Overgrazing is not to do with the number of horses on a pasture but rather the length of time a pasture is given to recover from being grazed. | Photo: Thinkstock

Q. As we come into spring and my pastures start to grow, I want to make sure they don’t become overgrazed. I’ve been told they become overgrazed when too many horses graze on them, but what does overgrazed actually mean, and how do I avoid it?

A. Overgrazing is definitely something you want to avoid if you want to keep your pastures healthy. Overgrazed plants will ultimately die, leaving reduced amounts of available nutrition for your horses. While people often believe overgrazing results from having too many horses on a given pasture, the truth is you can overgraze a pasture with one horse. Overgrazing is not to do with the number of horses on a pasture but rather the length of time a pasture is given to recover from being grazed. You can have a lot of horses in a small pasture, and as long as they don’t remain for very long and are removed quickly enough so the grasses can recover, you can avoid overgrazing.

When grasses are grazed, leaf and stem material gets removed, and the plant uses energy stored in the roots to regrow the grazed leaf material. This regrowth is lush, very palatable, and attractive to grazing animals. When properly managed, the horses are removed from the pasture before this lush regrowth occurs, allowing the plant to generate more leaf material that will photosynthesize and regenerate its root energy stores. If, however, the horses remain or are placed back on the pasture too quickly, the root stores won’t fully replenished. Over time, the plants’ energy stores dwindle until they’re no longer adequate to sustain the plant, leading to its death