I was shocked to read that eggs generally have pleasing deep-yellow or orange-red yolks because the egg industry spends a lot of money to put special additives into chicken feed just for that purpose. There's no other benefit from those additives.
Mine have that colour because they eat a lot of weeds and vegetables. The only thing they eat which isn't food scraps or something that's lying around the garden is shell grit, quite literally ground up sea shells to make sure they have enough calcium for their egg shells. Don't always assume that it's an artificial thing, what they're emulating is a natural process. It really is a pleasure to see happy hens roaming around too, even if they didn't lay breakfast and cake material.
Prions are in brains, not eggshells. Mad cow disease was caused by cows eating the crushed up brains of other cows, which is in itself a charming illustration of the ethics of our industrial food system.
Prions are misfolded proteins; while prion diseases occur in the brain, I do not know of any evidence that the prions themselves are not found throughout the nervous system. Are they in fact isolated to the brain?
(Long after the fact, so probably missed the boat. Also, I'm Not An Expert on This, so grains of salt, etc.)
My understanding of Mad Cow was that the prions involved were ones which were allowed to pass the blood/brain boundary, which keeps arbitrary chemicals in food from having a big effect on our neurological state. (Drugs like MDMA imitate certain chemicals used by the brain and are thus allowed to pass by.) One of the reasons cannibalism - especially when brains are involved - is that the brain proteins look like your brain proteins, and are thus expected to be on the 'brain' side of the boundary. So when cows eat dead cow brains, they get serious neurological diseases, just like human cannibals are known to. Prions may be arbitrary bad proteins, but they're especially problematic in the case of eating brains.
Interesting. I've never heard of anyone having that issue. Honestly, I'm just doing what the old timers tell me they did. I've not seen any detrimental side effects but now I'm going to do my research.
Well, they're responding to what people like. Additionally, they have to compete with the "natural" and "organic" trend. If they didn't try to make their eggs look like whatever people/society currently deem normal then the "natural" and "organic" competitors would have successfully manipulated the market. And we'd all be eating overpriced food that probably only has the added benefit of looking like what we think natural food should look like.
http://shkrobius.livejournal.com/375927.html
I think about that now every time I see a pleasing, healthy-looking, tasty-looking deeply yellow yolk on my plate.