Has this always been a problem or is this all of a sudden?
You should get their teeth checked and then try to give it damp with water, some horses don't like dust. Or mayve your horse doesn't like the plants in the hay, you could try with another hay. If she still refuses it, you should ask your vet :)
Get their teeth check for sure but also Alfalfa pellets may look good to them just because it makes the sound grain does. I do it for my mare in the winter when she's not really wanting to eat hay.
Have teeth checked for sure.
You could try sprinkling a little bit of salt on it. Also check his teeth if they have sharp edges he may not want to eat.
try putting sweet feed or molastis on the hay... sorry for spelling