when do female dogs start to go into heat?

[peytons mama]

peyton is 10 months old as of Christmas Eve. She still has not started to show signs (spotting) that she is of the age to go into heat. my vet has told me a broad timeline for it. and well, she went past it. can it be that she is "barren". is there such a thing? as weird as it sounds...i look at everything on her!!! her nipples are growing. as in the little nubs. hehe. i can be so graphic sometimes. not growing like she is gonna start milking soon. she is a rottie and a french mastiff. she is about 75 lbs. she has been about 75 for the last month or so.

[People Whisperer]

They can go in heat as early as 6 months or as late as 24.

[Newly Newfed]

I was asking the same question a few months ago.  Sierra, my Newf, just went into her first heat.  We noticed the spotting last night.  She will be one year old on Jan 24.

[ptkennel]

My newf went into heat at 16 months.  My rotti that we had eons ago went into heat late too.

[peytons mama]

My female dobie went into her first heat at about a year. I think the general rule of thumb is the largest breeds go into heat latest which makes sense as they grow longer and reach sexual maturity later. Maybe your girl is following the mastiff half of her nature for her schedule.
Stela

thanks for that! it does make sense. little dogs quicker growth and smaller parts, big dogs bigger growth and bigger parts!

hehe i find that funny. she follows most of her mastiff half at everything she does. the only thing that resembles her rottie half is she "herds" children in the neighborhood. a little girl decided to go see peyton while she was hanging out outside. peyton must have known she wasn't supposed to so she decided to do circles around her and bark with a sharp (we call it her little girl back) very high pitched bark to get someones attention. i came running outside to see peyton and this little girl playing "ring a round the rosey and jump rope" at the same time. (that's what the little girl said she was doing) we have peyton on a tie out until we can build a fence. but when peyt saw me, she sat on the little girl as if "look what i got mom!" which looking up later i read was a mastiff trait - to sit on something they like or are in "charge" of.

[ZooCrew]

It really depends on the dog, as well as the breed.  My rat terrier Posey was waaaaaaay late as to when we expected her to start.  She didn't go into heat until she was 13 mo old, and then of course she had a false pregnancy afterwards.

I am waiting for her heat cycle to start as we "speak". I was expecting it around Christmas/New Years but she's again a bit off and doesn't look like she'll start anytime soon.