Feeding Cornish cross
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What specific medication is listed on the tag? There are a few different ones used in poultry feed - one of the most common ones seen in medicated starter is Amprolium, do you see that on the tag? Are you raising/processing for your own consumption or for distribution?
Here's the thing about amprolium - there really isn't an official withdrawal time documented for it in meat birds because the way the meat birds are raised in the large industrial setups precludes the need for preventative dosing through feed. That being said - for personal consumption birds it would be a matter of making a choice for yourself/your family. Amprolium itself is a thiamine blocker - whether the levels at which it may be present in the meat would be an issue or concern is something you have to decide.