This is probably a stupid question but I'm worried. My 26 chicks are a little over a week and half old and growing FAST. I have been buying the Purina SunFresh Medicated Start & Grow (it is all my local feed store offers) and I have been buying it in little 5 lb. bags with a best by date on them. They are eating so much more now, I had to switch to a 50lb. bag. My question is...the 50 lb. bag has a date on the sewn on tape end that just says 7/18...Is this a use by date or a manufactured date? I'm asking because the feed from the little bags was a light golden color and the feed from the 50 lb. bag is a much grayer color so I'm worried that it is a use by date.