Every stock food manufacturer claims that his particular brand of food will give greater gains or cheaper gains when fed in addition to a ration than that ration will give when fed alone. This claim is based upon the assumption that the spices, seeds, barks, roots, and herbs of which each food is said to be “scientifically compounded,” either directly stimulate the glands of the stomach and intestines which have to do the work of digesting and assimilating the ration; or else that the compounds act indirectly on these glands by toning up the entire animal system, purifying the blood, etc.*
Michael, Louis G. and Kennedy, W. J.
"Influence of condimental stock foods on the digestibility of a corn ration fed to swine.,"
Bulletin: Vol. 10
, Article 1.
Available at: https://lib.dr.iastate.edu/bulletin/vol10/iss113/1