Green’s Dictionary of Slang

1. (UK juv.) a cow.

1812		W. Combe Doctor Syntax, Picturesque (1868) 50/2: The moo-cows low’d and Grizzle neigh’d!
1868		‘Sweet Jenny’ in My Young Wife and I Songster 70: So farewell to the violets / And the moo-cows so brown.
1889		Clarkson & Richardson Police! 322: Cattle-stealing ... Moo shifting.
1912		E. Pugh City Of The World 71: And little moos wi’ calves heads made of veal.
1916		Joyce Portrait of the Artist as a Young Man 1: Once upon a time and a very good time it was there was a moocow coming down along the road.
1999		Indep. Rev. 26 July 1: The ‘dead things’ are several baby moo-moos.

2. (US campus) an obese person.

1990

Eble Campus Sl. Apr. 6: moo-cow – obese person.