It's absolutely essential to provide foals with balanced, nutritious feed. After all, young horses can't manufacture what they need out of thin air! Young Horse bones and tissues don't just magically get bigger. They have to be built from the nutrients supplied in the foal's diet.
Historically, young horses have gotten their nutrition from their dams' milk and the plants they browse in the surrounding environment. That's it.
Even today, horses living in the wild don't have tubs of grain or supplements available to them. Those are modern-day dietary conveniences that we provide to our beloved domestic horses.
This isn't to suggest we should go completely back to nature's way. Modern horse breeds, especially, can have higher nutritional requirements than their sturdier wild cousins. And if truth be told, wild horses may be more stunted and scruffy than they would be if they were receiving better nutrition.
Modern Management
But far more often than not, young horses are fed in a way that bears little, if any, resemblance to nature's way. Instead of a very gradual weaning process over 9 to 12 months, many foals are deprived of their mothers' milk at a young age. Emphasis is put on rapid growth, even "fattening." Future soundness can suffer as a result.
First, it is important to realize that young horses do not need grain per se. Overfeeding calories in the form of grain encourages very rapid growth. Between growth spurts, the calories are deposited as fat. Both rapid growth and excess weight have been identified as risk factors for a variety of developmental skeletal problems including osteochondritis dissecans (OCD), contracted tendons, and physitis (inflammation surrounding the growth plates).
If minerals are not available in the correct amounts and balance, bone quality can suffer as well. Splints used to be a problem with young horses when put into work at an early age. Now you can see them on a significant number of babies at yearling sales.
