Over a certain amount per species, you are no longer considered a regular owner of pets, but holder of a collection, a breeder or a refuge.
This is called a ´núcleo zoológico´ and you must apply for a special licence. First you need to check with your Town Hall on the local ordenance on the max. amount of domestic animals you can keep per species, say dogs.
This varies from 2 to 8 from what I´ve been able to find researching this subject and tend to differ depending on the denomination of your property, urban or rustico.
The only exception is for litters, while the pups are under 2 months old.
Towns may set their own limits with regards to maximum amount of pets, whether dogs or cats, so it´s always best to check for the local ´ordenanza sobre animales de companía´ at your Town Hall, before you decide to keep more than 2, to be on the safe side. Remember that if you are denounced for keeping more pets than allowed in your town, you can be forced to give them up, either relocate them yourself, or have the local authorities take them.
If the location of your property and the local ordenance allow you to apply for a licence for a ´núcleo zoológico´the next stop would be your vet, to help you with the forms for the licence application and where to send them.
For government websites for full information on the registration of ‘Núcleos Zoológicos’, use those words plus your region to search with google.
Feeding of abandoned animals. Most towns have strict regulations clearly stating that cats or dogs who have been abandoned or are wild, must not be fed in the streets. There are fines for those who do so.