Preileal digestibility of coconut fat and soybean oil in horses and their influence on metabolites of microbial origin of the proximal digestive tract.

Three horses (approximately 190 kg BW) fitted with a permanent fistula at the end of the jejunum were used. To a control diet (1/3 hay, 2/3 mixed feed) one of two fat types (coconut fat or soybean oil) were added at 2 levels resulting in fat intakes of 0.1 g (control diet) to 0.5 or 1 g/kg BW 0.5 d, respectively. Each experimental period consisted of 2 weeks adaptation, 2 days of breath tests (before and hourly after the morning meal) and 5 days sampling of chyme. Crude fat, crude protein, concentrations of organic acids (SCFA, lactic acid), pH, and the minerals calcium, magnesium and phosphorus were determined in the chyme; H2 and CH4 in the expired air. The following results were obtained: 1) Fat feeding significantly (P < 0.01) stimulated (independent of amount or kind of fat) the jejunoileal flow of chyme. 2) Preileal fat digestibility increased significantly (P < 0.01) from 30-38% during the control periods to 73-80% (moderate fat intake) and 82-86% (high fat intake). Differences between the fat sources were not significant. 3) Fat addition resulted dose dependent in a reduction (P < 0.05) of lactic acid as well as SCFA concentrations of chyme (at 5th h postprandial). 4) Fat intake caused a reduction in the H2-concentration of the exhaled air (P < 0.05). Such effect was not found with the CH4-concentration, except the high soybean oil level which tended to reduce the concentration. 5) The addition of fat had no significant effects on preileal net absorption of magnesium and calcium, whilst the net secretion of phosphorus significantly increased (P < 0.01). 6) The preileal protein digestibility (control periods 48-53%) was slightly decreased (P < 0.05), due to the fat inclusion.