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How to tell if your dog is in heat
Understand the basic reproductive cycle of your dog.
When wondering if your dog is in heat, it first helps to understand her normal hormonal cycle. When a female dog reaches maturity, and is physically ready to reproduce, her estrogen levels increase, initiating the release of eggs from her ovaries.
If mating occurs during this period, the eggs can then be fertilized and an embryo can be produced. Female dogs, will generally go into heat during puberty, at around 6 to 24 months of age depending on breed.