How now brown cow?

This phrase used to be used in elocution teaching to demonstrate rounded vowel sounds. It isn’t clear when it was coined or where. It was certainly known in the USA by 1942, although is probably earlier. The expression appears in an item in the Maryland newspaper The Capital, in February 1942:

“Laird Cregar, now contributing his booming voice to ‘Ten Gentlemen from West Point’: explains how he got it. When he first tried out for the Pasadena Community Playhouse his voice wouldn’t carry past the front rows. Coach Belle Kennedy had him declaim How, Now, Brown Cow? and The Rain in Spain Still Stains – over and over.”

The term Brown Cow had previously been used in Scotland as a jocular name for a beer barrel. Allan Ramsay, used it in his The gentle shepherd, a Scots pastoral comedy, 1725:

” The auld anes think it best With the brown cow to clear their een.”