Modulating starch digestion kinetics via feed processing: Implications for growth and metabolism in weaned pigs

This study aimed to explore the effect of starch digestion kinetics on growth performance, serum biochemical indices, intestinal digestive function and protein deposition of weaned pigs. A total of 120 weaned pigs (Duroc × Landrace × Yorkshire, aged 35 d, weighted 9.00 ± 0.48 kg) were randomly divided into 3 treatments: corn, the main starch source (66.7%) of diets, was processed as ground, steam-flaked or extruded. The feed was offered as pellets. The trial lasted for 28 d. Extrusion and steam-flaking can accelerate the starch digestion rate, and diets with extruded corn significantly increased serum glucose concentrations at 1 and 2 h postprandial ( P ≤ 0.05). Compared with the ground corn treatment, the steam-flaked corn diet led to a significant decrease in the average daily feed intake (ADFI) of piglets from day 1 to 14 ( P = 0.009), and the extruded corn diet resulted in a reduction in average daily gain (ADG; P = 0.057) and ADFI ( P = 0.012) of piglets from day 15 to 28. Additionally, both the steam-flaked corn diet and the extruded corn diet significantly reduced the ADFI of piglets during day 1 to 28 compared with the ground corn diet ( P = 0.002). Moreover, lower serum albumin (ALB) concentration was observed in piglets fed the steam-flaked corn diet than those fed the ground corn diet on day 14 ( P = 0.005). The serum glucagon (GCG) concentration was higher ( P = 0.004) in piglets fed the ground corn diet than in those fed the steam-flaked corn diet or the extruded corn diet on day 28. In addition, on day 28, the concentration of ghrelin in the extruded corn group and the concentration of aspartate aminotransferase (AST) in the steam-flaked corn group were both increased ( P ≤ 0.05) compared with those in the ground corn group. Piglets fed the steam-flaked corn diet or the extruded corn diet had decreased ( P ≤ 0.05) activities of maltase and sucrase in the jejunal mucosa, down-regulated ( P ≤ 0.05) mRNA expression for sodium-dependent glucose transporter 1 ( SGLT1 ) and glucose transporter type 2 ( GLUT2 ) in the ileum, and increased apparent total tract digestibility (ATTD) of dry matter (DM), ether extract (EE), crude protein (CP), gross energy (GE) and starch on day 14 ( P ≤ 0.05). The ratio of villus height to crypt depth in the duodenum and ileum was increased in piglets fed the extruded corn diet compared with the ground corn diet ( P ≤ 0.05). Starch digestion kinetics had no marked effects ( P > 0.05) on expression of genes and proteins related to protein synthesis in longissimus thoracis. The results indicated that starch digestion kinetics can be effectively adjusted by feed processing, where piglets perform worse on diets with a rapid starch digestion. A relatively slow but continuous supply of glucose could spare amino acids from being catabolized in the intestinal mucosa, which may be better for piglet performance.