Hi, I use to have 18 cats both -&+ and I had no choice but to mix them because I live in a one bedroom condo. To the best of my knowledge none of my - became +. Many of my + lived long enough to die because of problems that come with old age. And then some of them died as young as 3mos. of age. It never gets any easier, but I have been blessed with the number of cats that have passe thru my life
