The gullet of a saddle is the channel that runs down the center of the underside of a saddle, in between the panels. The gullet bridges the horse’s spine so it is an important part of the saddle design. If the gullet is narrow, it can pinch the muscles on either side of the spine which ultimately will make your horse’s back stiff or sore. The horse’s spine is where the nerves of the back are located; to prevent the saddle from impinging on these nerves, the gullet needs to be wide enough to distribute the weight of the rider on the horse’s muscle.
Many people confuse Tree Size with Gullet Width. Tree is a completely different measurement: it refers to the distance between the bottom of the points of the tree. This measurement is either described in centimeters or as medium, medium/wide, etc. Please note that these excellent descriptive photos are from: How to Measure an English Saddle. The rest of the photos are mine, but these just illustrated the concepts more clearly.
I think that part of the confusion between tree size and gullet width is due to the popularity of the Wintec saddles with interchangeable gullets. The concept promotes the idea that by interchanging the “gullets” you can adjust a saddle from a narrow tree size to an extra wide. And you can. But the Wintec gullets are inserted into the front of the saddle and they change the angle of the tree — and may change the front part of the gullet slightly. If you look at the photo on the left, imagine that the inverted “V” is either narrower or wider. In some saddles, the saddle gullet is wider at the pommel end and narrows over the length of the saddle.
In fact, there are saddles where the gullet becomes very narrow indeed. In the photo below are two saddles: an old Hermes close contact saddle and a recent model County cross country saddle (the Extreme). They are both medium trees, according to their manufacturers, but they are different sizes. The Hermes is a 16.5″ and the County is an 18″.
In comparison, the County has a nice wide gullet. In fact, you can comfortably fit three fingers in the gullet. I’ve read that the “three finger” rule is a good starting point for gullet width, although each horse is different.
The implications of this difference comes when you look at the saddle on a horse. The model here is my 17 year old Trakehner gelding, Kronefurst. The first photo shows the Hermes. You can see that the gullet offers barely any clearance over the spine and the panels sit very close to the spine and will not distribute a rider’s weight effectively.
In comparison, look how nicely the County clears Kroni’s spine. The panels sit very nicely on his back and will distribute a rider’s weight very well. And they should! I have my saddles checked and fitted by a professional saddle fitter at least once a year.
Given that narrow gullets can impinge on a horse’s spine, why do manufacturer’s make them this way? One rational for making the gullet narrow is for rider comfort. Many people like riding in a saddle with a narrow “twist”, and some saddle manufacturers simply bring the panels closer together toward the back of the saddle to accomplish this. However, it’s not nearly so comfortable for your horse!
Can a gullet be too wide? Yes, if it reduces the size of the panels to the point where they can no longer adequately distribute the rider’s weight. This is a fairly unusual; it is more typical for gullets to be too narrow.