The Web of Life (33-6-3) Ruminating


Ruminants, such as cows, house a vast fermentation chamber in the foregut: the rumen. Horses, elephants, and rabbits divert the roughage into the hindgut (cecum) for the same purpose.

A variety of microbes dine in a rumen, which is the 1st chamber in the 4-chamber complex stomach of cud-chewing herbivores. The animals themselves produce no enzymes to break down the cellulose in the grasses that are the mainstay of their diet.

But the microbial population does. Roughage is broken down in stages, during which the animal regurgitates and chews partially digested food (cud), periodically burping methane produced by the hard-working microbes within.

Rumen microbes feed their host via fermentation. After initially hydrolyzing cellulose to glucose, they ferment the glucose into organic acids that serve as their host’s primary nutrient.


A major portion of animal stool comprises the last meal that microbes shared with their host. While handling the host meal satisfyingly consumed the lives of many gut flora, others are headed out on a group vacation.