Some times dogs have an issue with swallowing their food if not chewed right. That will affect there breathing and gagging. If you have not tried this give them a shot. Elevate their food bowl. Some dogs eat in one spot so that could let gravity help when their head is raised. Get a smaller sized food. We had a Rotty that had a problem. If they don't chew very much then get smaller food and it will be easier to swallow. If they start to gag massage his neck to help push the food down his throat. You might need to give him smaller portions if he likes to eat to fast.
Make sure that it doesn't eat anymore grass and keep an eye on it. Keeping it in a non- grassy area is best. If things get worse talk with a vet.