Understanding the Canine Estrus Cycle

Using progesterone testing to time the optimal breeding day in canines is a common practice among breeders and veterinarians. The rise and fall of progesterone levels in a female dog's blood provide crucial information about her reproductive cycle, particularly regarding ovulation and the most fertile period. Here's a breakdown of the process:

1. Understanding the Canine Estrus Cycle: Female dogs typically come into heat (estrus) once or twice a

year. The estrus cycle has several stages:

• Proestrus: This is the beginning of the heat cycle. The female attracts males but is not yet receptive to breeding. This stage lasts about 9 days but can vary.

• Estrus: This is when the female is receptive to the male. Ovulation occurs during this stage, which lasts about 9 days but can vary significantly between dogs.

• Diestrus: The post-estrus stage.

• Anestrus: The period of reproductive inactivity between estrus cycles.

2. Starting Progesterone Testing: It's generally recommended to start testing a few days after the onset of

proestrus, which is characterized by vulvar swelling and bloody vaginal discharge. Testing too early might miss

the initial rise in progesterone.

3. Rise in Progesterone and Ovulation: Progesterone begins to rise just before ovulation. A significant

increase in progesterone levels, usually around 5 ng/mL, indicates that ovulation is imminent. However, the

optimal time for breeding is typically 2-3 days after ovulation, as it takes time for the eggs to mature and be ready

for fertilization.

4. Determining the Best Breeding Day: Once progesterone levels reach 5 ng/mL, ovulation usually occurs

within the next 24-48 hours. Considering the time required for egg maturation, the best days for breeding or

insemination are generally when progesterone levels are between 10-20 ng/mL. This usually corresponds to 2-3

days post-ovulation.

5. Frequency of Testing: The frequency of testing can vary depending on the veterinarian or breeder's

preference. Initially, testing might be done every other day, but as the levels approach the expected rise, daily

testing might be done to pinpoint ovulation accurately.

6. Benefits:

• Precision: Progesterone testing offers a scientific and precise approach compared to just observing physical and behavioral signs.

• Higher Conception Rates: Timing based on progesterone testing generally results in higher conception rates.

• Useful for Artificial Insemination: For breeders using artificial insemination, especially with chilled or frozen semen that has a limited viable lifespan, precise timing is crucial.