Paul Larson: Let's debunk the myth of the cow's multiple stomach – The Courier Life News

How many stomachs does a cow have?

The trivia games all say there are four. The correct answer is, however, that a cow has one true stomach, the abomasum.

Paul Larson


A cow has three additional out-pockets of the esophagus — the rumen, reticulum and omasum. These three out-pockets of the esophagus are also termed “forestomachs.” Examine the walls of these structures under a microscope, and their esophageal cell origin is evident.

The gastrointestinal tract of a calf changes dramatically from a suckling newborn to a grain- and forage-consuming adolescent. In a newborn calf, the forestomach is very small, but it develops as the calf’s diet transitions from milk to grain and then forage.

Newborn calves, for the first several weeks of life, have a unique adaptation in the forestomachs called the esophageal groove. When a calf nurses milk, consequent neural stimulation signals muscles in the rumen and reticulum to contract and form a groove, a mini-canal, which funnels the milk directly to the true stomach, or abomasum. In essence, this temporary adaptation, makes a calf a monogastric animal like us, for the first few weeks of its life, allowing it to maximize the digestion of its all-milk diet.

If calves are allowed to drink too fast, milk escapes the esophageal groove and accumulates in the small rumen of the young calf. Unlike in the abomasum, where digestion begins after the milk proteins clot in the acid environment, milk that escapes to the rumen tends to ferment and produce volatile fatty acids. Too many of these and the calf can develop a sour stomach, with some shifts in normal gut bacterial populations.

There are several things we can do to prevent digestive problems in our young calves. First, if we slow down the flow of milk through the esophageal groove, we reduce the amount of milk that escapes into the rumen.

We accomplish this by feeding our pasteurized milk with special nipples on the milk bottles. It takes quite a bit longer for a calf to nurse the same volume of milk from these nipples than other rubber nipples or to drink it from a pail. We need to be diligent to replace worn out nipples, which allow calves to suckle too fast.

We need to follow an effective routine of feeding calves. This whole process stimulates the calves to be ready for their bottles of milk, and thereby stimulates proper closure of the esophageal groove. Following the same routine and schedule maximizes the milk that goes directly into the abomasum. Correct milk delivery temperature is important to the calf as well.

As calves begin to eat starter grain, the bacterial and protozoal populations of the rumen begin to change. The grapefruit-size rumen at birth responds to the volatile fatty acids, or VFAs, produced by the microflora which digest the grain, and it begins to grow both in size and in capacity to contract (to mix content); the rumen lining develops papilla for increased absorptive area.

Such rumen (and reticulo and omasal) development begins before a calf is weaned. It needs to be well in progress at weaning to support the calf’s digestion of grain and hay when no more milk is being fed.

Nature knows how best to deliver the milk directly to the abomasum in young calves, by way of the esophageal groove. As a calf begins to consume some grain, pieces of corn and soybean “drop” into the rumen. At first, they aren’t digested much there, and they pass along the GI tract rather undigested.

Soon enough, however, nature works it magic and the rumen develops, growing into a forestomach that occupies about half of a cow’s abdomen and allows her to make meat and milk from grasses and grains.

A mature bovine rumen will hold 50 to 60 gallons of forage, grain and water, and its microflora will digest feed to make VFAs and amino acids that, for the most part, pass along to the small intestines for absorption to the blood stream and delivery to muscles, brain, udder and other tissues.

How many stomachs does a cow have? One.

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