My lama here in Greece practices releasing animals in order to save their lives. A powerful practice that accrues imense virtue and benefit. This practice works best for animals that are to be killed (not that releasing animals destined as pets is not a beneficial practice). It doesn't have to be a cow, it can be a much smaller animal (for example snails, quails and frogs that are being raised and sold for consumption). Smaller animals are easier for those living in cities. Live marine animals (fish, shellfish, prawns and crabs) is another option. Many fishing shops sell live bait which you can buy and release.
For those who want the practice I have made an electronic copy of The Essence of Benefit and Joy: A Method for the Saving of Lives
written by Jamgon Kongtrul and Loro Thaye. It's a 20mb zip file. Those who want a copy can PM me with their email address.
There are some other pracitces available on the net based on Avalokitesvaras six syllable mantra.