Chilli Morning (pictured) entered the record books with his Badminton CCI4* victory last month, becoming the first stallion to achieve this feat.

Stallions frequently reach the top levels of dressage and showjumping, but why are they so rare on the eventing scene?

There are few advantages to keeping a competition horse entire — unless you want to breed from him, in which case his testicles are essential, unless artificial insemination is used with stored semen and the horse is gelded. Stallions are often more difficult to manage, typically require more feed, care and attention, and are likely to cost more to keep.

It is true that stallions develop more muscle, so they have a different appearance to geldings and mares. It is also recognised that colts can grow faster than fillies, which is one of the reasons why young thoroughbreds do not have to race against each other and why fillies can carry less weight when racing.

Many people feel, however, that this is muscle mass and growth rate is irrelevant.

Certainly by the time that horses are ready to compete in eventing, any advantage of having testicles is long gone.

Typically, colts are castrated after the point at which they are mature and there is no further real gain to be made — so a gelding does not usually lose any of the “advantages” he may have had as a stallion. If anything, stallions are likely to be heavier and perhaps less athletic with less stamina, so may be less suited to the rigours of eventing.

In addition, stallions are easily distracted. Their main focus in life is to breed with mares and not necessarily to produce a foot-perfect dressage test, which can make them more difficult to train and compete.

Undercarriage at risk

The presence of testicles can make stallions less willing to jump large obstacles.

Brushing through the top of a birch hedge or sliding off the log and drop into the Badminton lake could cause serious trauma to the testicles. Hence the scarcity of national hunt sires — very few stallions are able to prove themselves over fences.

Due to the thin skin and a rich blood supply, blunt trauma to the testes can cause haematomas (large blood blisters). These can be very painful and may need to be treated with surgical drainage and lavage (flushing out) of the scrotum.

Another painful condition of the testicle is spermatic cord torsion, which occurs when the testicle twists about its axis. This interrupts the blood supply and can cause testicular congestion — a condition requiring emergency treatment.

Stallions are also more prone to inguinal herniation, which is when the abdominal contents gain entry into the scrotum. This is more common during exercise and requires corrective surgery, often as an emergency.

Alongside these sometimes life-threatening conditions, the biggest risk to the stallion is permanent damage that can significantly reduce his breeding potential.

One of the main reasons why a stallion would compete to a high level is to increase his value as a sire, but with that comes the possibility of injury.

Ref: Horse & Hound; 4 June 2015