The term indigestion describes a disruption of normal reticulorumen function. By this definition, indigestion is a group of problems that involve abnormal forestomach motility or abnormal fermentative activity, which in turn lead to abnormal reticulorumen contents. The various aberrations in motility and fermentation define the type of indigestion such as rumen acidosis, vagal indigestion, and frothy bloat. The subjects of this section are probably the most common types of indigestion but are also the least dramatic and least clearly definable.
Simple indigestion is a disease with acute onset. It is associated with an abrupt dietary change that results in a self-limiting but rapid decline in rumen fermentation. If the dietary or rumen fluid change cannot be assigned to one of the more well-characterized indigestions such as acidosis, alkalosis, or rumen putrefaction, it may be characterized as simple indigestion. It can occur in an individual animal or in several members of a group.
Secondary indigestion is a disruption of normal reticulorumen function as the sequela of other diseases such as endotoxemic infection, abomasal disease, and metabolic disease. It is similar to simple indigestion but typically more chronic in onset because it follows the establishment of another disease entity. The main importance of this condition is that it can confound accurate identification of the primary disease, and it can delay returning to normal health as the primary disease resolves.
Source: https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/indigestion
