A calibrated, glass-electrode pH meter (WTW pH 340-A; WTH Measurement Systems Inc., Ft. Myers, FL) was used to measure the pH of the fecal samples, which were diluted with deionized water at a ratio of 1:7.5 (wt/wt). One gram of the composite fecal sample from each pen was diluted with 9 mL of 1% peptone broth (Becton, Dickinson and Co.) and then homogenized