I agree with not changing the feed - as log as he's getting enough hay every day with no long gaps in between feeds and the pellets are good quality - not high starch/sugar based then its best to leave him for now
The loose droppings are a warning sign that something isn't right in his digestive system and combined with the grumpy attitude when girthed might make me give him a little break from riding until its resolved - perhaps some quiet work on the lunge?
Except that he had loose stool since the day we got him, on October 3rd 2015 (literally, I remember because it's the first thing he did when he got on the trailer and the seller just said it was because he was nervous... but it has never gone away). This isn't new. We've been riding him all that time... and he's happy when being ridden. It doesn't mean I'm not going to keep trying to figure out if this is something we can change. It's entirely possible he's been living with this for quite some time. Or it's possible this is just how his stool is... he does drink a lot of water. And yes, I know, it might be a sign of IR or Cushings, but the vet and BO do not not think so. Just in case though, we are avoiding anything with high sugar or high starch in his diet. And if the worming and ulcer treatments don't help, we will do a full bloodwork analysis.
I know some of you think I'm over-thinking this and others think I should be more aggressive with treatment... yet others think I should just deal with it as a behavioral issue. I really do appreciate hearing a diversity of opinions because it helps me consider all possibilities. But believe me when I say I am exploring ALL of those possibilities, consulting with vets, the trimmer, a saddle fitter, an equine massage therapist, a horse trainer, and a horse nutritionist to get to the bottom of something that only bothers Harley about 2% of the time. Because 98% of the time, he looks and behaves like a happy, healthy horse. He is nippy for about 5 minutes after he is girthed, which is about 3-5 times a week. And I can't start changing everything around too quickly because it might aggravate the problem and we might then see a sudden improvement and not know whether it was the wormer, the ulcer meds or the change in diet that did it. I feel it's necessary to work through this by a process of elimination and give each treatment some time to work. Knowing the cause will help me make the lifestyle changes that will prevent it from recurring.
Of course I'd like to see my horse be happy 100% of the time and I do take nippiness very seriously. But it may take some time. I will keep you all posted!
Oh, and yes, he gets hay to munch on all day and part of the evening. It makes up the bulk of his diet.