Feeding the Growing Horse for Health and Performance

You chose both the mare and the stallion and you waited almost a year during the gestation of your anxiously anticipated foal. Now the foal is here and approaching the age to wean. The mare has done an admirable job of supporting that young life for the past 15 months during pregnancy and nursing but now you must take over the task of meeting the nutritional requirements of your growing horse.
The successful feeding of young horses postweaning demands that we meet their nutritional needs for maintenance as well as for growth and development and as they get older there may be nutrients required for work.

Failure to meet the nutrient needs of growing horses can restrict their development and may affect their productivity later in life. Good nutritional guidelines for growing horses have been established in the National Research Council Nutrient Requirements of Horses NRC and there are plenty of manufactured supplements and feeds for growing horses available. So feeding that young horse should be easy right? Not always! Genetic factors forage quality and management are all significant contributors to the development of a successful feed ration for the growing horse. How do you get it right? 
The Importance of Balance
Growth in young horses is multifaceted and consists of bone growth development of soft tissues and weight gain. A critical aspect of healthy growth in the young horse is skeletal development. Balanced nutrition is a fundamental aspect of healthy bone growth. Weight gain that is in excess of what the developing skeleton can support will cause problems. Rations for growing horses must be balanced for essential nutrients without providing excessive energy and for all nutrients to permit good bone development without excessive weight gain.
What is a Limiting Nutrient?
Protein is an important nutrient but even more important is protein quality. Protein is comprised of building blocks called amino acids. Some amino acids are in plentiful supply in equine diets and some are not and so are called essential amino acids and must be supplied daily in the diets of growing horses. 
An example of an important essential amino acid in the diet of a growing horse is lysine. Lysine is a limiting nutrient in any equine diet that does not provide sufficient intake of it to support the growth requirement of the horse. In other words equine diets where lysine is a limiting nutrient will permit only as much growth and development