I have four horses with four very distinct "treat hog" personalities. I never feed treats as a reward for work. That's what verbal praise and scratchies behind the ears are for.
98% of the time, I only give treats at night when everyone comes in.
Even at that, it's only two of the four, unless the other two catch me.
One because the other three have to go thru his stall to get to theirs. The other one because he doesn't bite anyone on the butt as they pass his stall. Yes my horses come in their stalls at liberty, they know the drill and do their job 100% of the time.
Where I'm going with that is, here's my equine chiropractor's take on feeding horses treats.
On her last visit she said "you don't feed treats do you?" I replied I didn't except for what I mentioned above.
She replied "I just want to thank you for that. It is such a pleasure to work on an entire group of horses that isn't continually lip-nipping. I can't tell you how frustrating that gets, when I'm trying to get them to relax for an adjustment and they keep nipping, looking for treats".
Horses don't need treats very often - the bulk of the time people only feed treats to make themselves feel better. Mr. WTW would feed treats to the horses until his arms got chewed off at the elbows, if I didn't threaten him within an inch of his life. I finally got him to admit it "makes me feel good"