Subacute ruminal acidosis (SARA) accounts for a loss of $400 per cow per lactation across the United States. Often, SARA is defined as a decrease in ruminal pH below 5.5 for multiple hours per day. There are no physical signs of SARA, but typically is associated with decreased dry matter intake (DMI) and a correlated decrease in milk production. Oba, et al. (2014) measured DMI, milk production, milk components, and feed sorting behavior of SARA-tolerant or susceptible cows. Milk yield and DMI were not statistically different between tolerant and susceptible groups; however, the tolerant cows had higher milk urea nitrogen concentrations and sorted feed less. The shift in milk urea N suggests the susceptible animals may have impaired fermentation. To better understand the mechanisms behind SARA, it is beneficial to understand how the rumen environment changes during low pH. Markantonato, et al. (2008) conducted an experiment that compared VFA production and absorption rates on a ration designed to simulate SARA conditions (high concentrate) and a ration high in forage. The authors were able to determine there is a slower turnover of VFA during SARA conditions compared with high forage rations. The SARA-type ration also had a larger amount of acetate present in the rumen. A potential explanation for why VFA accumulate in the rumen during SARA conditions is provided by Laarman, et al. (2016). The study by Laarman, et al. (2016) monitored rumen epithelial transporters during SARA or restricted feeding using Ussing chambers. Total, protein-mediated, and passive diffusion VFA fluxes and the abundance of specific rumen epithelial transporters were measured. The transporters, NHE1 and NHE3 were both positively correlated with protein-mediated flux, and only NHE3 was correlated with total acetate flux. These data suggest that shifts in the rumen epithelium may contribute to the sequestration of VFA that occurs during SARA. All of these studies help characterize animal responses to SARA and help us better understand the underlying biology that drives the economic losses associated with this condition.