Which of the following factors does not influence a horse's nutrient requirements?

The factor that does not influence a horse's nutrient requirements is coat color. Nutrient requirements for horses are primarily determined by physiological and activity-related factors rather than physical appearance traits like coat color.

Body weight is crucial because larger horses generally need more nutrients to maintain their health compared to smaller ones. Age also affects nutrient needs, as growing foals, mature horses, and older horses have different dietary requirements to support their specific life stages. Similarly, exercise level plays a significant role in determining a horse's nutrient needs. Horses that engage in regular work or performance will require higher levels of energy and nutrients to support their activity.

In contrast, coat color is a superficial characteristic that does not directly relate to a horse’s health or nutritional needs. Therefore, it has no bearing on determining how many nutrients a horse requires.