The effect of extrusion cooking of different starch sources on the in vitro and in vivo digestibility in growing pigs

A study with a total of 36 crossbred castrate male pigs (37.5 ± 0.6 kg) fitted with a simple T-cannula was carried out. The effect of extrusion cooking of barley, peas and a mixture (4:1) of potato starch and wheat bran (PSWB) on the coefficients of ileal (CIAD) and total tract apparent digestibility (CTTAD) according to a 3×2 factorial design was determined. The starch digestion profile of carbohydrate-containing ingredients was described using an in vitro setup based on the Englyst procedure for nutritional classification of starch. Extrusion cooking increased the proportion of rapidly digestible starch (RDS), and reduced the proportion of slowly digestible starch (SDS) and resistant starch (RS), and an in vitro digestion profile up to 8 h demonstrated major differences in the rate and extent of digestion of the raw carbohydrate sources, while the digestion profiles of the extruded products were almost identical.In vivo, extrusion cooking caused a big increase in the CIAD of starch and total carbohydrates of the diets containing legume and root starches; for PSWB, the CIAD of starch increased from 0.32–0.47 to 0.98, and for peas the CIAD of starch increased from 0.80 to 0.91 when the starch containing ingredient was extruded. The difference in CIAD between raw (0.93) and extruded barley (0.99) was not significant. Whereas extrusion cooking had a strong influence on the CIAD of crude protein with the barley and pea diets, only marginal effects were seen for the PSWB diets, where most protein was in the form of added casein. Extrusion cooking increased significantly the CTTAD of dry matter, organic matter and crude protein of the pea and PSWB diets, but not of barley. Overall, the experiment reported shows that the effect of extrusion cooking on nutritional value and amounts of substrate entering the large intestine using carbohydrate-rich feedstuffs for growing pigs is dependent on carbohydrate source.