Horses have a natural ability to adapt to changes in environmental temperature 1. When they are exposed to colder temperatures for an extended period during winter, their bodies adapt through the process of thermoregulation 2.
A horse's body temperature is regulated through a balance between heat production and heat loss to the environment. When the ambient temperature decreases, receptors located in the skin and other tissues send signals to the hypothalamus 3. These signals trigger physiological adaptations that help the horse acclimatise to colder conditions. The skin reduces heat loss by decreasing blood flow to its surface 3. In addition, the hairs of the winter coat stand erect, trapping a layer of air that improves insulation and helps retain body heat 4.
Body heat is generated through various metabolic processes, including the digestion of nutrients within the digestive system. These metabolic processes require energy supplied by the diet to produce heat and maintain body temperature 5,6. As environmental temperatures decline, a horse's nutrient and feed requirements increase in order to maintain normal body temperature 6.
Forage contains a high proportion of fibre, which is fermented by microorganisms in the hindgut to produce volatile fatty acids 7. The fermentation of fibre generates heat, providing the horse with an internal source of warmth that contributes to thermoregulation 8. In contrast, the digestion of starch from concentrate feeds produces relatively little heat because starch is broken down enzymatically, a process that generates minimal heat 9. For this reason, it is essential to provide horses with sufficient forage throughout the winter months.
As forage forms the foundation of the equine diet, it is generally recommended to provide forage at 2–2.5% of the horse's body weight per day. For a 500 kg horse, this equates to approximately 10–12.5 kg of forage daily. When temperatures fall below freezing, it is recommended to increase forage intake by 10–15% to support the maintenance of body temperature 10.
Studies have shown that the feed intake of wild horses varies seasonally 11. During winter, forage availability declines due to reduced grass and plant growth, resulting in a lower voluntary feed intake 12. To maintain body temperature under these conditions, horses mobilise stored body fat as an energy source 11. These fat reserves are accumulated during autumn, when forage is more abundant. Research indicates that horses increase their feed intake during autumn compared with other seasons in order to build body fat reserves that can be utilised throughout the winter months 11.
Research has also demonstrated that the body weight of wild horses fluctuates seasonally, with the greatest weight loss typically occurring during winter 11,13. Therefore, it is recommended that horses enter winter with a slightly higher than normal Body Condition Score (BCS), providing additional energy reserves to support them throughout the colder months 10. Furthermore, BCS should be monitored regularly during winter to ensure that the horse's energy intake matches its energy requirements, helping to prevent both underweight and overweight conditions.
References
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