good points. My first thought in response to your posts was our meat herds. Cattle, especially, are fed grains (and grain fractions, and various byproducts from food processing) for finishing. I'm curious about how much of that, if any, is imported.
My vet a year ago told me, after a steer fed a 14% steer grower ration died from Vit B deficiency, that if I wanted to have healthy cattle, I would need to feed supplemental brewers yeast to my cows. Seems possible the vet already knew something was up. Isn't that an effect of aminopterin?