Weed Whackers

If you're tired of spending time and money to spray the same weeds every year, here's some good news. The solution may be grazing in your pasture. In summer 2004, we successfully trained cattle to eat Canada thistle, leafy spurge and spotted knapweed in a project sponsored by the National Park Service and Grant-Kohrs Ranch National Historic Site in Deer Lodge, MT. The process is based on 20 years

If you're tired of spending time and money to spray the same weeds every year, here's some good news. The solution may be grazing in your pasture.

In summer 2004, we successfully trained cattle to eat Canada thistle, leafy spurge and spotted knapweed in a project sponsored by the National Park Service and Grant-Kohrs Ranch National Historic Site in Deer Lodge, MT. The process is based on 20 years of research by Utah State University's Fred Provenza that shows livestock behavior can be modified to manage vegetation.

My process revolves around understanding how animals learn and how they choose what to eat. The following easy steps can train cows to utilize many other forage species in their diets.

We began in February with a small herd of yearling Hereford, Shorthorn and Longhorn heifers. While in dry lot, the animals were periodically given a wide variety of unfamiliar but nutritious foods to encourage them to try new things.

Each morning — for four days/weed — our team spent an hour picking newly sprouted weeds, mixing them with a familiar flavor and serving them to our project herd. After 4-5 days of experience with each weed, the cows went to pasture and continued to eat the target weeds throughout the summer, mixing them with other grasses and forbs.

This technique may not totally eliminate weeds, but it can improve your bottom line by increasing forage availability and providing a low-cost alternative to herbicides.

Step 1

Know your weeds

Research shows animals choose what to eat based on feedback from nutrients and toxins in those foods. The more nutritious a weed, the more likely the animal will eat it. Many weeds, including Canada thistle, leafy spurge and spotted knapweed, are similar in nutrition to alfalfa.

All plants contain toxins, but weeds generally contain higher levels. At low levels, toxins reduce the amount of that plant an animal will eat. At extremely high levels, plants may be toxic, perhaps even fatal.

Scientists have begun to identify the toxins in plants, as well as supplements that help animals deal with their effects. For example, while Canada thistle's high nitrates can accumulate and cause death, molasses- or corn-based supplements allow ruminants to process them without negative effects. When supplements aren't identified, mixing other forages with the target weed enhances an animal's ability to process toxins.

Step 2

Choose your animals to fit the weed

Younger animals are more likely to try new things but often are more susceptible to some toxins. Females are a good choice because they can pass food selection habits to their young. Males may be a better choice when working with weeds that cause reproductive problems.

You needn't train your whole herd. Research shows experienced animals will teach inexperienced herdmates. Our bull was eating weeds after watching our 20 project heifers for only a few minutes. Make the process easy on yourself and choose a number of animals you can easily manage.

Step 3

Maintain a healthy herd

The key to this process is an animal's nutritional state. A starving animal's ability to handle toxins is reduced. While an animal can be starved into eating something, the result is reduced weight gain, reduced profit and an animal less likely to try other new foods.

We fed our animals half their hay in the morning, weeds at noon and the rest of their hay after they'd cleaned up their weeds. Weeds only made up 10-15% of their diet during training to ensure they had a good experience and maintained good condition. Heifers averaged 3.1 lbs. gain/day before the bull was put in with the herd.

Step 4

Reduce the fear of new things

Just like people, animals may not try new foods, even if they're beneficial. Animals that have good experiences with a wide variety of foods are more likely to try other new foods.

In the pilot project, we spent two weeks in the winter giving our cows new, nutritious foods like alfalfa and beet pulp pellets, rolled grains and molasses-based tub supplements. It's easy when animals are in winter dry lot. Using the same feed bucket or tub every time will help in the next step.

Step 5

Make the unfamiliar seem familiar

For example, you're more likely to try frog legs if I tell you they taste like chicken. Similarly, animals are also more likely to try a new food if it has a familiar flavor.

When weeds sprout in the spring, cut some and put them in feed buckets or tubs and add a familiar flavor. We sprayed on a molasses-based supplement and added corn, oats and barley as our familiar flavors. Letting the molasses dry before serving improved our success.

Don't expect your animals to clean their plates the first day. Research shows they try things a little at a time and eat more after experiencing positive effects from the nutrients. It took 4-5 days for our heifers to become comfortable eating a new weed.

Step 6

Field-test your animals

We began in small pastures to ensure our animals didn't just eat the best and leave the rest. Be sure your animals have plenty of feed to mix with their new weeds and don't expect them to eat solid stands of the target weed. They will always need to mix in other foods if you want them to be successful, healthy weed managers.

We included a molasses supplement in a tub to ensure animals suffered no negative effects from eating thistle. Once on pasture, they began eating weeds, stripping leaves and stems even though it was late in the growing season. We moved the cows when there was 4-5 in. of stubble remaining to allow for grass recovery.

Step 7

Observe and adapt

Adjust your grazing plan by observing what and how your animals eat. Timing is important. Early season may allow for too much regrowth.

For example, some weed species will push out two or more blooms for every one eaten by a cow. Thus, you may need to have your animals return to the pasture or adjust the timing of grazing.

Grazing plants after they've gone to seed risks spreading weed seeds via manure, so animals may need to be quarantined for 5-7 days to allow seeds to pass through their systems. In addition, late-season grazing may not stress the weed enough to reduce its ability to grow the following year.

Other items to remember:

  • First impressions count. If you're not prepared to ensure your animals get a good first impression, you're not ready to start. If an animal's first experience is negative, the animal will always eat less of the target weed, no matter what it learns later.

  • Stress kills. Animals experience stress when moved to an unfamiliar location, when separated from familiar herdmates or when worked by strange people in unexpected ways. Stress also increases plant toxins' effects on the body. You'll be more successful if your animals are in a familiar place with familiar companions when you give them new foods to try.

  • The impact of Voth's 2004 trials on 2005 animal behavior and weed control won't be known until this summer, she says.

“I return to Montana in June to put the project herd into pasture with leafy spurge, to watch as their calves learn what to eat, and to collect information on weed regrowth in last year's pastures,” she says. Look for a future update in BEEF magazine.

Kathy Voth is a consultant, researcher and educator in sustainable land management. Visit her Web site at www.livestockforlandscapes.com.

It's not too late

It's not too late to begin using your cows as weed managers this spring, even if your herd is already in pasture, Kathy Voth says.

“If you've researched your weed and are sure it's not toxic to your animals, begin by bringing a manageable number of young cows back to dry lot for two weeks,” Voth says. “Manageable,” she adds, depends on the amount of time you have available.

She says she's found the time invested in a project herd of 20 head to be minimal, but the impact was noticeable when she put the animals back with the main herd.

“In less than a month, I could see the animals with no training beginning to include new foods in their diets, she says.

Voth recommends producers spend the first 10 days with their cows on Step 4 of the process, introducing them to a variety of nutritious but unfamiliar foods and teach them “good things come in black tubs.” If you know the supplement that will help them eat your target weed, introduce it to them during this time, she says.

Next, spend the last four days on Step 5, introducing the animals to the target weed using a familiar flavor and the same tubs used for Step 4.

“Once your cows are eating the weed well, put them back in with the rest of your herd so they can get to work,” she says.