Water absorption in relation to fermentation in the colon of the ostrich (Struthio camelus).

The colon is a major site for fermentation and water absorption in the ostrich. Water absorption along the colon was evaluated and its relationship to osmolality, Na+ concentration, short chain fatty acid (SCFA) concentration and carbohydrate content of digesta analysed. Mean water content decreased from 5.30 +/- 0.99 to 2.51 +/- 0.13 mf/g dry mass in the first 5 m of the colon. Correspondingly, mean carbohydrate content fell from 529.85 +/- 46.61 to 434.99 +/- 29.89 mg/g dry mass. A significant correlation was shown between the decreases in mean carbohydrate and water content along the colon (r2 = 0.997, P < 0.05). Changes in mean osmolality (+/- 10 mOsm/kg) and SCFA concentration (+/- 7 mmol/l) were minimal in comparison to the change in Na+ concentration (-54 mmol/l). These findings reflect a close coupling between SCFA production and absorption on the one hand and water absorption on the other.