We have a Cairn Terrier and wondered if anyone knew when we could expect her first season and how often for this breed.  I am used to larger dogs who normally start around a year but for some reason I think smaller dogs would be earlier.  She is now over 10 months old.

I don't know the answer to your question, but I'd like to be cheeky and tag a similar one on to your post :-D

When can I expect my 15 months Sheltie to have her first, I think she may have had a start of one when my 13 months Sheltie had hers at a year, but after a week it all stopped and nothing since.

To be honest i don't think there is a set time for any breed. Its individual like with women. My medium sized bitches were around 15-18 months whereas i have known some of the same breed come in at 6 months. I would imagine you would find it could be any time after 6 months, and with smaller dogs they are likely to be earlier than it would be for a larger dog as they mature quicker.