Have you ever wondered if your horse feels cold at the same temperature as you?
Thermoregulation is the physiological process which balances metabolic heat load and the exchange of heat with the environment.
Horses are endothermic, meaning that they can produce heat through metabolic processes in the body, despite changing environmental conditions. All animals have a thermoneutral zone, which is the temperature range that requires no energy expenditure to maintain. So what happens when the temperature moves outside of this zone?
How does the horse cope in cold weather?
The human thermoneutral zone is much narrower than that of the horse. For the human, the optimum ambient temperature to maintain thermoneutrality is approximately 21°C. Horses, however, can maintain thermoneutrality between 5 and 25°C. So when it’s 10°C and we feel cold, our horses are probably fine!
They have various way of managing their own temperature to keep warm during colder conditions.
Horses are hindgut fermenters, with the hindgut having the propensity to produce an enormous amount of heat. One of the best ways to ensure that your horse keeps warm in winter is by providing them with adequate forage.
Piloerection is the process by which the horses hairs raise, trapping more air and increasing the insulation provided by the coat. A dry coat has a much higher ability to insulate than a wet coat.
The horse is also able to vasoconstrict their blood vessels in the skin and extremities, to minimise heat loss from the surface. Conversely, they are also able to vasodilate, increasing blood flow and warming the skin to increase heat loss. This is one of the main methods that the horse uses to maintain the core body temperature within narrow limits.
Shivering, whilst not always nice to see, is another way in which the horse produces heat. Shivering has been seen to increase heat production by a factor of five within seconds.
How does the horse cool down when it’s hot?
Horses begin to struggle when the temperature exceeds 25°C. A recent study found that the incidence of exertional heat illness in horses can increase by 28.5% when the temperature goes beyond 28°C – a progressive increase in this is expected as a result of global warming. So what does the horse do to manage this?
One of the main ways that horses cool down is by sweating – they can produce three times more sweat than a human.
As mentioned previously, the horse is also able to vasodilate, maximising blood flow to the skin to help dissipate heat. This can, however, have detrimental consequences in extreme cases as blood flow to the brain and intestine is decreased.
Can this differ between horses?
Of course, horses that are older or have health problems might deal with temperature change in a less effective way than younger, healthy horses. But what about differences across breeds? We all know that native breeds seem to cope better in bad weather, but is there any research to quantify this?
Interestingly, yes. Various studies have found that there are differences across breeds in thermoregulatory processes. One such study has found that Spanish breed horses tolerate heat stress better than Friesian horses when exposed to winter tropical conditions. It has also been found that different breeds have different lower critical temperatures (LCT) – the lower end of the thermoneutral zone. One study for example, found that Standardbred trotters that were acclimatised to 15-20°C had an LCT of 5°C, whilst the LCT of some Quarter horses has been estimated to be as low as -11°C in horses acclimatised to temperatures between -15 and +10°C. These studies are however outdated and more research is needed to determine whether this was a result of the environment or breed characteristics and genetics.
References
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