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Why Cows That Learn to Eat One Weed Will Choose to Eat Others

Dr. Fred Provenza and some of his non-human colleagues sit down to a meal together.

In 2004, I trained cows at Grant-Kohrs Ranch National Historic Site to eat Canada thistle, leafy spurge and spotted knapweed. Then, they started eating musk thistle as soon as I put them in pasture. When I trained 110 pairs to eat Canada thistle at the Jumping Horse Ranch near Ennis, Montana, they added musk thistle to their diet too. This pattern of learning to eat one thing and trying another continued when I taught cows in California to eat Italian thistle. In no time at all, they were eating bull thistle too. The cows I worked with in Colorado learned to eat two weeds – diffuse knapweed and dalmatian toadflax. But they didn’t stop there. With no pressure at all, they went on to eat ragweed, field bindweed, musk thistle, and about 10 other weedy species.

Why would they do this? The answers lie in animal behavior research, especially the research that tells us how animals choose what to eat. I was lucky to be at Utah State University in the late 1990s where some of the most renowned scientists in the field of animal behavior and learning were working. Dr. Fred Provenza, and his colleagues Carl Cheney, Beth Burritt, Juan Villalba, shared their discoveries with me. They inspired me to think, “Well, if all that is true, then I should be able to teach a cow to eat a weed” and their work was the basis for the training steps I developed. And they show why “educated” animals are willing to try other new foods in pasture.

Educated Cows Choose to Eat a New Food by Generalizing From the Familiar to the Unfamiliar

When I was figuring out how to teach cows to try a new weed, one of the research papers I found said that creatures tend to “generalize.” They consider something new, see if it is similar in any way to something they’re familiar with, and then decide what to do with it based on the familiar. Scientists found that rats presented with a new food were more likely to try it if it had a familiar odor or flavor. It works the same for people. If I invite you to my house and say, “We’re having frog legs for dinner!” You might think, “YUCK!” But if I tell you, “They taste just like chicken,” you might decide to give them a try.

Here’s how generalizing works in this situation: Every morning and afternoon for 4 days, I feed a snack of an unfamiliar but very nutritious food. Because trainees get good feedback from the nutrients, they like the new foods, and expect that everything I put in the tubs will be tasty. Then, when I add weeds, that’s just one more strange thing in a series of strange things, so they’re happy to try them,

I use this theory of generalization when I’m teaching cows. I start them with what I hope is somewhat familiar and then use that to introduce other unfamiliar foods. This can work for foods or for feeding locations. For example, when I was teaching heifers in Colorado to eat diffuse knapweed, I knew that they had eaten dried ear corn over the winter. They’d also eaten protein supplement out of big black tubs. So, the first day of training, I lured them to the supplement tubs with a trail of rolled corn and then poured it into the tubs to get them started. I used a familiar flavor and a familiar feed tub. Then, for every feeding after that, I added a new, but unfamiliar feed. They learned that the tubs (and I) meant good food, so whatever went in the tub was a new, tasty treat.

How does this relate to choosing to eat different varieties of thistles in pasture? Well, I don’t know what thistles smell or taste like to cows, but I assume there is something similar about their flavors and tastes. At a minimum there is something similar about they way they look, so that could be one reason they decide to try musk thistles after learning to eat Canada thistle.

The More New Things Trainees Eat, the More New Things They’re Willing to Try

One of the reasons I feed my trainees lots of unfamiliar foods is that research tells us that the more positive experiences a creature has with new things, the more likely they are to try other new things. Of course the converse is true too. The more bad experiences a creature has, the less likely it is to try more new things. That’s why I focus on making sure that my trainees have positive experiences every time they see me and they try a new food.

But how many new things do they need to try to become optimistic? l noticed that in all the experiments where animals were trying a new food over time, it took them about 7 days, or 7 tries to reach the maximum they would eat of that new food. For the training process, I translated that into giving trainees 8 new food tries over 4 days.

By feeding my trainees 8 different foods, I give them lots of positive experience with new things, and they seem to become very optimistic about new foods. Then, when they hit the pasture, they start looking at what’s growing there in new ways.  It’s all potential food to try.

Weeds Taste Great! (Thanks to Good Nutritional Value)

This is the most important concept to understand in the whole training process. No matter how optimistic my trainees are, they aren’t going to do more than try a new food if it doesn’t give them positive feedback. Positive feedback comes from the nutrients in a food. As I explained in last week’s article in this series, the more nutritious a food is, the more likely an animal is to eat it. The lower in nutrients, the less the animal will eat. Animals get negative feedback from toxins in plants. Toxins reduce the amount an animal will eat, and the higher the dose, the less it will eat. This is why I make sure to give trainees high protein feeds throughout the training process. They get good feedback so they’re willing to keep coming back for more, even if everything I give them is a bit strange.

This calf is eating musk thistle, just like her mom taught her to do.

That’s also why they start trying other foods in pasture. For example, in 2009, I tested musk thistle because I watched my trainees grazing it. I found that the musk thistle flowers were 11.2 % protein, making them much better than the grasses growing at that time. Other resources indicate that thistle protein values can range from 17 to 25%.  Of course, as with all forages, nutritional value changes over the course of the grazing season. But, in general, I’ve found that “weeds” maintain their value much longer than grasses.

Bonus Material

For paid subscribers, I’ve provided a training recipe and a list of weeds that are safe for livestock to eat. Read the articles and then click on the bonus material to download.

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Kathy Voth
Kathy Voth
I am the founder, editor and publisher of On Pasture, now retired. My career spanned 40 years of finding creative solutions to problems, and sharing ideas with people that encouraged them to work together and try new things. From figuring out how to teach livestock to eat weeds, to teaching range management to high schoolers, outdoor ed graduation camping trips with fifty 6th graders at a time, building firebreaks with a 130-goat herd, developing the signs and interpretation for the Storm King Fourteen Memorial trail, receiving the Conservation Service Award for my work building the 150-mile mountain bike trail from Grand Junction, Colorado to Moab, Utah...well, the list is long so I'll stop with, I've had a great time and I'm very grateful.


  1. I trained cows and calves 8 1/2 years ago to eat Ironweed. The next year they were eating multiflora rose and autumn olive. They continue to expand their selection to Japanese Stilt Grass, Thistles, etc. I turned a group of yearling steers into a field that had Joint head grass last year. They had never seen it before and they did a very good job of eating it. Btw, Joint head grass and Japanese stilt grass both have a TDN in the high 60’s. One other interesting thing is the following summer after the initial training, the then yearling heifers (they were calves at time of training) taught a yearling Bull that was not even on the farm the training year to eat Autumn Olive.

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