Hello UK, They can come into heat "usually" from 8 months to 12 months for the smaller breeds. Then the next heats might even change from the 8 - 12 months. My girl Ginger is going into her 4th heat. The first was 9 months, 2nd 8 months, 3rd 8 and a half months and the 4th--- who knows. This can sometimes be a mystery of sorts, when you are breeding, as I hope to be. Hope this answers your question.