Intrinsic grain starch digestibility affects the concentration of faecal markers of colonic fermentation and bodyweight gain without affecting feed intake in pigs

Abstract

The amount of energy available for metabolism from grain-based feeds determines pig growth rate. Available energy is influenced by feed intake (FI) and the relative extent of digestion in the small intestine (SI), compared with fermentation of undigested feed in the large intestine (LI). Milled and steam-flaked sorghum and wheat were used to evaluate the following hypotheses: 1) an increase in grain digestibility increases FI, decreases the extent of large-intestinal fermentation and improves the efficiency of feed use; and 2) faecal short-chain-fatty-acids (SCFA) and pH are indicators of the extent of grain fermentation in the LI. Apparent-amylase-diffusion-coefficients (ADC) were measured in vitro as an indicator of intrinsic starch digestibility. Pigs were fed ad libitum the four grain-based diets. FI, average-daily-weight-gain (ADG), feed-conversion-ratio (FCR, FI:ADG), faecal SCFA-concentration and pH were measured weekly. Linear models were fitted between: 1) ADC and ADG, FCR, SCFA-concentration, and pH; 2) ADG and SCFA-concentration, and pH; and 3) FCR and SCFA-concentration, and pH. Grain digestibility did not affect FI, but sorghum reduced ADG (14−21 day: P < 0.05; 7−28 day: P < 0.1) and increased FCR (7−14 day: P < 0.05; 14−21day: P = 0.001) compared to wheat. Sorghum produced more faecal SCFA than wheat at 7 day & 28 day (P < 0.1), and decreased faecal pH by 0.4 (14 day, 21 day & 28 day: P < 0.001). ADG and FCR were correlated with faecal SCFA and pH (P < 0.001 to 0.05). Low intrinsic starch digestibility increased fermentation in the hind-gut, with assumed loss of energy in heat, methane and voided microbes, resulting in less energy for metabolism. Providing pigs with cereal grains of high intrinsic digestibility should increase growth rate and efficiency of feed use without increasing feed intake.