(uncountable) The lowest grade of flour in milling, secured largely from the germ or embryo and adjacent parts, and mainly useful as animalfeed.
1918, Alonzo Englebert Taylor, War Bread, New York: Macmillan, p. 75,
This fraction of grain offal contains a number of over-lapping sub-fractions, which are known in the trade as red-dog, shorts, middlings, and bran. A portion of the red-dog is contained in the lowest grade of straight flour.
Verb
reddog (third-person singular simple presentred dogs, present participlered dogging, simple past and past participlered dogged)