Stringsinger: It was not Louis Armstrong who made the "horses" remark. It was the Georgia/Chicago blues musician Big Bill Broonzy.
I don't know how the quote got attributed to Louis but it ain't right.

A bit of research suggests that may have been both, although the remarks were phrased rather differenty. Broonzy's quip was in response to a question from Studs Terkel during a broadcast. The Armstrong version, which is the closest in form to that usually quoted by people, is attributed by Oxford Dictionary of Quotations to a 1971 edition of the New York Times.

If that's the case, then Mr A gets credit for the oft-quoted version, but Big Bill must get credit as the likely originator of the concept as he had been dead for some years by the time Louis piped up.