The problem with feeding foals only hay or natural pasture is that both are deficient in nutrients essential for their proper growth and development. Crucial minerals such as zinc, copper, calcium and phosphorus are usually deficient or unbalanced in these forage feeds. Quality sources of protein are also necessary for the foal to grow healthily, so if the foal's diet is based only on pasture/hay, the protein levels will also be compromised and lysine, the limiting amino acid, will be deficient.
Providing a specific concentrated feed for the foals' growth phase, together with good pasture and/or hay, is therefore essential to ensure their correct development.