I have been feeding my goats Dumor feed since I got them. I have now stopped. Before buying any feed, always check the seal area, generally at the bottom where the ingredients/contents label is located, for the packaging date. TSC is notorious for over stocking feed, that is kept in NON climate controlled areas in their back room, and the feed can go bad after as little as 6 -8 weeks. I just opened one of the last 2 bags I bought from them to mix with my animal's new feed and found moldy clumps of pellets inside. This feed was bagged in early August. When I bought it, I had no choice at the time as I hadn't switched feeds yet, so could not adjust them to the new stuff. They have a 1/2 pallet of the same feed stacked 15' up on storage shelves in back that dates to early July. I refused to buy any of that as I knew/expected it would be below grade quality.
https://www.backyardherds.com/threa...ripes-and-grumbles.33505/page-555#post-570956
In proper climate controlled conditions, yes, feed can last longer and still be healthy and viable, but when the feed sits exposed to temps above 100° and high humidity, not so much. If you have a farmer's Co-op near by or other dedicated feed mill, contact them and tell them what you're looking for. The Dumor I was buying was $14.99 for 16% protein. I told TSC that was too expensive and I was going to buy elsewhere. I now buy and feed 17% protein @ $9.65/bag. I buy it 12 bags at a time as the feed mill/store is ~45 miles away. Even with the cost of gas I'm saving money and getting better feed. The bags I recently got on Oct 6th were packaged on Sept 26th (Think I recall). Very recently regardless, so I know they are fresh and high quality.
Though I have goats, I believe it's pretty much the same with sheep. The medicated feed is primarily for the babies as they are starting to eat pelleted feed, to help prevent coccidia outbreaks. Adults don't, or rarely need that and many who plan to eat the meat, don't want medications and antibiotics in the meat. There are withdrawal times after administering meds. Even though they say it's safe, I prefer non medicated feeds. I've never treated for coccidia and never had an outbreak or issue. This through 2 successful kiddings. Not a lifetime of experience, granted, but should I HAVE an outbreak, THEN I'll treat for it, not before. Just MHO. I DO however recommend the CD&T vaccination annually for adults and initial + booster for newborns.