Puberty of the female
The average age for a female dog to reach puberty, considering it is at the beginning of the proestrus, commonly know as being in heat, is between 9- 10 months old. This normally increases between 6 to 24 months.
When this moment comes, we will notice that the genital organs of the female dog are swollen and bleeding begins. When it is a small race, we probably won't notice any bleeding since the dog usually cleans itself. This bleeding lasts for 9 days, varying from 3 to 17 days.
This part of the cycle is called proestrus. It ends the moment the female dog allows copulation. There are some hormonal and functional changes in their reproductive organs which represent the fertility in female dogs. This stage is called oestrus. While it is bleeding, it doesn't allow copulation and it is not fertile. The Oestrus lasts for 9 days, varying from 3 to 21 days.
They will spend an average of 6 to 7 months until they reach the proestrus state again; this first interval can be more irregular than the future ones. TO be able to tell what is normal with our female dog, we need to jot down every change. This also allows us to notice if something is not quite right.
In this picture, you can se the edema complication in the genital area of a Yorkshire puppy the first time its in heat.