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Coaxing cows to eat weeds

It was a photograph of a cow eating a dead rabbit that inspired land management specialist Kathy Voth to consider new possibilities for controlling invasive weeds.

Voth, who started out her career in “land management” 11 years ago using brush-eating goats as a fire-prevention tool, turned her attention to cows in 2004.

During the Manitoba Grazing School held in Brandon on Nov. 25 and 26, she brought her radical expertise to the students in her workshop, “Manipulating Livestock for Landscapes,” and challenged them to reconsider long-held images.

“My inspiration was a picture of a steer I saw, with a rabbit in its mouth. It was on phosphorus-deficient soil, and the whole herd was eating dead rabbits,” said Voth, who is based in Loveland, Colorado. “Palatability is not just about taste. These cows were getting nutrients that they needed. Animals choose what to eat based on nutritional feedback, and there are nerves in the rumen that give an animal this feedback from the gut system about what to eat. The more nutritious a weed is, the more likely the animal is to eat it.”

Voth said that, using her methods, livestock producers could train their cows to eat weeds in 10 days – even toxic ones.

“I can teach a cow to eat the weeds in as little as five days,” said Voth. “Animal behaviour is what makes this possible. Positive feedback encourages behaviour. These days I would rather use cows for brush clearing than goats – you need less fencing for cows. This summer I trained 110 pairs in one week.”

The trick is to spend several hours pulling “target” weeds, and gradually introduce them into the cows’ diet over a period of 10 days. Weeds can be as nutritious as alfalfa, said Voth, especially in early stages of growth, and the first step is to “know your weed.” Only a few were actually powerful enough to kill an animal.

“All plants contain toxins,” said Voth. “I look at what kind of toxins there are. Animals will avoid food that makes them sick. But animals will tend not to overeat toxic plants, given a broad choice. A solid stand of your target weed is not a good choice. Your animals must be healthy, not starving, because they need more nutrients to process toxins. Skinny cows defeat the purpose.”

Yearling heifers

To start off the weed-eating education, Voth uses a “training pen,” and recommends using young animals, preferably yearling heifers, who will pass on their knowledge to their offspring. On Day 1 she feeds the cows some rolled corn in a supplement tub, in both the morning and afternoon. On Day 2 she feeds a small amount of barley, with a little molasses sprayed on it, in the morning, and in the afternoon she gives them soybean flakes. Day 3 is some red bran and molasses, with alfalfa pellets in the afternoon.

“I want to get the animals over their fear of new things,” she said. “I feed them things they have never seen before. I just show up, and I dump stuff in feeders each morning and afternoon. We are most optimistic if we have positive experiences, and I just make the cows believe that every time I show up, something good will happen.”

By Day 4, it’s time to slip in the weed angle. Voth serves up hay cubes in the a. m., and in the afternoon it would be a mix of target weeds with red bran. And it’s not necessary to pull huge amounts of weeds – a few handfuls in the bottom of the tub with the bran will do, and because the cows are now used to enjoying their repeated feedings, they readily explore the new “food”. Some weeds require the human to use strong gloves in order to harvest them, such as thistles, but cows seem to be able to eat them without harm, even scorpion weed, she said.

By Day 5, it’s just weeds, and this continues until Day 10 in both morning and evening, until the introduced food item is no longer a new experience. Knapweed worked well in Voth’s trials, along with thistles, toadflax, black mustard, and even leafy spurge. A little watered-down molasses sprayed onto new weeds makes them more palatable, but Voth recommends not relying on molasses too much, and/or thinking it is a “silver bullet.” They won’t always cleanup the tub to start with, but eventually all the weeds will be eaten, she said.

“Once a cow sticks her head in the tub, they all do,” said Voth. “After four days of new foods twice a day, they are ready to try weeds. Behaviour is key. And you have friendly cows afterwards. All you have to do is call them in. A nice temperament is good to start with, but I have trained wild cows just as easily.”

Then it’s time to begin grazing the animals in small pastures, with a mix of both weeds and grass so the cows don’t just eat the best, and leave the rest. A little paddock pressure helps them start in on the weeds, and although they won’t completely obliterate a weed problem, they can make “good inroads,” she said. Sometimes it takes a little time to learn how to eat them as well.

Weeds as forage

“They might not be able to eradicate a weed, but it depends on your goals, because now you have turned weeds into forage,” said Voth. “Not all the weeds might be eaten down, but they can make good progress. And it’s really common for cows who already eat one kind of weed to eat another one. Spotted knapweed is the easiest one to teach.”

Weed seeds can be spread through manure, and Voth advised that grazing before seed formation had occurred could prevent this. Keeping the cattle in just the one area could also contain the weeds. “But they could also be viewed as new forage for you,” she said.

Voth said that we are “on the edge” of learning more about weeds, and that she wanted to find better ways to work in tandem with both cattle and weeds. With some $5 billion spent on herbicides in 2000 in the U. S., which don’t always succeed in eradicating weeds, she wanted to change farmers’ views, and to enjoy her time as a cattle rancher.

“I don’t want to work as hard as my grandpa did,” said Voth, who also hires herself out to train cattle for producers. “I want to sit on a deck and watch my cows, and drink a beer.”

For more information, go to, or contact Kathy Voth via e-mail at: [email protected], or telephone (970) 663-6569. For videos, go to YouTube at:

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