Handedness in Horses: Nature vs. Nurture?

Do horses naturally have a dominant side or is this something we inadvertently develop in them as a result of our riding and training? 

horse on lunge line

Many mammalian species, like people, exhibit a preference for using one side of their body over the other — and do so with greater strength, co-ordination and dexterity than with the less favoured side. Ever try writing with your non-dominant hand? It’s a slow painful process for most of us.

While we might be born with an innate preference (and the science suggests we are) – the way we develop physical and mental skills over time serves to reinforce our preference, making it even more pronounced the older we get.

But what about horses? Are they too born with a dominant side? And what happens when they meet us humans that not only tend to handle them asymmetrically, but have asymmetries of our own that get transposed through our riding?

Maybe she’s born with it?

… Maybe it’s Maybelline.

Recently, a group of Italian researchers set out to find out. Not if your horse is wearing make-up, of course, but whether or not foals and young horses exhibited a more dominant side BEFORE being influence by asymmetrical human handling.

In their study, they looked at a group of 46 horses – 29 nine-month-olds and 17 two-year-olds – that had all been handled bilaterally (equally from both sides) since birth. To test for motor laterality (ie, the presence of a more dominant side), they observed each horse in a round pen at the trot and noted in which direction, if any, they “derailed”, or cut the circle.

Horses that “cut the circle” (ie. were falling-in) to the right were considered right-sided (or right-lateralized) and vice versa.

Study findings

According to Pia Lucidi, one of the study’s authors, horses that cut the circle to the right (ie. were considered right-sided) also showed a natural bending to the left. “[They] show a natural flexibility to the left and the ability to bend correctly to the left. In fact, in a right-sided horse, the left hind leg is put well in underneath the body (engagement) while the right leg is unable to engage to the same degree but it pushes more, being the stronger hind leg.”

In other words, when a horse is right-sided, the right hind is the stronger of the two, but the horse actually travels better to the left. This tendency, according to the study, “would be due to the horse’s inability to put the right hindleg deep in underneath his body, to supply the necessary support for the flexion in the turn to the right.”

In terms of the development of laterality, the study found a much higher level of ambidexterity (nearly 70%) among the foals compared to the two-year-olds (35%). Interestingly, there was also a marked tendency within both groups, where lateralization was exhibited, for horses be right-sided.

Remember, for all horses in the study human handling had been completely bilateral, with the horses being young enough that training under-saddle had not begun.

What the researchers therefore concluded is that motor laterality (handedness) in horses develops over time, and, as with humans and many other animals that have been studied, is a naturally occurring phenomenon.

Significance

These findings underlie the importance of solid training to encourage straightness and balance in the horse. “We know that if a child is started in a sport such as fencing, he will use the dominant hand and, over time, he will risk having disharmonious growth and creating spinal problems. For this reason, fencers, tennis players, javelin throwers, etc, must undergo specific training to balance the two sides of their body,” explains Lucidi.

“The same is true for the horse,” she continues. “The horses’ natural asymmetry settles before their use in riding and can worsen under a bad rider. However, horses’ asymmetry can be contrasted by adequate training. A well trained horse is indeed balanced.”

 

Pia Lucidi, Giuliano Bacco, Marilena Sticco, Giancarlo Mazzoleni, Mariateresa Benvenuti, Nicola Bernabo, Roberto Trentini. Assessment of motor laterality in foals and young horses (Equus caballus) through an analysis of derailment at trotPhysiology and Behavior, 109 (2013) 8-13.

About Lindsay Day, REMT

Lindsay Day is a Registered Equine Massage Therapist and award-winning writer based in Ontario, Canada. She is a graduate of the two-year equine massage therapy program at D'Arcy Lane, and brings to her practice over 20 years experience riding and working with horses. With a strong commitment to promoting the health and welfare of horses through her work, Lindsay uses massage to help horses find ease of movement and comfort in their bodies, so they can feel and perform their best.