Green’s Dictionary of Slang

(US) a scraggy cow or other animal fit only for the lower end of the canned meat market.

1892		Pall Mall Gazette 8 Dec. 2/1: ‘Canners,’ which is the designation of all animals collected at the Chicago and other markets that are refused by the butchers as unfit for their trade [DA].
1893		Mexico Wkly Ledger (MO) 23 Nov. 3/3: All kinds of cattle $everything rom a ‘canner’ cow to the finest export steer.
1903		Mt Sterling Advocate (KY) 25 Feb. 1/4: Who are those fellows riding those ‘canners’ (poor horses) up and down the street?
1907		Chicago Eagle 21 Dec. 1/3: The canner cow is a scandal [...] Canners are sold in drove to Packers who make ‘Delicacies’ out of them [...] A canner cow is a poor, worn-out diseased or emaciated animal.
1911		H. Quick Yellowstone Nights 303: A collection of skips an’ culls an’ canners that was sure a fraud on the Injuns [DA].
1922		Columbian Eve. Missourian (MO) 11 Dec. 8/1: yearling cows and canners.