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What Do Cows Eat, and Why?

By   /  April 10, 2017  /  1 Comment

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This steer was part of a trial to see the effects of grazing on phosphorous deficient soils. The herd decided to solve the problem by eating dead rabbits found in the pasture for the phosphorous in their bones. It’s just one of the many examples of why Fred Provenza decided to do research on how animals choose to eat and where to live.

On its face, this seems like a silly question. Don’t we all know what cows eat?! So when Fred Provenza, as a new professor at Utah State University, chose this question for his research focus, there were some raised eyebrows. Three decades of research later, it turns out that Dr. Provenza’s research was ground-breaking, giving us important insights into how animals choose what to eat and providing the foundation for new ways to work with our livestock as land management tools.

What Fred discovered is that animals have to learn what to eat. They learn from their mothers, their herd mates and from personal experience with nutrients and toxins in foods. That means that animals can add things to their diets beyond what we typically consider appropriate for them. He found that animals use the feedback from nutrients and toxins in forages to mix a diet that is perfect for their individual needs. That’s why, when he compared the weight gain of steers eating a standard Total Mixed Ration (TMR) with weight gain of steers allowed to choose from all the items in the TMR, the animals that could choose gained just as well as the steers on the TMR, but at a 20% less cost. Finally, he found that the way we manage our livestock influences their diets. When we’re convinced that cows only eat grass, we make pastures that are just grass, and we move them when we all the grass is eaten, even if there are other plants there that would be perfectly good forage. By doing this, we’ve created cows that don’t know things besides grass could be grazed.

Fred summarized what he learned in his decades of research in these 8 Behavior Principles.

Behavior Depends On Consequences

Positive consequences increase the likelihood of an animal repeating a behavior and negative consequences decrease the likelihood of an animal repeating a behavior. Positive consequences have fewer negative side effects.

Mother Knows Best

An animal’s mother has the greatest influence on the foods an animal chooses to eat and where it chooses to live. Once trained, animals will pass new behaviors on to their offspring automatically. You can see this in action in this video of a demonstration Fred and his colleagues did using sheep. (That’s my voice narrating the video.)

Early Experiences Matter Most

The behavior of animals changes throughout their lives based on experience. Animals are more likely to try new things, including foods, early in life. Experience can change the an animal’s physiology, neurology, the structure of its body even gene expression.

Animals Must Learn How to Forage

Believe it or not animals actually have to learn how to eat. Young animals acquire foraging skills more quickly early in life than older animals. The goats in this video show you what that means.

Animals Avoid Unfamiliar Foods

Animals don’t like to eat new foods. Eating new foods is risky because they may be toxic. As long as animals have plenty of familiar, nutritious foods to eat, they generally avoid eating new foods.

Palatability Depends on Feedback from Nutrients and Toxins in Food

When an animal eats a food, it is digested releasing nutrients and toxins. These compounds are absorbed and travel to the cells and organs of the body. Signals are then sent back to the brain to tell it how well a food meets the animal’s nutritional needs. The brain then pairs the food’s flavor with it’s benefits, toxicity or lack of benefits to the body.

Nutrients Increase Palatability
Animals learn to eat foods that are nutritious and avoid foods that are low in nutrients. Their bodies tell them which foods are which based on feedback from the gut.

Here’s an example from a demonstration of this that Fred and his colleagues ran:

Toxins Decrease Palatability
Animals learn to avoid foods that are toxic. Their bodies tell them which foods are harmful based on feedback from the gut.

This demonstration gives you an idea of how well this works for animals:

Changes in Food Preferences are Automatic
Think animals can’t be this smart? Changes in palatability occur automatically due to feedback. Animals don’t need to think about or remember feedback from the food. Even when animals are asleep, feedback still changes palatability.

Toxins Set a Limit on Intake
In most cases, animals only eat small quantities of plants that contain toxins because toxins in plants set a limit on intake. Most toxins do not cause death or obvious sign of illness instead they keep animals from overeating any one plant.

Variety is the Spice of Life

Providing animals with a variety of foods on pastures, rangelands and in feedlots allows them to avoid toxins and balance diets to meet their own unique needs for nutrients.

Everybody is an Individual

Individuals within a species vary widely in their ability to tolerate toxins and their need for nutrients.

What Can You Do With This?

There are all kinds of ways you can use this information and probably have already used it. You’ve used it when you put new livestock with old timers to learn where and what to eat. You’ve used it whenever you set up an electric fence knowing that the consequence of touching it would teach the animal to stay inside the pasture.

A rancher raising bison in feedlot used this information to reduce his workload and increase the animals’ average daily gain by setting them up to mix their own diets.

Want to meet Fred and hear about his latest work? He’ll be speaking at this conference.

I used it to figure out a method for teaching cows to eat weeds. Since weeds are as good as alfalfa in nutritional value I knew that cows could eat them if I could just get them to try. I created a routine to get cows over their fear of new things which included giving them tasty treats in tubs. They learned from the good consequences of eating tasty treats to try everything I put in the tubs, so it was easy to get them to taste the weeds.

One of the things I like best about Fred’s research is that it points out importance of asking questions, even when everyone else thinks the answer is obvious. Because he did this research we now have options and opportunities with our livestock that we never would have had otherwise.

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About the author

editor and contributor

Kathy worked with the Bureau of Land Management for 12 years before founding Livestock for Landscapes in 2004. Her twelve years at the agency allowed her to pursue her goal of helping communities find ways to live profitably AND sustainably in their environment. She has been researching and working with livestock as a land management tool for over a decade. When she's not helping farmers, ranchers and land managers on-site, she writes articles, and books, and edits videos to help others turn their livestock into landscape managers.

1 Comment

  1. Hubert McClelland says:

    Great work, I using replacement dairy heifers to graze bedstraw which is an invasive species in forage acres is eastern Canada. If I graze intensively it seems to kept in in check. my problem is that the roadsides and fallow land provides lots of seed to spread.

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