The qualifications required to gain employment in animal care are dependent on the exact role you are interested in. However, as a minimum, most employers expect you to be educated to GCSE level.
For volunteering, it would be advantageous that you obtain some form of qualification in animal care. For paid roles such as veterinary support assistants, zookeeping or working with animal charities, a qualification will be invaluable due to how competitive these roles are.