Many horses fill their lungs with air during the girth-tightening process. This is their protective response to an uncomfortable situation. In the past, your horse probably has had the girth tightened too fast or too much or simply has been pinched by a poorly fitting girth. There is probably no way to stop the horse from blowing up with air when you tighten the girth, but you can do a lot to make the horse more comfortable during this process, and, through time, it may reduce this behavior. First, check your girth to make sure it is clean and flexible and is not causing rub marks or sores.

Next, always tighten the girth using a slow, 3-step process.

1) Tighten the girth just enough so that the saddle cannot slip backward or under the horse's belly.

2) Walk the horse until it relaxes (and breathes so that it expels that big gulp of air it took), and then tighten the girth enough so that you can mount safely. Usually walking the horse for 1-2 minutes is sufficient. Check the girth for tightness before mounting by inserting two fingers between the girth and the horse at the midpoint of the horse's barrel (belly) between its legs. Checking the girth along the side of the horse's barrel often gives a false indication of a loose girth on slab-sided horses. Insert your fingers from the back toward the front so that the horse's hair under the girth will lay flat when you pull your fingers out. If more than two fingers can be inserted easily, the girth is too loose; less than two fingers and it is too tight. When you mount, make sure you use the horse's mane (left hand holds the mane and reins) and front of the saddle (right hand) to help you mount. Using one hand on the front of the saddle and one on the back will pull even the tightest saddle toward you.

3) After you mount, walk the horse again (3-5 minutes) and check the girth to make sure it is snug. Sometimes the rider's weight compresses the saddle and pad, loosening the girth after mounting.
Following these steps should make the horse more comfortable, and you safer. Over time, once the horse learns that the girth-tightening process is slow and not uncomfortable, it may quit blowing up with air. However, even if your horse does not lose this habit, this 3-step process should ensure that your girth is humanely tightened and is tight enough for safety. Some people advocate bumping the horse in the belly with their knee while tightening the girth to make the horse expel the air in its lungs. This is a bad practice because it reinforces the idea to the horse that the girth-tightening process is painful, resulting in a horse that is highly resentful of the girth-tightening process.