Sorry to burst your bubble, but supplementing livestock is not for it's well being but to improve it's utility more rapidly than normal.
And not all farm wisdom is necesarily good as evidenced by the mad-cow disease epidemic to mention but one.
In nutritional studies it has been shown that it is still more effective to obtain the necessary vitamins and minerals from fresh fruit and veges.
Vitamins and minerals have been found to be absorbed differently according to the vector.
Also for me personally it is more satiating and pleasurable to eat something that fills the stomach and gives the necessary nutrition rather than pop a pill and still feel hungry