Effect of Particle Size of Wheat and Barley Grain on the Digestibility and Fermentation of Carbohydrates in the Small and Large Intestines of Growing Pigs

SIMPLE SUMMARY: The price of feed ingredients has been drastically increasing over the last decade, and thus the methods for improving nutrient digestibility and utilization with various feed ingredients have been widely studied in the field of the swine industry. One of the most efficacious approaches to enhancing nutrient digestibility and utilization is the manipulation of feed particle size. Nonetheless, limited research has been conducted on the impact of varying particle sizes of feeds with high fiber content. Dietary fiber is composed of several components, including β-glucan, arabinoxylan, and cellulose, which exhibit distinct physiological effects on the small and large intestines. The compositions and proportions of these components can influence and modulate nutrient digestibility in the small and large intestines of pigs. The objective of the present investigation was to examine the potential for enhanced nutrient and fiber digestibility in growing pigs through the reduction of particle size in barley and wheat diets. Similar ileal and total nutrient digestibility were observed in pigs fed diets containing fine and coarse wheat; however, pigs consuming coarse barley exhibited reduced nutrient digestibility compared to the other diets. Consequently, the present study shows that nutrient digestibility was more influenced by reduced particle size in barley than wheat, most likely because of the rigid fiber structure of barley and barley hull. ABSTRACT: The objective of this investigation was to study the effects of different cereal types, barley and wheat, with different particle sizes (PS) on the recovery of ileal digesta and fecal excretion, digestion of nutrients and fiber components, mean transit time (MTT), and short-chain fatty acid content and composition in growing pigs studied in two experiments. Five barrows with ileal cannulas (initial BW 35.9 ± 1.5 kg) in Experiment 1 and thirty-two castrated pigs (30.8 ± 1.3 kg) in Experiment 2 were fed four different diets: barley fine, barley coarse, wheat fine and wheat coarse diets. The cereal type and PS did not influence the relative weight of the small and large intestines and pH of digesta, whereas MTT in the large intestine of pigs fed the coarse barley diet was lower compared to pigs fed other diets (p < 0.05). Pigs fed the coarse barley diet had lower apparent ileal digestibility (AID) and apparent total tract digestibility (ATTD) of nutrients and fiber (p < 0.05), whereas pigs fed the fine barley diet had similar AID and ATTD to pigs fed wheat fine and coarse diets (p < 0.05). In conclusion, the barley diet was more influenced by PS in comparison to wheat, thereby inducing lower AID and ATTD of nutrient.