Individual Variability in Susceptibility to the Occurrence of Low Rumen pH in Lactating Dairy Cows: What Has Been Done and What Needs to be Done

Individual variability in susceptibility to low rumen pH is one of the currently known aspects of rumen aci-dosis in dairy cows, and its understanding and management may address part of the complications of rumen acidosis. This review aims to summarize the outputs of current findings on individual variability in suscep-tibility to low rumen pH in terms of causes and effects and to provide strategies to manage it in research and commercial production systems. On the basis of the present findings, variability in rumen pH is detected among dairy cows with the same dietary and management conditions, and sometimes, the rumen pH can differ more than that associated with any dietary intervention. Cows with a high risk of low rumen pH are characterized by greater sorting against long particles in their diet; lower body weight, feed intake and milk fat; and longer rumination times. However, the mechanisms of these changes are not strong enough to cover the variation in the rumen pH of animals fed the same diets, and more research is needed to evaluate the mechanisms involved. As the variability in rumen pH can affect the results of other experiments at the level of research infrastructure and production efficiency at the level of commercial farms, a precise evaluation needs to be conducted to determine the key elements both biologically and quantitatively. Such biological and quantitative evaluation opens perspectives for managing this problem at both levels of research infra-structure and commercial farms. Pioneering work has started to address individual variability at the com-mercial level, including grouping strategies, animal selection, and increasing feeding frequency. However, this early evidence is not enough to make comprehensive recommendations, and these concepts need to be studied thoroughly. For research experiments, it is also suggested to measure the rumen pH at the beginning of each experiment to use it as a blocking factor or covariate, but this is also the initial level. In conclusion, individual variability in susceptibility to low rumen pH is a common and determining phenomenon among dairy cows in both experimental and commercial production systems but is not well understood in terms of causes and effects and is rarely known in terms of handling and management.