Alfalfa hay is actually a good choice for feeding young growing horses and is actually GOOD for their bones! It is high in calcium and protein, two nutrients that growing horses need in higher amounts than other horses. Feeding young horses alfalfa can be done alone or as a mix with a grass hay (i.e., timothy/alfalfa mix or orchard grass/alfalfa mix). The high protein in the alfalfa will not cause growth defects like physitis, as used to be thought. The problems with growth have been more linked to mineral imbalances or high soluble carbohydrate intakes.