Feeding the foal or young horse can be tricky and will depend on individual circumstances, compliance of the mare and quality of the mare's milk. Nutrient requirements of young horses are extremely high, compared to those of adult horses, owing to their very fast growth rate. Protein requirements are high as a result of the rapid growth of muscle, connective tissue and other body parts. Calcium and phosphorus requirements are also high owing to rapidly growing bones. Carbohydrates are in high demand owing to the foal's high metabolic rate and energy requirements. These nutrient sources are all present in the mare's milk.