A welcome addition to this issue of HORSES For LIFE and the subject of crookedness in our horses.

Asking questions about crookedness and the evolution of the horse that deserve to some serious attention and thinking.

The Unilateral Horse

What does unilateral development mean in relation to the horse?

By Bonnie J. Perreault (Jan 91/Dressage & CT)

What does unilateral development mean in relation to the horse? It refers to muscular, and possibly skeletal, development of one side of the horse’s body more than the other. In observation, we call the horse that’s capable of moving in one direction better than the other one-sided, stiff-sided, or unilateral. We usually make this judgement when we work a horse in hand, in harness, or under saddle and ask him to perform bends, turns, and circles. In one direction, he performs quite well and achieves flexion, but in the other, he resists, seems stiff, and has a definite problem doing what we ask.

How can a horse be unilateral?

There’ve been some interesting statements and theories on this topic.

In the early seventies, while in school at Porlock Vale in England , I heard the mane theory and was naïve enough to believe it. In 1987, I heard the same statement at the USDF National Seminar in Michigan and was quite surprised that it’s still given credence. The mane theory states that the side on which the horse’s mane falls will dictate which side will be hollow and which will be stiff. I suppose this could be a logical association, but I’d like to know how this applies to the Norwegian Fjord, or any other breed that has a naturally upright mane.

Another theory the reader may have heard is: how the horse is carried in the uterus will determine the unilateral tendency. This theory of fetal development was even mentioned by Wilhelm Museler in his book Riding Logic. As to actual scientific study, there’s been some recent research that’s disproved to some extent the thought that the early developing equine fetus is motionless. At the University of Wisconsin , with an endoscopic video apparatus, observation of actual developing fetuses was carried out on several mares from day 11 through day 78 of fetal growth. It was reported that the fetuses observed moved around a lot; they made swimming motions, did somersaults, and even changed location in the uterus. Nothing was concluded as to why all this activity is going on and what it means, but is should be interesting to follow this research.

The noted Austro/Australian author, Mr. Franz Mairinger, mentioned in his book Horses are Made to be Horses a theory about unilateral development that’s often stated: the horse is naturally crooked, with its hindquarters placed to the right, though there may be horses that naturally shift to the left. I should note here that horses, like humans, can be born with scoliosis, in which the spine moves sideways due to underdevelopment of one side of the spinal process. If both sides of the spine don’t develop properly, a foal can be born with a sway back.

The idea that a horse can be naturally crooked often gets confused with a theory that has to do with laterality: handedness. It hasn’t been proven in any scientific stuffy that a horse has a neurological predisposition for one side over the other. I don’t know why this statement has been made by several speakers at symposiums, but it’s only an assumption, and a poor one at that.