Influence of fiber on ileal and total tract digestibility of nutrients, the degradation of non-starch polysaccharides, and enteric methane production in growing pigs and gestating sows

There is an urgent need to develop feeding strategies to reduce greenhouse gas emissions from pigs in order to reduce the climate impact of the pork industry. This study aimed to examine the effects of dietary soluble and insoluble total fiber (TF) sources on enteric methane (CH₄) production, nutrient digestibility, and the degradation of non-starch polysaccharides (NSP) in growing pigs and gestating sows. A total of six ileal-cannulated growing pigs and six ileal-cannulated gestating sows were allocated to one of the three experimental diets according to a repeated 3 × 3 Latin square design. Dietary treatments consisted of a control diet (CON) based on wheat, barley, and soybean meal (188 g TF/kg dry matter (DM)) and two high-fiber diets where sugar beet pulp (SBP) and wheat bran (WB) were added to the CON diet as a partial substitution of wheat and barley on a DM basis to supply soluble or insoluble TF, respectively. The amount of feed provided to the growing pigs and gestating sows varied between diets to supply similar daily amounts of metabolizable energy. The animals were placed in metabolic cages for 7 days to determine nutrient digestibility after a 7-day dietary adaptation period. During the experiment, animals in metabolic cages were placed in open-air circuit respiration chambers for 2 times 24 hours to quantify the gas exchange. Feeding growing pigs and gestating sows with the WB diet significantly decreased the apparent total tract digestibility of DM, organic matter, calculated TF, NSP, and gross energy compared to the CON and SBP diets. The experimental diets did not influence the amount of NSP passing the ileum and NSP fermentation in growing pigs. Feeding WB and SBP diets increased the amount of NSP fermented in the gastrointestinal tract of growing pigs and gestating sows compared to the CON diet. Compared to the CON and SBP diets, the inclusion of WB increased the fecal excretion of NSP in gestating sows and growing pigs. Feeding WB to gestating sows and growing pigs numerically increased daily enteric CH₄ production by 25 % and 31 %, respectively, compared to the CON diet. In contrast, feeding sows and growing pigs an SBP diet increased daily enteric CH₄ production by 90 % and 116 %, respectively, compared to the CON diet (P<0.001 and P=0.008, respectively). The enteric CH₄ production of gestating sows fed WB diet decreased significantly compared to the CON diet when enteric CH₄ production was expressed either as CH₄ production per g fermented NSP or per g of NSP intake (P=0.021 and P<0.001, respectively). In conclusion, enteric CH₄ production was affected by the TF source and physiological stage of the pigs. Therefore, these factors must be considered when developing feeding strategies to reduce greenhouse gas emissions from pigs.