Originally Posted by Tayz
My riding instructor told us that horses get colic if they eat grass and then are ridden and I was wondering if it's true. Anyone have any idea?
No, that is incorrect.
Competitive trail and endurance horses eat grass, leaves, and hay 'during' competition. Food must remain in the gut, along with water, for health to be maintained.
Horses can choke though while trying to eat a mouth full of grass with a bit still in their mouth.
Allowing horses to graze while in tack is generally a training no-no, as many people allow the behavior to get out of hand such that they can't even go on a trail ride w/o the horse reaching for a tree or putting its head down. So, on that basis alone, don't do it.
If you've got enough time to stand around and let your horse munch on grass, then you've got enough time to dismount and take the bridle off and graze the horse properly, or take it back to the trailer and let it munch on some hay between classes or whatever.