Join Date: Aug 2009
Location: New South Wales, Australia
Most traditional stock saddles are built for narrower horses, as apparently stock horses used to be built more like Thoroughbreds (they're being bred wider now). So it's likely that a stock saddle won't fit a wide horse, unless it's a wide make. The weight can easily make the difference. Also, it might not have fit him too well in the first place, the angle of the front has to match the angle of the horse's back. Just because it "sits" there, doesn't mean it fits. If you have some pictures maybe you can get more advice.
There are lots of saddles out there that will fit a wide horse. You might want to look at something with an interchangeable gullet system, so that when he loses weight you can keep the saddle. As he's just a lease, an adjustable saddle is more likely to fit more horses, if you get a different horse later on. If you're looking for a stock there might be some halfbreed stock saddles that fit him (as they're built wider), however with his breeding you have to make sure they're not too long for his back.
If you're not experienced in saddle fitting the best option is usually to get out a saddle fitter. Many of them will have a collection of saddles to try on your horse, or are affiliated with a saddlery so they can borrow saddles you're interested in and try them on.