I don't see this being mentioned anywhere. But in the US and most of Europe, cows are lined up and shot (not exactly with a bullet but with a bolt) into their brain, making them continue standing stunned with their heart beating while their brain matter mixes with the blood. The blood with brain matter of course reaches several organs and tissues by the time the cow is killed and the meat is harvested. This to me is the worst way to kill a cow in terms of human health safety, though it maybe humane. The halaal/kosher way of killing the cow is much safer, but seemingly brutal. As a protein bioinformatics person I had an academic interest in the folding and stability of prions at some point of time, and they are very scary imo. I always wonder how much of a factor this is in the rise of amyloid diseases in western populations. I personally haven't ever eaten red meat at all, which I believe is the best thing. But if you are going to go for cow meat, at least this factor has to be addressed.
I often hear metabolism being pointed out. I am interested in metabolism as well and I think they maybe a factor as well, but through a different mechanism such as blood circulation and oxygenation issues.