Some thistle varieties, such as yellow star thistle (pictured), are known to be toxic to horses. | Photo: iStock

Q: I suspect at least one of my horses is eating thistle. They’re not eating the big mature plant, but rather the immature rosette stage of the plant. Will this harm them (especially due to the prickly parts of the leaves)? I have been trying to eliminate thistle from the pasture and am making headway. However, I’m unable to eliminate the plants. My pastures aren’t ideal due to the drought over the past few years, but I only let my horses graze a couple of hours a day. —Susan, Austin, Texas

A: It’s challenging to answer this question specifically, because I don’t know the exact variety of thistle in your pasture. Different varieties can have different effects. So, here’s some information that I hope will help you.

With regard to the prickly parts of the leaves, check your horses periodically to make sure nothing has gotten lodged in the soft tissues inside the mouth. If you notice any abscesses, soreness, or pus, contact your veterinarian right away