Hattie was spayed at just over 7 months (she was definitely bigger than 6kg though, probably closer to 10kg). It was a really tough decision but I don't think we made the wrong choice. Our vet said that he spayed after the first season for the first 10 years of being a vet and has recommended doing it before the first season for the last ten years and he hasn't seen any difference in the dogs he treats, including regarding incontinence. She was brilliant while healing, especially as she's a wriggly, roly, itchy, bouncy little dog, and I don't think that it's changed her at all