SARA is a disorder of ruminal fermentation that is characterized by extended periods of depressed ruminal pH below 5.5-5.6. Ruminal fluid pH is a measure of the acidity or alkalinity of ruminal contents. A lower pH means higher acidity. For optimum ruminal fermentation and fibre digestion, ruminal pH should lie between 6.0 and 6.4, although, even in healthy cows, ruminal pH will fluctuate below this level for short periods during the day. This drop in ruminal pH is a result of the breakdown of dietary carbohydrates (e.g. starch), particularly from cereal grains such as corn and barley. Grains are high in readily fermentable carbohydrates that are rapidly broken down by ruminal bacteria, leading to the production of volatile fatty acids (VFA) and lactic acid. Under normal feeding conditions, VFA are readily absorbed by papillae (small finger-like projections) on the rumen wall. Once absorbed, VFA enter the cow's bloodstream and can be used for milk production. A graph of rumen pH is shown in Figure 1, from an experiment that fed limited amounts of grain to simulate SARA. Figure 1 also demonstrates the duration of time required for the rumen to recover from an episode of SARA (note the number of hours necessary to return to pH 6.0 after the second grain feeding).