.Just as humans can be right or left-handed, so horses can show a preference for using one side of the body. This bias towards one side or the other is known as lateralization.
Identifying whether a horse is left or right -handed may allow the trainer to decide on the type of work to which it might best be suited. For example right-handed horses might be more successful, and less prone to injury, when competing on right-handed tracks. Some cross-country courses might prove better or safer for left-handed horses or right -handed horses. On the other hand, disciplines such as dressage and cutting , with their emphasis on balance, may be more suited to horses with no preference.
A recent study by Dr Paul McGreevy, senior lecturer in Animal Science at the University of Sydney, and Professor Lesley Rogers, Professor of Neuroscience and Animal Behaviour at the University of New England in New South Wales, assessed the extent of lateralization in both motor and sensory function in horses. A report of their work was published in Applied Animal Behaviour Science.
The first part of the study involved 106 Thoroughbred horses. Every minute for at least two hours, the researchers observed the horses while they were turned out in pairs in a paddock. They recorded three mutually exclusive activities: standing; flexing one or other hind leg; and moving.
The most common activity, recorded in 64% of the observations, was standing with the feet flat on the ground - either grazing, with one fore leg in front of the other, or standing square. Standing with one hind limb flexed occurred less often (22%). Horses were observed moving less frequently (14%). Grazing with the front feet square was rare.
Most horses in the study did not have a preference for right or left - that is they did not consistently stand with the same foot in front. However, those horses that did show a preference, preferred to lead with their left fore leg. This bias was more obvious in older horses.
The researchers suggest this might be an age-related change or the effect of training. However, even the untrained foals showed a preference for grazing with the left leg forward, rather than the right leg.
Horses showed no preference for which hind leg was flexed. Neither was the flexed hind leg related to the preferred foreleg (if any). Foals stood with one hind leg flexed less frequently than older horses.
In the second part of the study McGreevy and Rogers looked at whether horses had a preference for which nostril they used to investigate a new smell. They held a bag containing a small amount of stallion faeces directly in front of each horse, and recorded which nostril the horse used to sniff it.
More horses used the right nostril to investigate a new smell than the left.
Some horses were involved in both studies. So the researchers were able to look for a relationship between motor and sensory laterality. They found no obvious association between limb and nostril preference. In an individual horse the presence or absence of left footedness appeared to be unrelated to any preference for using left or right nostril for investigating new smells. So the left or right bias in sensory and motor functions seems to operate separately .
Motor activity - such as placing the forelegs - is controlled by the brain on the opposite side of the body. So movement of the left leg originates in the right half of the brain. On the other hand, the sensation of smell passes directly from the nostril to the olfactory lobe of the brain on the same side. McGreevy and Rogers note that the predominance of left bias in limb position and right bias in choice of nostril may suggest that the right side of the brain tends to be dominant in horses. But they point out that further studies would be needed before any firm conclusions could be drawn.
They also suggest that it is worth investigating whether the increased bias in older horses is influenced by training. If so, it might be possible to alter the training to encourage more use of the less favoured leg. This might help reduce wastage from uneven use, and might make racehorses more useful as riding horses once they retired from racing.
For more details see: Motor and sensory laterality in thoroughbred horses.PD McGreevy, LJ Rogers. Applied Animal Behaviour Science (2005) 92, 337 - 352.