Evaluation of pea grains using coupled in vitro assays for precaecal digestion and hindgut fermentation in pigs

The nutrient composition of the pea grain fraction that escapes precaecal digestion may vary in response to the pea variant, affecting its fermentation characteristics in the hindgut. Quantifying the formation of fermentation end products in vivo remains challenging. Therefore, this study investigated the digestion and fermentation characteristics of 12 pea variants using two combined in vitro assays. In vitro indigestible solids (IVIS) of pea grains, representing the fraction of pea grains escaping precaecal digestion, were incubated for 48 h using a modified Hohenheim gas test with pig faeces as inoculum. Gas production was recorded at nine time points, and NH₄⁺-N and volatile fatty acids (VFA) were measured at 8 and 24 h. Precaecal disappearance was high for starch and crude protein ( >94%), whereas fibre fractions remained largely undigested ( <16%) and were the most abundant and variable fraction in the IVIS. Incubated IVIS differed in potential gas production and maximum rate of gas production among pea variants (p < 0.001, 46.7 to 73.9 mL/200 mg dry matter and 2.9 to 5.1 mL/h, respectively). For metabolite concentrations, an effect of the IVIS was observed for NH₄⁺-N and VFA at 8 and 24 h (p < 0.001). Multivariate regression showed a positive association of acid detergent fibre with the potential gas production (p < 0.001, R² = 0.82). The concentration of crude protein was positively associated with the NH₄⁺-N concentration at 8 and 24 h (p < 0.001, R² = 0.85, R² = 0.86). The crude fibre concentration was negatively associated with the branched-chain fatty acid concentration at 24 h (p = 0.001, R² = 0.70). Starch concentration was positively associated with gas production at 2 h (p < 0.016, R² = 0.49) and propionate concentration at 8 h (p < 0.038, R² = 0.86). To conclude, early-stage propionate production is driven by the precaecal indigestible starch, whereas the fermentation potential is primarily determined by the precaecal indigestible fibre fractions. Formation of metabolites by protein fermentation depends on the concentration of precaecal indigestible protein but may be inhibited with higher fibre concentrations. The differences in fermentation characteristics among IVIS of pea variants were associated with the analysed nutrient composition of the IVIS but not with those of the original grains.