and Cr-mordanted fibres (particle phase) were employed as pulse-fed markers.
• Fecal excretion of markers was monitored over 10 days, and various models were applied to calculate retention times.

Main Results:

• Average MRT(particle)GIT was 47±8 h and MRT(fluid)GIT was 36±5 h.
• Average MRT(particle)RR was 27±7 h and MRT(fluid)RR was 17±4 h.
• The okapi exhibited lower MRT(particle)/MRT(fluid) quotients (1.3±0.1 for GIT, 1.6±0.2 for RR) compared to species like cattle and sheep.

Conclusions:

• The okapi possesses a less developed fiber retention mechanism compared to other ruminants.
• This adaptation is likely linked to a higher fermentation rate and lower digestibility of their natural browse diet.
• Okapi digestive strategy is optimized for processing browse, differing significantly from grass-grazing ruminants.