Changes in Ileum and Cecum Volatile Fatty Acids and Their Relationship with Microflora and Enteric Methane in Pigs Fed Different Fiber Levels

Mustard and grapeseed meals are low-cost by-products generated by the oil industry. We aimed to investigate the effects of fiber level on the concentration of volatile fatty acids (VFAs) in the ileum and cecum, as well as the microflora and enteric methane (E-CH 4 ) in pigs. A total of 70 Topigs hybrid pigs, 56 ± 3 days old, 20.96 ± 0.26 kg live weight, were randomly allotted to two feeding groups: (i) SM diet based on sunflower meal; (ii) MG diet based on mustard × grapeseed oil meals (MG-mixt). VFA profiles were determined by gas chromatography. E-CH 4 was calculated using our trial data along with prediction equations. The MG-mixt slightly decreased growth parameters but improved daily feed efficiency and gain cost. The MG diet increased the concentration of VFAs and the microflora level. The higher VFA level recorded in the cecum (+53.93%) was correlated with a lower pH level (Spearman correlation coefficient, rho = −0.529, p < 0.001). In relation to DM intake and energy retention, E-CH 4 recorded a highly significant decline in the MG group (<9.42%). A strong relationship was recorded among VFAs, microflora, predicted E-CH 4 , and fiber and NDF intake. The VFAs could be predictors for the E-CH 4 level ( p < 0.001). A significant relationship between E-CH 4 and total VFAs was noted (rho = −0.462, p = 0.04). We conclude that MG-mixt has the potential to replace sunflower meal, with the minor drawbacks being balanced by the advantages provided in terms of feed efficiency, E-CH 4 mitigation, and VFA levels.