After the fermentation, a gas sampling pump (Model GV-100; Gastec Corp., Avase, Japan) was utilized for gas
detection (Gastec detector tube No. 3La for NH3, and No. 4LK for H2S; Gastec Corp.) Before measurement, the fecal samples were manually shaken for approximately 30 s to disrupt any crust for-mation, and to homogenize the samples, and then 100 mL of the headspace air was sampled from approximately 2.0 cm above the sample.