Influence of the nature of carbohydrate intake on the absorption chronology of reducing sugars and volatile fatty acids in the pig.

The results of three successive experiments were compared in order to analyse the chronology of absorbed energy amounts resulting from enzymatic or microbial digestion, respectively. These experiments were undertaken in the pig to study the absorption kinetics of reducing sugars and amino-nitrogen formed during enzymatic digestion and of volatile fatty acids (VFA) formed through the action of the digestive flora. The animals were given well-balanced semi-synthetic diets containing poorly digestible or indigestible carbohydrates. These diets contained the following ingredients: (Experiment A) purified cellulose at two levels of incorporation (LC diet 6%, HC diet 16%); (Experiment B) alfalfa meal (22%) supplying 6% crude fibre (HA diet) versus lactose (22%) with an addition of 6% purified cellulose (HL diet); (Experiment C) sorbitol in the form of maltitol (53%) with an addition of 6% purified cellulose (SHyd diet) versus maltose under the same conditions (53%, SNat diet). Each diet was fed to five pigs fitted with catheters placed in the portal vein and carotid artery and with a flow probe around the portal vein, which made it possible to study the nutrient absorption after one meal (800 g). Under our experimental conditions (intake: 2 200-2 300 kcal, except HC 1 930 kcal) the higher level of crude fibre or the presence of osides in the diet which are poorly digestible in the small intestine (lactose, maltitol), depressed the absorption of reducing sugars (RS) (amount absorbed within 12 h relative to intake %: SNat 92.8; LC 82.7; HL 78.7; HA 76.0; HC 72.5; SHyd 71.3). The absorbed energy supply resulting from the VFA increased accordingly, in the presence of poorly digestible or indigestible carbohydrates (as a percentage of the total energy absorbed as RS, lactic acid (LA) and VFA: SNat 3.4; LC 7.1; HL 8.9; HC 10.4; SHyd 13.1) with one exception (HA: 6.0%). For all diets, the greatest energy absorption (42-63% according to the diet) occurred during the first 4 h after the meal, the larger fraction resulting from RS (86.8-94.8% according to the diet). The energy supply due to the absorption of VFA became large between the 5th and the 12th hour, and was larger for diets containing poorly digestible or indigestible carbohydrates (as a percentage of the total RS + LA + VFA: SNat 6.5; LC 8.7; HC 14.3; HC 14.4; SHyd 23.3) with one exception (HA: 9.0%). Although the late absorption of VFA was insufficient to compensate for the energy deficit due to a lower of RS, it may bridge the energy gap during the interprandial period.