Characterizing Intraruminal Differences of the pH and Fermentation in Cattle.

This study characterized the association between the ventral and dorsal ruminal pH in cows. The experiment was conducted with six nonlactating rumen-cannulated Holstein cows fed either a grain-rich diet (65% concentrate in dry matter) or a forage-only diet. The dorsal and ventral ruminal pHs were measured in each cow using two identical indwelling systems, which recorded pH every 5 min. Furthermore, the volatile fatty acid concentrations and osmolality were determined in free ruminal liquid (FRL) of the ventral rumen and dorsal mat particle-associated ruminal liquid (PARL) and in feces. Precision and accuracy properties of dorsal ruminal pH and ventral ruminal pH as a measure of reproducibility were statistically evaluated. Data showed that the concordance correlation coefficient, representing the strength of the relationship between the ventral and dorsal ruminal pHs, was high when feeding the grain-rich diet (0.857), but low when feeding the forage-based diet (0.467), with accuracy of 0.917 and 0.525, and precision 0.935 and 0.890 for grain-rich diet and forage-based diet, respectively. The study established a relationship between ventral and dorsal ruminal pHs showing that ventral pH can serve as a proxy for dorsal pH, though this relationship demonstrated higher reproducibility only when feeding grain-rich diets.