No, I do not know. Mine eat a good amount each day as well. They have access to the alfalfa free-choice (all they want) plus other options like layer pellets, scratch and BOSS. Problems might be realized if I come up short on other options and birds attempt to compensate by eating more...
Alfalfa, like many forages chickens consume, can contain toxins that if consumed in excess can cause health problems for chickens. The same plants can beneficial in lower amounts. Think coffee for humans. Plants can also vary in toxin content with variety, parts consumed and growing...