[tptacek]

This seems extremely unlikely, given the relatively small percentage of beef that comes from culled dairy cows, the absolutely vast amount of beef used as an input for fast food, and the named suppliers companies like McDonalds use.

[bee_rider]

I think they just mixed up their heuristic; fast food vendors always do the cheapest thing at scale, this is often sacrifices quality, but clearly the more economical thing to do is to kill and butcher the cattle ASAP. I mean why would they feed an adult cow for an extra year if they could avoid it?

[Detrytus]

The common practice is that you butcher bulls at young age, but you keep cows for milk - you actually make much more money on milk than on meat.

With chickens it's even worse: males are killed immediately after hatching, because their meat is worth next to nothing. Females are kept for both eggs and meat.

[kevinmchugh]

My understanding is that chickens are bred either for eggs or for meat. Egg farmers cull males as soon as they can (which depends on an interesting technical problem called sexing). Hens that can't lay anymore are called "spent hens", and the meat is not generally liked by Americans at least, so it's probably not what you're buying at the grocery store.

Poultry farmers raise both sexes and slaughter as soon as the bird is large enough.

[jcampbell1]

What? Cow meat is about 25% of the ground beef supply, with half being dairy culls and the other half being beef cows that fail to get pregnant. It ends up at McDonald’s, Taco Bell, and Beef hotdogs.

[tptacek]

The numbers I got were more like 9%.

You can also go to specific chains and look up their sourcing; Wendys sources from "steers and heifers", but all much younger than the average dairy cow cull age.

It's not that I have a high opinion of fast food beef. I just think it's unlikely that they could come close to meeting demand by sourcing from culled cows.

[jcampbell1]

Your 9% number is impossible as at least 10% comes from purely beef production. 25% of ground beef is old cow meat, and it isn’t sold at grocery store meat sections. It ends up in processed foods and fast food. It is legally beef, but that is about all you can say about it.

[tptacek]

Look, I honestly don't care --- I actually think it's laudable to put less commercially desirable meat to use, in the same way I think it's a good thing to use transglutaminase to stitch trim and offcuts into chicken nuggets --- but I can't find a single source that suggests culled dairy cows are a significant input to fast food. I can find direct statements from chains that preclude it. I've concluded that it's just not the case. We don't have to agree, but if you've got a source, I'll read it.