Unlike humans, female dogs (bitches) do not have a monthly menstrual cycle — they cycle through four estrous stages just once or twice a year, with the interval strongly tied to breed size. This simulation renders that cycle as a glowing ring "timeline": a walking dog marker sweeps around the track while three ribbon graphs (estrogen, LH, and progesterone) rise and fall in height to trace hormone levels for every day of the cycle.
The fertile window is not the same as "standing heat." A bitch can stand for mating for days before or after her actual fertile window because sperm can survive in the reproductive tract for up to a week — which is why veterinarians use progesterone blood tests, not just behaviour, to time breeding precisely.
Hormone curves and timings are simplified for illustration and do not replace veterinary reproductive testing.
A glowing ring timeline traces a female dog's estrous cycle stage by stage, with three hormone ribbon graphs — estrogen, the LH surge, and progesterone — rising and falling in height as a dog marker walks the track, while a bright band highlights the fertile window.
How estrogen, LH, and progesterone rise and fall across proestrus, estrus, diestrus, and anestrus, and why the true fertile window sits just after the LH-triggered ovulation rather than at the start of visible heat.
Scrub the cycle-day slider or press play to watch the dog and hormone levels move together. Switch breed size to see how the interval between heats stretches from small to giant breeds.
Because sperm can survive in the reproductive tract for up to a week, a dog can be bred several days before her fertile window opens and still conceive — which is why timing by hormone tests beats timing by behaviour alone.