It is a common concern as to whether a horse needs be stabled during the winter and it can be easy to put human needs and preferences before the needs of a horse.
Horses are herd animals who are, in general, more resilient than we give them credit for. They can adapt successfully if they are given a chance to acclimatise to their surroundings. Horses evolved as a social species living in open plains where running away was their primary method of escape from predators. Today, horses still possess an inherent aversion to isolation and confinement.
Research has shown that horses with free access to both pasture and to box stalls with bedding, hay and water, prefer pasture even during poor weather as long as some grass is available.
Chronic frustration from isolation, lack of social contact, lack of environmental enrichment and/or lack of stimulation can result in abnormal or stereotypic behaviours (‘stereotypies’). Abnormal behaviours include pacing, licking, eating or chewing of non-food objects. Stereotypies are repetitive behaviours horses use to cope with the abundance of time that would otherwise be spent grazing and socializing. Examples of stereotypies include crib biting, weaving, wind sucking, head tossing and head nodding. Unfortunately some stereotypies become learned behaviours that cannot be resolved, even after the horse has been removed from the environment that initially triggered the behaviour (e.g. wind sucking).
If you are worried about turning your horse out in the cold, remember that it has a waterproof coat and a central heating system – the digestion of fibre generates a lot of heat, keeping horses warm from the inside out. For many horses, this will be enough to keep them warm throughout the winter. For those horses that are clipped or appear to feel the cold, there are all sorts of rugs available – you can even find ones which would keep your horse warm at -40°c!
If it is necessary to keep a horse stabled then the following should occur: ideally, where possible, the horse should be in hard work; it should also be on controlled rations and the stable should be big enough and have good ventilation. Try to ensure they have at least one other horse to interact with and a field to run around in for at least some of the day. Ideally at least 4 hours per day should be spent out of the stable, while able to move in all gaits.