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United States Department of Agriculture

Agricultural Research Service

A really ugly fish makes a tasty treat

Digesting Grass Is a Gas for Cattle
But does it have to be that way?


Have you ever worked on a group project where one member refused to contribute? When people try to take advantage of a situation without pulling their own weight, we call them freeloaders. Nobody likes them, especially when they're wasting other people's money.

Freeloaders exist in the animal kingdom, too, and even tiny ones can cause major headaches. That’s why ARS microbiologist Michael Flythe is researching a group of microscopic freeloaders that are racking up costs for cattle producers.

The culprits are naturally occurring bacteria that live in the first of a ruminant’s four stomach chambers, known as the rumen. Ruminants are grazing animals, like cows, whose stomachs are divided into four chambers. Unlike human stomachs, rumens contain bacteria that help these animals digest grass and other plant matter.

Bacteria within the rumen function just like students in a study group, Flythe says: “Some members work hard and get the job done, and others just use up resources and don’t contribute anything.”

So who are the slackers in this digestive dilemma? A group of bacteria known collectively as “hyperammonia-producing bacteria,” or HABs.

When cows and other ruminants eat, they actually chew their food at least twice. The first time, they swallow and it goes into the rumen, where bacteria break it down into "cud." Then they chew it again, and the other chambers finish digesting it. All that chewing breaks the food into smaller bits, giving the bacteria more spots to attach themselves, and making it easier for the food to pass through the rest of the digestive system. You can learn more about how the rumen works here: http://www.ars.usda.gov/is/kids/animals/story8/1a.rumen.htm.

While other rumen bacteria are efficiently turning plant matter into cud, HABs break down amino acids, producing a compound called ammonia.  But that's a problem, because ruminants need amino acids to build muscle tissue. To make up for the lost amino acids, producers have to add high protein supplements to their feed, which is expensive.

The animals get a little nutrition from the ammonia, but most of it escapes their bodies in smelly gases or urine, which leads to water pollution--and that's another problem altogether. In terms of usefulness, ammonia production is sort of like playing a video game at your desk during a test: It wastes time and energy, without getting the important task done.

Flythe recently demonstrated that hops can reduce HAB populations. Hops are bitter plants that are natural preservatives. They grow on tall trellises that look like telephone poles.

Flythe didn't feed the hops to the cows, but he did the next best thing. He and his colleagues gathered bacteria from a live cow's rumen and put them in sealed tubes. (There's no oxygen in a cow's gastrointestinal tract, so the scientists put them in oxygen-free tubes to make them feel at home.) In others tubes, they put HAB with no other bacteria. When scientists grow organisms like this in a dish, we call them "cultures."

Flythe grew a few cultures of stomach bacteria and HAB, then he added dried hops flowers and hops extracts to them. Both the flowers and the extracts prevented HAB from growing and producing ammonia. They didn't completely stop it from happening, but they definitely reduced it.

Would the same thing happen if you fed hops to live cattle? It's possible, but it hasn't been tested yet. That's one thing that scientists still need to find out. If so, it could lower costs for producers and decrease gassiness for cows--and that would make feeding time more pleasant for everybody.

--By Laura McGinnis, Agricultural Research Service Information Staff

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Last Modified: 2/14/2011
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