How much Vitamin D per day do my Cornish Cross Chicks need.  I used  (years ago) to buy a small packet with Vitamin D plus electrolytes to put in their water.  I am overwhelmed with choices in the feed store with lots of stuff I don't think a small flock needs (such as probiotics) for daily use.

Please let me know recommendations for supplemental Vitamin D for Cornish Cross chicks.  Thank you