Influence of maize particle size on the kinetics of starch digestion in the small intestine of growing pigs

The kinetics of starch digestion in the small intestine, nutrient utilisation and the performance of growing pigs that were fed diets containing maize of different particle sizes were evaluated. For the performance evaluation, 42 barrows and females (initial weight: 30.5 +/- 1.78 kg) were used in a randomised block design with three treatments [maize with different geometric mean diameters (GMD) of 550, 700 and 850 m] and seven replications. To evaluate the kinetics of starch digestion, one animal from each experimental trial was sacrificed. The small intestine was removed and separated into five equal parts. The starch digestibility in each segment was determined. To determine the total digestibility and nitrogen balance, 24 barrows (initial weight: 41.3 +/- 4.72 kg) were housed in metabolism cages in a randomised block design with three treatments and eight repetitions. The animals that were fed diets containing maize of 550-m GMD exhibited better (P = 0.008) feed conversion. However, the digestion of starch was gradual and variable among the degrees of grinding that were tested. There were higher (P = 0.008; 0.005 and 0.009) digestible energy, dry matter digestibility and nitrogen uptake in diets containing the maize ground to 550 and 700 m in GMD. Thus, the smallest GMD of maize (550 m) that was used in diets for growing pigs improves feed conversion. GMD of 550, 700 and 850 m of maize were associated with rapid, intermediate and slow starch digestion, respectively.