There are two things to consider when faced with a horse eating grass while you're on his back. One is when is the grazing taking place? The other is what to do if you want the horse to stop.
When your horse is surrounded by delicious grass, of course he's going to want to eat it, but then he gets punished for it. That's like taking a child into a candy store and expecting him to have enough self-control to ignore all that candy. That's a heck of a lot to ask!
The natural solution for a horse eating grass is to be understanding and considerate of him, which might mean allowing some grazing time before asking for his full attention. By allowing this now and then?but only when you invite it?you're being a considerate partner and a firm leader. But be sure to give your horse permission rather than just letting him plunge his head down whenever he feels like it.
If you never let your horse eat grass while you're riding, he'll take every opportunity to lunge at the grass, even unseating a rider to get at it. But if you?ve proved to your horse that you're not an unreasonable person, and that you're considerate of his desires, he is less likely to resent you or resist your attempts to shift his behavior.
How To Stop A Horse Eating Grass
First, you must clearly establish your alpha position. When your horse lowers his head, allow him to start munching without even touching the reins or rope. Then smooch and lightly begin tapping his hindquarters, becoming firmer and firmer until his head pops up. Stop tapping right away and rub.
At first it may be a surprised reaction and his head may go right down again. Just repeat the smooch and progressively firmer tapping until his head comes up, then rub him again. Very quickly, a quiet smooch is all it will take to ask your horse to lift his head from eating grass. He will learn to graze when you invite him to, and to stand respectfully until you do. He?ll stop to think whether he's been invited to eat before just hauling you off for a snack.
Patience and Persistence
Be prepared to out-persist your horse on this. Once your phased firmness and timing of the rub is effective, the change is lasting, and it sure beats the old habit of pulling on the reins or the lead rope to stop a horse eating grass?not to mention the resentment that builds in response to your lack of regard for his desires.
If you start getting mad or impatient, remember that it's nothing personal. He's been munching grass much longer than you've been asking him to stop.