Steve, I learned the chorus from Ed Silberman as:

Hurrah for Mary, hurrah for the lamb
Hurrah for the Fenian boys who did not give a damn
And everywhere that Mary went, the lamb was sure to go
Shouting the battle cry of freedom

I have a suspicion that this song may come from the Civil War, and that "Fenian" may have originally been "Union". I'd be interested if anyone could confirm or deny that. It's been so long ago that I can't remember any of the verses that Ed sang.

Of course, this is not to be confused with:

Mary had a little lamb, the doctors were surprised
But when Old MacDonald had a farm, they couldn't believe their eyes

Aloha,
Mark