5 July 2016

Equine Anatomy Part 2

Equine Anatomy Part 2

A diagram of muscles- note the Longissimus and the Spinalis muscles- very close to the saddle fit area.

What is a Wither and where can I find it on my horse?

A wither is the bony ‘bump’ if you like, at the base of your horse’s neck, above and in between the shoulder blades.

When you run your hand over it, it feels rather bony and lumpy, but it is also made up of many muscles, three of which being the Longissimus Dorsi, the Spinalis Dorsi and the Trapezius muscle (see diagrams above). We measure a horse’s height from this point- this is a high as we will be riding and it is the place we measure when looking for a horse to suit us. The pommel of your saddle sits here and it is an extension of the horse’s shoulder bones. One significant bone which rises up through the shoulder to just under the Wither is the Scapula- a large triangular-shaped, flat piece of bone, which is slightly concave on the inside to allow for other bones and organs, with cartilage at the top which helps the horse to move. You will be able to see this part move as the horse does. The Scapula is a key focal point for the horse’s movement, as we will find out in the coming weeks, but it is a significant part of the saddle fit process and should be considered when looking for a correctly fitting saddle.

A diagram of the horse's muscles- mainly highlighting how large the Trapezius Muscle is.

You can see the large bone in the shoulder called the Scapula- a major bone with soft cartilage at the end that must be protected when fitting a saddle.

How does the Wither change over time?

The Wither is an important point of consideration for any saddle fitter.

First of all, you need to know that withers come in all shapes and sizes. You can expect each breed of horse to have a different shaped wither to the next and not only that, but no two withers in the same breed will be the same!! So do not worry if you have two thoroughbreds, for example and both their withers are different. This is just a natural process and each horse’s individual growth and exercise regimen from birth will determine the shape of your horse’s Wither today.

The age of your horse will also determine the shape of the Wither. As your horse grows, so will the back and Wither of your horse, so expect to see many changes over the years if you own your horse from birth.

Withers of a foal — flatter and immature with very little definition.

As a foal, your horse will have very immature muscles. The Trapezius muscle, the Longissiums Dorsi and the Spinalis Dorsi have very little tone or shape to them at this stage. These muscles are the saddle bearing muscles that are relevant to saddle fit later once the horse is broken in and ridden away. In fact, as the horse is so small, the back and withers are very narrow and at this point, cannot carry any weight on its back. This is the same for all breeds; however ponies or even donkeys that do not reach a greater height still develop stronger muscles just the same at an older age.

As your horse grows and develops into a two or three year old, the muscles begin to develop and change in the shape of the Wither “can develop rapidly too”, (K. and K. Baker, The Horse.com). As your horse grows, his back widens and his Wither grows too. A two year old horse’s muscles are still immature at this stage, but will have grown in tone and shape since the foal or weanling stage. You may also be able to see a difference between the withers on a colt or filly. With testosterone, the colt’s withers may also be slightly larger, whereas a filly may exude finer features, particularly in breeds such as the thoroughbred or standard bred.

A two year old. Starting to mature- more definition in the Wither.

As we see the horse grow into a three or four year old, the withers grow again, gaining more tone- which means they start to thicken due to the load or force exerted through growth and speed of the horse. The same is also true when the horse is broken and begins to carry weight. A horse initially broken in may feel ’soft’ in the back. However, once the horse is ridden more often, his Spinalis Dorsi and Trapezius muscles (and to a lesser extent the Longissimus) will thicken and toughen and strengthen. We know this from the different disciplines your horse does. The more often the horse is ridden, the stronger and fitter it becomes. If a horse is turned out, the muscles become flaccid and soft. Humans show the same tendencies- over Christmas we might put a few cheeky pounds on due to being on holiday and eating too many sweeties, but when we return to the gym or exercise, our muscles will feel sore and weak to begin with, but they strengthen quickly.

Once your horse is broken, no matter what age they are, the saddle fitting process becomes so important to review as your horse will change shape countless times through the wither and saddle-bearing areas. As he grows older, your horse will have a wider back, with more developed muscles along the withers and down through the shoulder. Think of it like a human- as you grow, exercise and develop, your muscles grow in capability too. Your muscles will never be weak or immature again, but they may change in ability if, for example, you do not exercise for a period of time.

The withers are the same and now that your horse is broken and wearing a saddle, he will need to be re-fit to change with his exercise. His muscles have developed from weak, immature muscles to adult, strong toned muscles. Depending what discipline your horse does, he will have stronger or weaker muscles too;

“Horses that are put into serious competition or work might start out heavier and wider while they are out of condition, but by mid-season they will have lost some fat in the top-line and added muscle in the shoulder area”. If your horse was to compete for a long period of time, they would probably become thinner and narrower on the top due to their workload. (K. and K. Baker). So, horses change shape along their back and wither with the amount of work they do. With different breeds, the change will be different in the degree of narrowing or widening, but every horse with work will grow stronger, narrower withers and a leaner back whereas unused horses will grow wider, softer withers.

Peter demonstrating the shape and size of the Scapula in a young thoroughbred and how and where an old half tree saddle sits on the horse's back. Follow us for more on how trees affect your horse next week.

So how does this shape affect the saddle fitting process?

So the shape of the Wither changes in each horse. A horse that is younger has lesser developed muscles than an older horse in work. This also changes if the horse is in or out of work. Depending on the amount of fodder your horse is getting, whether it be grass or hard feed, the horse changes shape or gains or may lose weight. A horse at pasture will be more ‘out of shape’ than a horse in work kept in a stable. So it is important that you have a saddle that will fit your horse correctly- even when they are young and just broken. If the saddle fits incorrectly, it could create irreparable damage to the Wither or back of the horse. Your horse may have a long Wither. This means it may need a wider gullet. Your horse may have a high Wither. This may mean that he needs good clearance in that area which could entail needing the saddle to sit higher on the back. Your horse may have gained weight, which means the gullet will need to be wider. A horse with very low Withers may need a shallower channel. It really does depend on your horse and the shape or weight he carries. If your saddle is ill-fitting on a three or four year old horse, it could cause damage to the top of the Scapula- the main bone used for movement. If your saddle does not have enough clearance for the spine and the Wither, it could pinch the cartilage of the Scapula. If this is damaged, it remains damaged forever. It does not grow back. It is your responsibility as the owner and carer for that horse to ensure that your saddle fits correctly.

These changes are subtle and may seem obvious to some, however the changes can often be great or even small and any change to the shape of the wither will affect how your saddle fits properly. That is where saddles that are fully adjustable work very well with your horse. Particularly if your horse competes a lot or your horse wears your saddle more than once or twice a week. Your saddle must be comfortable to the horse so that it does not cause any lasting damage to any muscles or soft tissue in your horse's body. For more information about how ill-fitting saddles can cause damage, tune in next week or perhaps read our article 'StrideFree in Newmarket', which shows the damage a poorly fitting half-tree saddle caused to a promising young thoroughbred.

Next week...

We will be taking a look at how the tree inside your saddle can affect your horse if it does not fit properly. Have a look at some examples of traditional trees with protruding points and compare them to the shape and results of our PHS StrideFree tree.