This week in Horse and Hound, the vet article looked at if winter really does cause depression in horses. Short days and a lack of sun can cause mood swings and low energy in humans, but is it possible horses can suffer in the same way?
Seasonal affective disorder (SAD) affects 8-10% of people living in northern regions. It is a recognised medical condition that brings about depressive symptoms and lack of energy in winter. Some horse owners believe that their horses are more lethargic in the winter months and less enthusiastic during ridden work. However, this statement is contrary to every experience i’ve ever had with horses in winter. Usually, the cold of winter and their clip brings them into a ‘mental’ phase, meaning that the calmest of horses will turn into a spooky extremely forward going horse.
It is most likely that when owners make these claims, the horse is suffering from something else rather than ‘SAD’. This can include pain from low-grade arthritis in the joints, exacerbated by the colder weather, or from other conditions such as stomach ulcers irritated by an increased amount of hay in their winter diet. Other elderly horses may be suffering from Cushing’s disease, which can cause lethargy in winter. However, in horses were these and others options have been ruled out, could they be suffering from winter depression?
Rhythms of life
Light is the most important environmental factor that controls the body’s rhythms. Its effects on animals that breed seasonally, like horses, is obvious. Along with the photoreceptor cells responsible for vision, the equine eye contains light-sensitive cells that transmit information via the optic nerve to the suprachiamatic nuclei within the brain. These nuclei lie within the hypothalamys and are more commonly referred to as the home of the ‘circadian clock’. It is the structure that oversees body rhythms, partly by determining the release of melatonin-a hormone that controls sleep patterns. In humans we can relate this to our own ‘body clock’. E.g, if we set an alarm for the same time each morning, your body will become accustomed to that time and you will find yourself waking up a couple of minutes before your alarm.
The variations in physiology and behaviour shown by horses and humans throughout any 24 hour period are known as circadian rhythms. While humans are ‘diurnal’ creatures-most active during daylight hours- horses are ‘crepuscular’ meaning they are more active at dawn and dusk. Relating this to my own horse, she is much more enthusiastic to go out for a training session at around 9am or 4pm, rather than in the middle of the day.
SAD in humans is clearly linked to disruption of these circadian rhythms, as winter approaches and the nights draw in. Rather than being able to follow their usual circadian rhythms, as they would in the wild, our horses are generally subject to human driven routine that may well be disrupted further by seasonal variation. Furthermore, prolonged periods of dark lead to increased levels of sleep-inducing melatonin. In humans, this triggers a reduction in serotonin- a lack which can cause depression. We don’t know for sure that the exact same process occurs in horses, it would seem logical to suggest that it might ad=nd this biochemical imbalance could induce similar SAD-like symptoms.
Light therapy, where artificial light is used to counteract darkness during winter months, has proved useful in helping SAD in humans. Little is known about the use of light therapy on the well-being and behaviour of horses, a study being led on on stabled horses by Dr Carol Hall at Nottingham Trent University; it produced interesting results. Horses in the trail were placed under broad-spectrum, high-intensity light, chosen to mimic daylight, for an hour every day for six weeks. Their behaviour before and after the trials was then compared with similar horses who had not received this light therapy. Blind trials were carried out so that the assessors recording the behaviour of the horses did not know which of them had been treated. The criteria recorded were feeding, behaviour, sleep patterns and the horses’ attitude to being handled and ridden.
Although this was only a small study, differences were noted between those horses exposed to the light and those who weren’t. Those who received light treatment showed no significant variation before or after light exposure in any of the areas measured in study. However, the untreated horses were found to be sleeping for longer and were described as lazier at ridden exercise at the end of the six weeks. The yard manager reported that the light-treated group were less grumpy.
Let there be light
The results suggested that keeping horses stabled for long periods-and thus exposing them to longer periods of low light or darkness- may well have the effect of producing SAD-like symptoms at any time of year. Studies in the USA have shown that if a stabled horse is taught how to turn the stable light on, he will; therefore showing that horses prefer the light.
There is an important factor to consider before using light therapy. The equine eye is adapted for low light levels and their vision is not as good as our in brightly lit conditions. As a prey animal, a horse’s eyes see best at dawn and dusk when its natural predators are most active. While this does not mean the horse needs less light we do in terms of hours per day, it does mean that strong lighting has the potential to cause discomfort. Dr Hall’s study, in addition with our own knowledge of how light affects the horse in other ways, would lend support to the idea that horses should receive light for a generous part of each day. Keeping them in darker environments for prolonged periods may not only represent poor husbandry in terms of quality of life and socialisation with others, bu could-in some ways- lead to SAD.
If depression is suspected and your vet has ruled out obvious physical ailments, exposure to more light may be a good place to start. While much work remains to be done, early studies and anecdotal evidence suggest that light therapy may be a useful tool for gaining optimum equine performance, year round.
Apologies for not publishing this article on Thursday evening as usual. I was not able to get the magazine on Thursday or Friday this week. More to come next Thursday!