This 2004 trainee has eaten all the flowers from this musk thistle plant and is moving on to the lower leaves.

My weed-eating cows have been training themselves to eat Musk Thistle since I first taught a cow to eat a weed.  In 2004, my Grant-Kohrs Ranch National Historic Site trainees first learned to eat Canada thistle, leafy spurge and spotted knapweed.  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.  So why would they decide to eat it?  And how much do they eat?Cows choose to eat a new food by generalizing from the familiar to the unfamiliar

Trained cows in all my projects have been adding weeds I didn’t teach them to eat.  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.  I use this theory of generalization when I’m teaching cows.  I start them with what I hope is a somewhat familiar flavor or odor, or I use a familiar feed tub or feeding location.

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 They Eat, They More New Things They Eat

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.  I also noticed that in all the experiments where animals were trying a new food over time, that it took them about 7 days, or 7 tries to reach the maximum they would eat of that new food.  By feeding my trainees 8 different foods, they have 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.

Grazed Musk Thistle - July 2010, Boulder County, Colorado

It Tastes Great! (Thanks to good nutritional value)

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.  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%.  It all depends on the time of year animals are grazing it.

How much will they eat?

My trainees always start with thistles by eating the tops first.  Over the course of a few days, they move on to the larger bottom leaves.  Eventually they begin to graze the entire plant as shown in these pictures of the remains of musk thistle in a the pasture grazed by my experienced weed-eaters in 2010.