This document discusses evaluating dairy cow manure as a way to understand rumen function and digestion. Manure evaluation can indicate whether changes need to be made to the cow's diet formulation. Fermentation in the rumen and hindgut produces organic acids, microbial protein, and gases. Insufficient fiber intake can lead to acidosis and poor digestion seen in manure. Proper particle size and effective fiber are important for rumination, buffering, and manure characteristics. Certain feed ingredients or moldy feeds may cause diarrhea visible in manure.