What negatively impacts a horse's ability to cool itself through radiation?

Covering a horse with tack or a cooler can significantly impede its ability to cool itself through radiation. Radiation is one of the primary mechanisms by which a horse loses heat—essentially, it radiates heat from its body into the surrounding environment. When a horse is covered with additional layers such as a cooler or tack, it creates insulation. This insulation traps heat close to the horse's body, reducing the effectiveness of heat dissipation through radiation. As a result, the horse may struggle to maintain an optimal body temperature, especially after exercise or in hot weather.

In contrast, other factors such as exercise levels, water intake, and breed type, while important for overall health and performance, do not directly impact the process of heat loss through radiation in the same immediate and critical way that covering the horse does. Therefore, the presence of external coverings is particularly detrimental to the horse's natural cooling processes.