Look at the date of manufacture on the bag. Its purported nutritional values will have been declining since then. If it is very old it's probably no better than sawdust. I also don't give medicines unless they are absolutely required. So I probably would raid the larder instead, and give the...
there are lots of suggestions for chickens here @chickenlady2004
https://www.backyardchickens.com/articles/wholesome-home-made-chicken-feed-without-sweat-tears-a-calculator-or-deep-pockets.78655/
That apart, as a short term fix to tide the chickens over until you can get new feed, you can...