if I wanted to have healthy cattle, I would need to feed supplemental brewers yeast to my cows. 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.
You are exactly right and this feeding an inappropriate diet to cattle makes the cattle industry the second largest consumer of "tum" in order to keep the cows in feed lots from having stomach upset, getting tense as a result and creating tough meat. The imbalance created by feeding grains vs grass is one reason heart disease is rampant in this country -- grains are high in Omega 6 fatty acids so the meat which used to be high in heart-healthy Omega 3 is not loaded with unhealthy Omega 6. To compensate people have to take Omega 3 supplements...
Then there is fish -- used to be high in Omega 3, but today so much is farm raised on the equivalent of dog food and also loaded with Omega 6's....