It's possible he was grunting if his stomach was feeling uncomfortable. You'll just want to keep an eye on his poop to make sure it gets back to normal, doesn't stay soft, get really tiny, or stop altogether. Also check the stomach for bloating. Is his behavior and activity level staying normal? He's not sitting hunched up not moving around much, or laying down more than usual, and changing postions frequently, like he's trying to find a position of comfort?
If you can find a feed store near you, they will often have bales of grass hay. You don't have to feed timothy. Any non grain grass hay is fine(bermuda, coastal, meadow, orchard, oat-without seed heads, etc). It's also a lot cheaper to buy a bale, than those little pet store bags. Bales are usually $5-20, and they are mostly around 50 lb, though some may be heavier. You want to make sure it is good horse quality hay, that hasn't ever been wet and gotten moldy, and a good green color on the inside of the bale is a good thing to look for too.
