The Canine Heat Cycle (The Estrous Cycle)
- Active heat cycles last 18-21 days, however, exact time frames are difficult to give as they vary greatly depending on the dog, its breed, and its environment.
- Stage 1: Proestrus
- Vulva swells
- Bloody discharge
- Lasts about 7 to 12 days
- May attract males but not time for breeding
- Stage 2: Estrus
- Discharge color lightens to pink
- Vulva enlarged and soft
- Lasts between 3-11 days
- May be receptive to males past the window of fertility. To ensure optimum time for breeding vaginal smears or blood tests measuring female progesterone levels can be conducted during heat.
- Stage 3: Diestrus
- Around day 14
- The discharge becomes darker red again, decreases in volume
- Vulva returns to normal
- No longer accepting mates
- Lasts 60-90 days with no pregnancy
- Lasts until birth if there is pregnancy
- Stage 4: Anestrus
- The time frame between the end of the cycle and the beginning of the next
- Many dogs experience irregular heat cycles, especially young dogs. Around age two most dogs begin to develop regular heat cycles, yet they still may experience irregularities. There are certain aspects that can alter canine heat cycles including the individual dog, a dog’s breed, and even its environment.
- An individual dog may experience irregular cycles for a variety of reasons. Dogs who suffer from certain medical conditions, disorders, or genetic abnormalities are more at risk for irregular heat cycles. Certain medications may also influence cycles.
- Types of breeds also play an important role in dogs’ heat cycles. Heat cycles vary between breeds with some small dogs experiencing 3 cycles per year and some large breeds only experiencing 1 cycle per year. Some dogs’ cycles, like Basenjis and Tibetan Mastiffs, even line up with certain seasons.
- A dog’s surroundings can also influence their cycles. An example of this is when multiple female dogs share the same environment, it is possible for their heat cycles to sync. Environmental influence can also be seen in the way that improper care can result in irregular and skipped heat cycles. If dogs are not receiving proper food, nutrients, exercise, and care their bodies aren’t able to function optimally and they can’t properly carry out heat cycles.
