The word Alfalfa is believed to be derived from Arabic, meaning "best fodder". Based on archaeological finds, it is believed that Alfalfa hay was first cultivated in Iran, around 700 BC.
Alfalfa is considered to be a legume hay, containing 15-20% protein, based upon the growing and baling process. You have to be careful with horses around fresh Alfalfa, as it can be too "hot" (contain too much energy and protein) for them, and cause health issues. "Hot" cuttings of Alfalfa are generally fed to cattle, as their systems can better digest the higher protein content.
Horses can digest nearly 55% of the nutrients in Alfalfa, which includes protein, Calcium, and Phosphorous.