I won't even use Moxidectin on my horse, but have used ivermectin and fenbendazole on my donks.
When I first rescued them their feet were in horrid condition. My farrier started slowly, but the female still got very sore in the legs, shoulders, and back because of the curvature of her hooves were so bad. I checked with my local vets about an oral pain supplement as well as the doseage for banamine.
They said because of the slower metabolism in donks, once you figure the dosage based on weight, half that again.
(So if a 1000lb horse gets 2oz of medication X (whatever) then a little 250lb donkey initially would seem to get 1/2oz, but... half that again for 1/4 oz.)
Dewormers were ok to give based on regular weight, but other meds sometimes need to be cut down.
Don't know of that helps you to know...