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?
The unpopular truth is that cows are meant to eat grass. Grains introduce a variety of issues that require active monitoring and management. Grain-fed dairy and beef feed the masses, but the niche market for grass-fed is active and growing.