High- or low-fibre diet, meal size and frequency: Effect on ileal and total tract digestibility and mean retention time in growing pigs

This study aimed to determine the effect of the size and frequency of meals and diet type (high- or low-fibre) on fibre degradation and retention time of digesta in growing pigs. Pigs (n = 6) were fitted with a T-cannula, and each received all treatments following a 2 × 3 factorial arrangement in a 6 × 6 Latin square experimental design. The diets were either corn-soybean meal-based diet with low fibre (LowFibre) or wheat-barley based diet with high fibre (HighFibre) and distributed differently: 2 meals per day that met 3 times the maintenance energy requirement (2 M), the same amount of feed in 8 meals (8 M), and 8 meals per day that met 5 times the requirements (8 M+). A diet type × meal interaction was observed for mean retention time (MRT) of the solid and liquid phase of digesta where MRT in LowFibre diet was higher in 2 M compared to 8 M and 8 M+ while in HighFibre only 8 M had lower MRT than 2 M and 8 M+ (Solid phase, P = 0.023, Liquid phase, P = 0.097). Ileum digesta from the LowFibre diet was less viscous than ileum digesta from HighFibre diet (P = 0.028) regardless of the meal distribution. Concentrations of the indigestible markers in the ileal digesta (TiO2 and YbCl3) increased faster in the LowFibre compared to the HighFiber diet, and marker concentrations were more constant in the 2 M than the 8 M and 8 M+ treatments (P < 0.05). Coefficient of apparent ileal digestibility (CAID) of dry matter, energy, crude protein, total non-starch polysaccharides (NSP) and insoluble NSP was higher in the HighFibre diet than the LowFibre diet, while opposed results were observed for apparent total tract digestibility (P < 0.05). No effect of meal type was observed on CAID. Blood glucose levels were stable throughout the day for 8 M and 8 M+ while blood glucose for 2 M was decreased between two meals (meal × time effect, P = 0.035). Larger meals in 2M-LowFibre, 2M-HighFibre and 8 M+HighFibre can therefore explain longer MRT potentially due to decreased motility and slower gastric emptying. In conclusion, feeding pigs with an increased number of meals per day allows a continuous flow of digesta, stabilized blood glucose and increased digestibility. Ingestion of a high-fibre diet causes increased digesta viscosity. The type of diet had more impact on digestibility and transit time than the meal size and frequency.