Green’s Dictionary of Slang

moo-cow n.

also moo, moo-moo

1. (UK juv.) a cow.

[UK]W. Combe Doctor Syntax, Picturesque (1868) 50/2: The moo-cows low’d and Grizzle neigh’d!
[US] ‘Sweet Jenny’ in My Young Wife and I Songster 70: So farewell to the violets / And the moo-cows so brown.
[UK]Clarkson & Richardson Police! 322: Cattle-stealing ... Moo shifting.
[UK]E. Pugh City Of The World 71: And little moos wi’ calves heads made of veal.
[Ire]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.
[UK]Indep. Rev. 26 July 1: The ‘dead things’ are several baby moo-moos.

2. (US campus) an obese person.

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