Green’s Dictionary of Slang

a dog, usu. greyhound, thus the cherries, greyhound racing.

a.1945		L. Payne private coll. n.p.: Dog Cherry ’Og.
1950		P. Hoskins No Hiding Place! 189/2: Cherries. Dog-racing.
1960		J. Franklyn Dict. of Rhy. Sl.
1969		S.T. Kendall Up the Frog 11: Take the cherry ’og for a ball o’ chalk up the frog and toad.
1976		(ref. to 1940s) R. Barnes Coronation Cups and Jam Jars 163: Keep that cherry hog of yours on that piece of string.
1992		R. Puxley Cockney Rabbit.