Challenges in the Definition and Measurement of Subacute Ruminal Acidosis in Holstein Dairy Cows: A Review

Subacute ruminal acidosis can be defined as a depression of rumen pH, which affects animal health and production. Although researchers have tried to find a solution for this disorder, it is a prevalent problem that causes considerable losses in commercial dairy cow production. This review aims to reveal critical points in current knowledge about subacute ruminal acidosis and suggest solutions for future research. The first challenging issue in subacute ruminal acidosis is the diagnosis method of this disorder, which requires appropriate statistical evaluation and modeling. In addition, biological factors should be considered to define subacute ruminal acidosis since some roles have recently been observed for different CO2 species in the rumen as a direct cause of the events. These CO2 species are sometimes more accurate than rumen pH in explaining the decrease in feed intake, milk yield, milk fat percentage, and inflammation responses. In the future, the measuring of the CO2 species in the rumen may be a replacement for pH measurement or become a factor that can greatly explain ruminal acidosis. Compared to basic methods, another challenging point is the reliability of rumen pH measurements as well as the accuracy of newly developed sensors. The reticular pH with current boluses could be measured by monitoring cows on-farm or a large number of animals in research. In conclusion, a thorough definition and precise application of new measurement devices can reveal some unknown factors for subacute ruminal acidosis in dairy cows.