Dog Heat Cycle & Ovulation Predictor

Understanding the Dog Heat Cycle (Estrous Cycle)

The heat cycle, or estrous cycle, is the reproductive period in an unspayed female dog. Unlike human cycles, the dog's cycle typically occurs only once or twice a year. The cycle has four distinct phases, which are essential to track for breeding purposes or for managing the dog's health.

The Four Phases of the Heat Cycle

Tracking the start date of the last heat is crucial because the subsequent cycle phases occur predictably relative to that first day. The entire cycle, from start to start, typically lasts 6-8 months, but can vary widely (4 to 12 months) by breed and individual.

1. Proestrus: This is the first phase, marked by swelling of the vulva and bloody discharge. The dog is attractive to males but usually refuses to breed.

   \(\text{Duration}: 7-10 \text{ days}\)

2. Estrus (Fertile Window): This is the period of true fertility and ovulation. The discharge becomes lighter or yellowish, and the female dog becomes receptive to mating.

   \(\text{Duration}: 7-10 \text{ days}\)

3. Diestrus: This phase follows estrus and lasts approximately two months. Whether the dog is pregnant or not, the progesterone hormone remains high. This is the period of gestation if breeding occurred.
4. Anestrus: This is the inactive phase, lasting several months, where the reproductive organs are resting before the cycle begins again.

Predicting the Fertile Window and Ovulation

The calculator estimates the Peak Fertile Window based on average timing, which is typically Day 9 to Day 14 from the start of the proestrus phase. However, ovulation timing is highly individual. For precise breeding, veterinarians recommend progesterone testing, which measures the progesterone level in the blood to pinpoint the exact time of ovulation.

The most fertile period for breeding is generally considered to be 2-4 days after ovulation occurs.

Whelping Date (Gestation Period)

If the date of breeding is known, the Estimated Whelping (Due) Date is calculated by adding the average canine gestation period to the breeding date. The standard gestation period for dogs is:

\(\text{Whelping Date} = \text{Date of Breeding} + 63 \text{ days}\)

Whelping can occur anytime between 58 and 68 days from the first breeding. If the breeding date is unknown, the calculator cannot provide a reliable due date.