Boy Howdy
Southern slang. An interjection. Often used as an expression of surprise for large quantities of something, or severity of something. See yessum.”Boy howdy! Them pumpkins sure are big! How’re we gonna carry ’em all, Ms. McGregor?”
“Boy Howdy” was the favorite expression of Lee Majors as Heath on “Big Valley.”
(via Urban Dictionary.)
Always loved “Big Valley” …