I have avoided writing about hoof angles, because there is not a simple answer that I can give you. I am going to talk about the angle of the hoof wall at the front of the hoof. The angle of the hoof should be the same as the angle of the shoulder and hip. This usually means the back hoof wall has 2° more angle than the front hoof wall.
Every breed type will have different conformation so the angle to their hooves will be different. You’ll want to visually adjust your horse’s hoof angles, but that can be difficult so I will hazard to give you some ballpark figures. A working quarter horse style will usually be 53° in front and 55° behind, those are the most common horses in my area so that’s what I saw the most. Now remember some quarter horses, like the English style, are for all intents and purposes a thoroughbred with a more sloping shoulder, therefore they typically run 50° in front and 52° behind. The Arabian horse will have a steep shoulder, most Arabians I have seen have pretty steep angles on their hooves when matched to their shoulder and hip, like 55° in front, and 57° in back. Some Arabians even go even steeper.
Now if you happen to be trimming a mule I will tell you what my mule’s hoof angles are, they are 57° in front and 59° in back, that is just the way she is built, actually I could trim her a little bit steeper to match the shoulder angle better, but she is a little over at the knee, I don’t want her to be buckling her knees so I trimmed her with less angle. And that is where you have to use your brain, see where your horse is more comfortable, and remember some horses just do not grow or at least accumulate any heel whatsoever, so you probably will never get the ultimate hoof angle on that particular horse. Genetics play a big role in hoof quality and some horses just don’t have the genetics behind them. Some of the breed associations can be thanked for that, they bred for the head and cheat the feet.
By trimming the hoof down to live sole at the toe, and trimming the heels to the back of the frog, you should be pretty close to the proper angle, on most horses. You can check this with a hoof gauge to see how you’re doing. When trimming your horse make changes in moderation, if you suspect you’ve left the toe too long for a while, don’t change it in one trimming, make the changes over the course of a couple trims.