"I have my own cats."
Translation:Tengo mis propios gatos.
That's because the default gender in spanish for everything is male, and "gatos" is cats/male cats and "gatas" is female cats. Saying "Yo tengo mis propios gatos" could mean that you have 1) x number of male cats exclusively or 2) x number of male and female cats. Saying "Yo tengo mis propias gatas" means that you have female cats exclusively.
The simple fact that someone might have all female cats means they probably have a way to communicate that fact clearly. If there is a default gender in common real world use it is kind of irrelevant in a learning situation where you must learn the ability to communicate every possibility clearly.