Management and Feeding of Horses in Cold Weather
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Although horses are very adaptable to cold weather, they must be managed sensibly during winter. A basic review of energy (heat) exchange in the horse will help to explain why certain management practices are necessary during cold weather. The easiest way to understand the impact of cold weather on a horse is based on the heat (energy) balance equation. Heat or energy balance is the difference between heat loss and heat gain over time. If heat gain exceeds heat loss over time, the horse will gain weight. If heat loss exceeds heat gain, the horse will lose weight. The most important loss of heat in cold weather is to the environment. Warm objects lose heat to the environment whenever air temperature is colder than the object. Horses, whose skin temperature is about 30oC, will lose heat to the air around them whenever the air temperature is below 30oC. The colder the air around the horse, the greater the heat loss will be. The main source of heat gain is the energy (calories which convert to heat) obtained from feed. Other minor sources of heat gain are muscular activity, the sun and mechanical heat in barns.
Horses respond in two ways to cold: acutely (immediately) and chronically (adaptive or acclimatization). The immediate response of a horse to a sudden change in temperature is to change its behaviour. Horses will seek shelter from the cold and wind, or huddle together, to decrease heat loss. Horses stop foraging and stop moving to conserve energy. Horses in cold, windy conditions typically stand with their heads away from the wind, their tails set low and into the wind. Shivering and other voluntary muscular activity can generate substantial body heat. It is not unusual to see horses running in cold weather. The muscular contraction involved in physical activity, such as running, results in heat production. In the dissipation of this heat, the horse's inner body core (heart, liver, intestine, etc.) is warmed. Thyroid hormone secretion is increased during sudden cold exposure in adult horses, but this response is short-lived. Horses will also vasoconstrict (reduce) blood flow to the extremities, such as the lower legs, the ears and the muzzle, and their hair will stand up (piloerection) to effectively increase the haircoat depth.
Horses exposed to constant chronic cold weather acclimatise to the cold. Typically, horses require 10 21 days to adapt to cold. For example, a horse kept at 20°C and exposed to temperatures of 5°C will adapt to temperatures of 5°C over 10 to 21 days. When the temperature drops to 5°C, the horse will need another 10 21 days to adapt to this increasing cold. This process continues up to 15°C, which is the lower critical temperature (LCT). Once the LCT is reached, physiological changes and human intervention, such as shelter and/or extra feed, are needed to help the horse cope with the cold. One of the physiological changes is an increase in density and length of the horse's coat. Body temperature and respiratory rates decrease to conserve heat/energy. The temperature of the lower legs, ears and muzzle decrease because blood is shunted from the extremities to reduce surface heat loss.
The horse's ability to adapt to cold depends on the duration of the cold weather and on the horse's energy intake. The latter factor, energy intake, is the most critical in determining how readily a horse develops a tolerance for cold. Horses lose weight if they do not eat enough energy to offset the heat loss to the cold surrounding air. Enough feed and good-quality feed are needed to supply adequate energy intake for the horse. Fat horses are able to mobilise some of their fat deposits as energy during cold snaps but enough good feed is the main solution for keeping horses in good condition through winter. Well-fed horses adapt without problem to cold weather, whereas unfed horses lose weight and lose cold tolerance. Yearling horses fed a high quality diet free-choice are able to tolerate temperatures as low as -11°C with no ill effect. Horses will generally eat to meet their energy requirements. In cold weather, feeding good quality hay free-choice is the simplest way to ensure that the horse will meet its energy requirements.
Various factors affect the ability of a horse to withstand cold. Large bodied horses, e.g. draft horses, are much more able to withstand cold because of a lower relative body surface area per unit of weight (area:weight ratio). Belgians are more cold tolerant than Thoroughbreds. Newborn foals have very poor cold tolerance. Horses up to one year of age are less cold tolerant than adult horses. In late pregnancy (9th month and beyond), energy requirements of mares increase and, consequently, cold tolerance decreases. However, a winter-adapted, well-fed, pregnant mare is at no higher risk than a gelding. Poor teeth, parasites and disease also decrease the cold tolerance of horses.
Horses kept in a shelter (shed) can conserve up to 20% more body heat than horses kept in an exposed area. A three-sided shed is suitable protection from cold winds and snow. A typical shed should be 8 metres deep and should provide an area of 7.5 - 9 m2 per horse for lying down. Adequate bedding, preferably straw, should be provided in sheds, especially for young horses. Well-bedded bluffs, coulees and treed areas can serve as alternatives for sheds. Animals that are able to lie down can reduce surface area heat loss by 20 25%.
Dietary energy is the only nutrient that must be increased for horses kept at temperatures below their LCT. The LCT for growing and adult horses in Canada is 0°C and -15°C, respectively. Maintenance energy intakes of adult horses must be increased 2.5% per Celsius degree below temperatures of 15°C or the equivalent of 2% more feed. Feeding good quality hay is the easiest and most suitable way to supply additional energy for idle, adult horses kept outdoors in cold weather. Horses will increase their voluntary feed intake if permitted. Horses can be fed hay free-choice without fear of producing laminitis (founder). However, owners who are limit-feeding their horses should ensure that 2% more feed per degree below -15°C is available to their horses. Groups of horses housed outdoors should be fed in a way that reduces competition among horses. Grouped horses typically have a pecking order for feed and space. Often, timid horses will become thin, even if plenty of feed is available, because the dominant horses in the group won't allow them to eat. Any type of feeder, including feeding on top of clean snowy areas, can be used, as long as enough individual feeding space (3 15 metres between horses) is available for the horses in the group. Feeders are preferable since they will reduce feed wastage by 25%. This is especially true of those with a floor in them. Salt and mineral should also be provided. Clean fresh water should always be available to horses. Snow is an unsuitable substitute. A horse would have to consume ten times its water requirement in snow to meet its needs. The horse would then need to use energy to raise the temperature of the snow from the outside ambient temperature to the horse's body temperature of 37° C. This is a huge energy drain and, when coupled with poorly digestible hay, can lead to gut impaction.
Winter pastures should not be relied upon to provide the sole source of nutrients for horses since they are usually poor feed sources for overwintered horses. Not only is the nutrient quality poor but, in deep snow, the maintenance energy needs of horses can increase by 40% because the horses have to crater or paw through the snow to find low quality feed.
The cost of weight loss in the horse is much higher than most people realise. Thin, malnourished stallions lose their ability to produce sperm. Thin mares have a very low conception rate. Underfed weanlings can become permanently stunted. Finally, the extra cost of feed needed to rehabilitate a thin horse back to normal will equal or exceed the cost of the feed that should have been given to the horse to maintain its body weight. Feeding horses is costly; not feeding horses is more costly.
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