Diversity and population density of methanogens in the large intestine of pigs fed diets of different energy levels

Marker gene analysis was performed to assess the effect of energy level on the diversity and population density of methanogens in pig fecal material. Crossbred pigs were fed high or low energy level diets, a high‐energy (HE) diet that satisfied daily gain at 1.2 kg, and a low‐energy (LE) diet with amount of 0.6 times of the HE diet. Growth performance and short‐chain fatty acid in feces were examined. Diversity of methanogen was analyzed by the α‐subunit of methyl coenzyme‐M reductase gene (mcrA) clone library from fecal DNA. The DNA copy numbers of mcrA were quantified by real‐time PCR. There was no difference in the concentration and composition of short‐chain fatty acid between treatments. Differences in the mcrA clone library were observed between HE and LE treatments (p < 0.05). Ninety‐five percent of cloned sequence affiliated genus Methanobrevibacter in the feces of the pig regardless of treatments. During the experimental period, no significant difference in the proportion of copy numbers of mcrA against that of 16S rRNA gene of total bacteria was observed between treatments. In conclusion, feeding energy level affected composition of methanogens in the large intestine of the pig, while population density of methanogen was not affected.