The law requires all horses, ponies, donkeys, mules and zebras to have a passport and the correct ownership to be recorded within 30 days of any ownership transfer on the Governments Central Equine Database. This has been law since 2005 but since then the law has been updated several times. Now all equines in England and Wales will be required to have a microchip linked to their passport. This means passports issued before July 2009 may need updating.
There are variations in the law depending on whether you live in England, Wales, Scotland or Northern Ireland. In each case you will need to read Commission Regulation EC 262/2015 as well as the legislation listed for your country.