Sites of Organic Acid Production and Patterns of Digesta Movement in the Gastrointestinal Tract of the Rock Hyrax

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Abstract
The rock hyrax, smallest of the present day ungulates and a near relative of the elephant, has a gastrointestinal tract of such complex nature that it may be considered comparable to both the simple and complex stomach mammals, and also to birds. They have a stomach to body weight capacity equal to that of sheep. But for all its complexity, the passage of ingesta is reasonably rapid. However, there are three major sites of digesta retention and microbial fermentation of the ingested material. The cranial stomach provides the first major site of fermentation with VFA levels comparable to those observed in the rumen (125–145 mM/liter). Quantities of lactic acid are also produced in the foregut where the pH may vary from 2 to 5.5. The ingested particulate material is exclusively retained in the cranial half of the stomach for 4 hours after consumption, and partially retained in the entire stomach for greater than 24 hours. The mid-gut sacculation provides the second major site of fermentation with the retention of the digesta in this gut segment for up to 16 hours. The two ceca provide the third site. Concentrations of VFA in these latter two gut segments approaches 80 mM/liter, while the near stable and neutral pH corresponds to the absence of lactic acid production.