Oh wow. The bulge is the bottom of P3... I would be worried, very very worried.
From Pete Ramey's web site
Telltale "hump" or "footprint" of P3 on the bottom of the foot. The material behind the hump is generally sole. The material in front of the hump; lamellar wedge. If you see this on your horse: I'll put this gently- Panic. It's time for sweeping dietary changes and improved hoof care.
You need to have your mare trimmed frequently and regularly. We have soft ground here, so our horses' feet aren't worn down naturally. I trim my horses every 3-5 weeks. Even on rough rocky or sandy ground, you should have your horses' trimmed at least every 6-8 weeks, to keep their feet properly balanced.
For the best hoof growth, you must start with a good diet. Very low starch, no added sugars, no added "fillers" like corn, wheat, grain sweepings, etc. I feed free choice grass hay, alfalfa pellets, flax, and a vit/min supplement. That's it. No feed or grains. My vit/min supplement has added biotin (10 mg), iodine, zinc, copper, and amino acids, all for optimum hoof health. I get it custom blended from Uckele Equine Nutrition. Horsetech.com has a good one too, called High Point. They will increase or decrease any of the ingredients for you to customize the product (their prices include shipping).
A good article on the importance of diet. New Page 14
If your farrier doesn't see anything wrong with the bottoms of your horse's feet or trimming your horse every 16 weeks, then I would find a new farrier, quickly.