Does Kern's original Horchata contain Gluten?

I'd avoid it. Sometimes, they use grain to create the "natural and artificial flavors." It's not worth the risk.

Cow milk does not contain gluten, however if you have been put on a gluten free diet because of celiac disease you might have trouble digesting the milk at first until the small intestine repairs itself. Take lactase before you drink the milk and that will help.