Influence of dietary calcium and protein on fecal pH , consistency, and rate of passage in dairy cattle

Sixteen Holstein heifers and 20 calves were in trials on the effect of 10 and 15% crude protein and .3 and .9% calcium in the diet on fecal pH and consistency and on rate of passage of the liquid phase of digesta. Time of first appearance of polyethylene glycol was an indicator of rate of passage of the liquid phase in the lower tract of the animal. Respective fecal pH and standard errors for heifers and calves increased from 5.79 +/- .03 and 5.78 +/- .03 on low calcium diets to 6.24 +/- .03 and 6.33 +/- .03 on high calcium diets. High protein diets increased fecal pH from 5.89 +/- .03 and 5.97 +/- .03 to 6.13 +/- .03 and 6.14 +/- .03 for heifers and calves. Effects of calcium and protein were additive. Neither dietary protein nor calcium affected consistency of feces or first appearance of polyethylene glycol in feces. Mean first appearances of PEG in feces were 683 +/- 13 min for heifers and 528 +/- 18 min for calves. Small correlations between fecal pH and fecal consistency and between fecal pH and first appearance of polyethylene glycol in feces indicate little or no relationship of fecal pH to these two variables. From variance in the heifer trial, 10 fecal samples are required to estimate fecal pH within +/-.16 pH units with 95% confidence.