The wildebeest is a ruminant or "cud-chewing" [G 22 / herbivore]. Like sheep, it can devour grass at an incredible rate. The wildebeest is particularly vulnerable to predators during grazing because of its greatly diminished senses. It grazes with it's muzzle to the ground, eyes lowered and hearing impaired by incessant [L3 201 / chewing]. Additionally, because of their fibrous diet, they must be able to digest large quantities of [G 09 / cellulose] along with more easily digestible vegetation.
Rumination enables the wildebeest to rechew food with the head raised and senses alert. It also allows for maximizing available cellulose and digestion of protein rich bacteria as an amino acid source.
The process of rumination in a four chamber stomach works like this:
1. As the wildebeest chews, the vegetation is mixed with alkaline saliva, swallowed and passed to the rumen where it is fermented by bacteria in the gastric fluids. This is referred to as "foregut fermentation."
2. The food is regurgitated in the form of rounded [G 03 / bolus] for chewing. After extensive chew of the bolus or "cud," it is swallowed again and passes to the reticulum -bypassing the rumen.
3. The food mass and bacteria enter the omasum where water is reabsorbed, leaving the mass in near solid form.
4. The mass passes to the abomasum where digestive juices are secreted and the last stages of digestion take place. Nutrients are absorbed in the small intestine. Some fermentation and absorption also occur in the cecum.
This digestive system is highly efficient at maximizing available cellulose, yielding 60% utilization in comparison with the [G 23 / hindgut fermentation] of the zebra in which 45% of the cellulose is utilized.
The disadvantage of rumination is the length of time taken to digest food, limiting the amount that can be eaten and processed in a given period. Food stays in the digestive system of the wildebeest 80 hours, nearly twice as long as in the zebra.
