The impact of reducing dietary crude protein and increasing total dietary fiber on hindgut fermentation, the methanogen community and gas emission in growing pigs

Sixty-four cross bred 6 week-old intact male pigs (initial BW = 13.8 ± 2.3 kg) were randomly distributed to 4 separated modules using a three-phase feeding program in which two dietary crude protein (CP) and total dietary fiber (TDF) levels were tested in a 2 × 2 factorial arrangement under a commercial-like production system. The room air was sampled and analyzed for NH3 and CH4 while the slurry pit air was sampled and analyzed for CH4 content during the early growing (phase I, 13.8-38.6 kg of body-weight), growing (phase II, 38.6-72.8 kg of body-weight) and finishing periods (phase III, 72.8-108.7 kg of body-weight); at the end of the finishing phase, 16 random pigs were sacrificed and cecum and colon contents were sampled to determine fermentation and microbial parameters. The pH and ammonium content increased with digesta transit being lower in cecum (6.0 and 69.7 mg/L) than in colon (6.3 and 156.3 mg/L) whereas the opposite trend was seen for total VFA and acetate (175.2 mM and 62.6 mol/100 mol vs. 141.1 mM and 57.2 mol/100 mol, respectively; P < 0.05). Low protein (LP) and high fiber (HF) diets showed a higher NH3 concentration in the colon but not in cecum samples. Dietary fiber also altered intestinal VFA concentration where animals fed Low fiber (LF) diet showed high VFA's concentrations and such effect was more pronounced in colon samples. Total NH3 (1.8, 4.8 and 8.5 g/day) and methane (2.5, 3.5 and 7.5 g/day for Phase I, II and III, respectively) emissions increased consistently with age (P < 0.05), dietary CP level increased NH3 volatilization (6.3 vs. 3.8 g/d for high protein (HP) and LP diets respectively; P < 0.01) and fiber tended to increase methane emission (5.0 vs. 4.0 for HF and LF diets, respectively P < 0.1). The methane production measured at slurry pit contributed significantly to total CH4 emission (3.26, 9.02 and 16.91% in the phases I, II and III respectively). Dietary CP increased total bacteria (TB; 9.7 vs. 9.5; P < 0.03) and total methanogenic archaea (TMA; 7.2 vs. 6.4; P < 0.01) abundances in the intestinal as well as the slurry (6.8 vs. 6.3 Log n° copy/ g fresh matter (FM); P < 0.01) samples whereas TDF did not alter microbial titers. Differences in CH4 emission did not reflect the TMA concentration in hindgut contents.