Generally horses are back to eating after a few days or a week, the not eating well doesn’t last long.
The not eating well may repeat here and there, but they go back to eating ok.
An apple/cinnamon fig newton in little pieces worked fine for my horse and doesn’t add hardly any sugars to a 1000# horse.
I used to break off a few marble sized pieces, give one, then the one hiding the pill and another or two as chasers.
That used up 1/2 of a fig newton.
If you only give one treat with the pill, they may catch onto it, hide the pill in one, give several treats as chasers.
When I had surgery I boarded my horse for a couple weeks and they were supposed to follow my exact instructions.
I don’t think they did, because he came back not eating his treats.
So now I use other for treats, drill a hole in one and put the pill in it and close the hole with a little senior feed and has worked fine for years now.
Most anything your horse likes for treats will work, if you do the multiple treats tricks consistently.
What really helped our Cushings horse is adding a thyroid supplement.
He finally could lose weight and stay down without needing to almost starve him into staying thin.
Ask your vet about testing for that and adding that supplement, is a powder, if it may help your horse.
Please all of you, even if you never use treats, if you have pushy treat monsters, still consider teaching a horse to take treats, so if you ever have to use some to give pills, your horse will know to eat treats.
Even figuring a way to put a few treats in a feed bucket if you won’t hand feed them, teach a horse those are very good stuff, don’t wait until you have to feed them medications thru them.
If you have to, teach first to eat treats without the medication, then add it later, once the horse is looking forward to them.