The earliest to transition to Integrity Growth is 10-12 months. Foals by that age have developed the molars for chewing a texture/multiform feed as Integrity Growth. Mare & Foal is higher in the amino acid lysine, slightly higher protein, and has less fiber than Growth. Also, Mare & Foal is a pellet and does not contain beet pulp which may provide some advantage with chewing and consumption during the growth phases after 12 months. My preference is to continue with Mare & Foal to at least 18 months.