"But it is not the animals/meat which are the target of antibiotics it is the microbials (bacteria etc.) The fact that the host animal is dead doesn't prevent any microbials present from building resistance to the antibiotics used. (assuming they are not all successfully killed) "

It is worth emphasizing that any animal treatment regime generally stipulates a minimum time period must elapse between cessation of treatment and subsequent slaughter.

For example: SUMMER DIP. use to treat and control Blowfly and Sheep Scab (Psoroptes ovis) in Sheep. Contains Diazinon (Dimpylate) 10% w.v. Excipient-solvent naphtha (petroleum) heavy aromatic mixture.

Withdrawal Periods :        Animals intended for human consumption must not be slaughtered during treatment. Sheep intended for human consumption may only be slaughtered from 35 days after the last treatment. Not for use on ewes producing milk for human consumption.

And we had best not talk about chicken shit once fed as a protein supplement to ruminants(and still is in places)