Go to the Ensembl homepage www.ensembl.org. Click on View full list of all Ensembl species. Click on Cow in the table to go to the species homepage.

Under Other assemblies two previous assembly names and the releases you can find them in are listed.

Assembly UMD3.1 is available in the archived release 94 and assembly Btau_4.0 is available in the archived release 54.