Most of the bacteria live in an environment that is close to a neutral pH. The acid or alkaline nature of a liquid is measured by pH. A pH of 7 is neutral. The ruminant or beef animal consumes mostly roughages in its lifetime. Bacteria break down this roughage into three main energy compounds, called volatile fatty acids, from which the animal gets its energy. When roughage is the main diet ingredient, the pH of the rumen ranges from 6.5 to 6.8, or just slightly acid. Seldom, then, does an animal fed a high-roughage ration eat less due to acid indigestion.
Grain is composed mostly of starches and sugars.
These starches are broken down very rapidly into glucose, and the glucose is converted to lactic acid. However, with an abrupt change to high grain rations, the bacteria cannot adapt fast enough to handle the lactic acid. This leads to an acid condition, with a pH as low as 4 to 4.5. This acid condition also kills bacteria that were doing the job of digestion. Thus, there is not only too much acid, but also reduced rumen function.