Where and how did you find this information ?
From the International Zoo Yearbook.
The one I am reading at the moment is volume 13 (1973) which records births of American Moose at Madison (USA) 1.2 ; Milwaukee (USA)1.0; Quebec (Canada) 1.0
In Europe thy were recorded as breeding at Rotterdam (Netherlands) (1 D.N.S.) and Whipsnade (GB) 1.1