I now thaw the meat before feeding because I worry about broken teeth- other than that, they could, and would, happily eat it frozen- just takes a bit longer to get through it. If you are sending livestock to the butcher you should definitely get ALL of the scrap back from your animals, and maybe they would give you more as well, from other animals, especially if they are just sending it all to the renderer for free. It doesn't hurt that you are a customer.
One caveat- my vet does not approve of feeding pork to the dogs. She's okay with just about any other kind of carcass, including road kill! But, she thinks that pork can be too fatty and increases the risk of pancreatitis. I know that a lot of owners do feed pork with no problem, but we avoid it.
Tripe is actually the stomach content and you might be able to just get the entire stomach(s) and clean them out yourself. Stinks a bit, but other than that, not a bad job. My dogs would eat the entire stomach, contents and all, but they are so big the dogs can't get through them in one sitting, so I divvy up the tripe and cut the stomach into chunks which I can then parcel out.
The butcher cannot process horses- that you would have to do yourself as it is now illegal in this country to do it commercially. You can process all you want for your own use, but you cannot sell it nor charge to process for anyone else.
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