Expression of intestinal amino acid transporters, gut morphology, and amino acid digestibility in pigs fed proteins or free amino acids

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English. Dietary amino acids (AA) supplied as protein or in free form are digested and absorbed at different rates which can induce differences in gut physiology, like digestive and absorptive capacities, and metabolism. We compared the AA digestibility, expression of AA transporters, and gut morphology of pigs fed diets providing different forms of AA. Growing pigs (n = 30; 33.7 ± 4.1 kg) were fed one of the three experimental diets that provided AA as intact feather meal (INT), as free AA by extensive hydrolysis of feathers (HYD), or as synthetic AA with the same AA profile as HYD (FAA). Pigs were fed the same quantity of feed, energy, and AA. After 14 days, pigs were slaughtered 3 hours after feeding the experimental diet with indigestible markers. Digesta and tissue were collected from different sections of the small intestine. Jejunal digesta was used to measure AA digestibility as there was not enough ileal digesta during collection. Duodenum, jejunum, and ileum samples were analysed for expression of intestinal AA transporter genes and gut morphology. The AA digestibility from INT was lower compared to HYD and FAA (P < 0.05). Digestibility of Cys, Gly, Pro, and Thr was lower for FAA compared to HYD (P < 0.05). Crypt depth in the jejunum was lower (P < 0.01) and villi area in the ileum was higher (P < 0.05) for HYD suggesting greater surface for digestion and absorption. In the duodenum, INT expressed more PepT-1 (P < 0.01), while HYD expressed more CAT-1 (P = 0.04). Furthermore, HYD expressed more ASCT2 (P = 0.02) and CAT-1 (P = 0.04) in the jejunum compared to other treatments. The expression of these transporters along the intestine depended on the relative abundance of dietary absorbable AA. Results showed that the dietary AA form influences the expression of different AA transporters and morphology of the small intestine, which can impact AA absorption and bioavailability for peripheral tissues.