I’ve seen horses get way more traz than that. And one who was getting dosed 3x/day.
I’ve also rehabbed a fair number of horses from various injuries and I hate ace. It’s not a reliable sedation. You’ll think they’re ok and then they blow through it in seconds. If your vet will dispense Zylazine to you, that’s much more reliable and doesn’t make them wobbly like some of the other sedatives. You can give some in the vein and some in the muscle at the same time and, by the time the IV dose wears off, the IM dose is kicking in. If your vet won’t dispense Zylazine, you could try the IM/IV dose with ace. It might work a little better. No matter which sedative you use or how you give it, make sure you are waiting the appropriate amount of time for it to kick in before you do any moving around. Like, give it and leave your horse in the stall for 20 minutes after if you are only giving it IM.
Also, what blankets you are putting on can really make a difference to some horses. One mare I rehabbed only kept it together if she was blanketed similarly to the clipped horses, despite being unclipped. Not enough to make her sweat, but enough to keep her from feeling any type of chill.
As lots of other people have said, please, do listen to your vet about footing. It can be very important.