<i>In vitro</i> digested ingredients as substitute for ileal digesta in assessing protein fermentation potential in growing pigs

Understanding protein fermentation in the hindgut of pigs is essential due to its implications for health, and ileal digesta is commonly used to study this process <i>in vitro</i>. This study aimed to assess the feasibility of utilising <i>in vitro</i> digested residues as a replacement for ileal digesta in evaluating the protein fermentation potential. <i>In vitro</i> residues from cottonseed meal, maize germ meal, peanut meal, rapeseed cake, rapeseed meal, soyabean meal and sunflower meal were analysed using a modified gas production (GP) technique and curve fitting model to determine their fermentation dynamics and compare with the use of ileal digesta. Significant variations were observed in GP parameters between <i>in vitro</i> digested residues, indicating differences in nitrogen utilisation by fecal microbiota. Soyabean meal and sunflower meal exhibited the highest maximum GP rates (R_max), with values of 29·5 ± 0·6 and 28·0 ± 1·2 ml/h, respectively, while maize germ meal showed slowest protein utilisation (17·3 ± 0·2 ml/h). A positive relationship was found between the R_max of <i>in vitro</i> residues and ileal digesta (R² = 0·85, <i>P</i> < 0·01). However, GP potential (GP_s) showed a tendency for a negative relationship (R² = 0·39, <i>P</i> < 0·1), likely due to narrow observed GP_s values and the presence of varied endogenous proteins in ileal digesta. Our results demonstrate the potential of using <i>in vitro</i> digested residues as a substitute for ileal digesta in assessing the fermentation potential of protein ingredients, particularly regarding the rate of protein fermentation.