Horse not eating hay

[Rough and tumble]

Mine is currently gone off his hay will nibble but is turning away , there was a few horses on the yard that also wasn’t eating the hay , tried a bale externally off the yard and still not fussed , only
Just had teeth done were all ok , very well in himself otherwise , grazing
Happily all day eating hard feed fine wanting treats ect is just the hay

 

[SpeedyPony]

Can you try him on haylage? Was the other bale you tried sweet? Sometimes even if the hay isn't mouldy it can be stalky/coarse and not very appetising (although then they'll usually still pick at it if they're hungry).
Good hay should smell sweet but not too sweet, if it smells like tobacco that can be a sign it got too hot when it was made and the horses (or mine at least) are usually less keen if it's like that.

 

[MidChristmasCrisis]

If he s turning his nose up in the few days immediately after having teeth done it could be that he s adjusting to new biting/chewing surfaces or the hay might smell odd…has a dog peed on it that sort of thing.