Estimation of protein fermentation in the large intestine of pigs using a gas production technique

Proteolytic fermentation in the colon of pigs and the caecum of poultry can have negative effects on their performance and health due to formation of harmful end products. To reduce this, rations can be formulated with expected carbohydrate fermentation being higher in level, and rate, than that of protein fermentation, as it is accepted that available energy is the limiting factor during fermentation in the hindgut. In this study, a modified version of a gas production technique was used to determine fermentation characteristics of protein in feedstuffs and concentrates after pre-digestion with pepsin and pancreatic enzymes in order to simulate digestion in the stomach and small intestine of pigs. Completing the incubations in an N-free environment, and with an excess of rapidly fermentable carbohydrates, made N the limiting factor to microbial growth, and so gas production profiles reflect availability of N. Results showed that fermentation of protein in the hindgut can be determined with this modified gas production technique, and that there were distinct differences in protein fermentation among the feed samples. Availability of protein for fermentation was highest in pea meal, solvent extracted soybean meal and feather meal, and lowest in palm kernel (expeller), wheat grain and meat meal. Between 5 and 15 h of incubation, gas production increased linearly. Urea was used as a positive control, as it is readily available to microbes. Gas production after 10 h of incubation, relative to gas production with urea, was assumed to be a measure of protein availability, allowing the content and proportion of fermentable crude protein (CP) to be estimated. Results show that this gas production technique ranked feed samples relative to their CP availability in the hindgut. Four concentrates were made with increasing proportions of expected fermentable CP, which was confirmed with the in vitro technique.