Oestrous Cycle and Progesterone Testing in Dogs

A female dog will reach sexual maturity at around 6-24 months. Smaller dogs generally experience their first heat earlier than larger dogs. At this stage, the bitch will experience her first heat, or oestrous cycle. Most dogs will then continue to have a heat every 5-11 months, with some breed exceptions.

The female reproductive cycle involves 4 stages:

  • Proestrus – This stage lasts for approx. 6-11 days, with an average of 9 days. During this stage bitches will attract males but will be unwilling to breed. They will typically have a bloody vaginal discharge. Their progesterone levels will be low.
  • Oestrus - This is the stage where the bitch will allow the male to mount and breed with her. This stage will typically last from 5-9 days. During this time the bitch will actively seek males, and the vaginal discharge will change colour from bloody to a light straw colour. Progesterone levels within the blood can be tested and will be seen to increase during this time. Bitches do not ovulate all at once but will continue to ovulate over a 12-96 hour window.
  • Dioestrus – This is the stage following oestrus and begins with cessation of the bitch allowing mating by the male. 56-58 days in pregnancy, and between 60-100 days in non-pregnant bitches
  • Anoestrus – This is the stage of the reproductive cycle where the uterus involutes. In a pregnant bitch, this stage begins with whelping, but in a non-pregnant bitch it is not noticeable. We can monitor this in a pregnant bitch through the use of progesterone testing.

Hormone Testing

Understanding the hormone cycle of a bitch is crucial for understanding the ideal timing of mating in breeding bitches. The hormones which allow for timing of ovulation, and determination of the fertile window include Progesterone and Lutenising Hormone.

Progesterone is a hormone secreted by the ovaries that plays a vital role in regulating the reproductive cycle. During the heat cycle, progesterone levels gradually increase initially, then rapidly rise during ovulation, before plateauing. Elevated progesterone levels support pregnancy by preparing the uterus for implantation and maintaining pregnancy if fertilisation occurs.

Luteinising hormone (LH) is essential for triggering ovulation. A surge in LH levels occurs approximately 48 hours before ovulation. This surge in LH marks the change from proestrus to oestrous, and is a critical indicator of the optimal time for mating to achieve successful fertilisation. Luteinising hormone is not routinely tested as the surge may only occur for 12-24 hours. This means that very frequent blood testing is required, and a larger number of expensive tests need to be performed. The LH surge can instead be predicted from progesterone levels.

Ovulation and the Fertile Period

Ovulation is the process whereby mature oocytes (eggs) are released from the ovaries into the reproductive tract, making them available for fertilisation by sperm. The fertile period, also known as the "breeding window," is the time frame during which a bitch has the highest likelihood of conception. Oocytes require 2 days to mature after ovulation before they are ready to be fertilised.  Therefore, the fertile window is approximately 2-3 days after ovulation. Sperm can live in the reproductive tract for extended periods (7-10 days for fresh sperm) so a mating prior to this fertile window will still allow for pregnancy.

 Timing of Mating Using Progesterone Testing

At McLaren Vale Veterinary Surgery we offer in-house Progesterone testing. This means we can provide highly accurate results within 1 hour.

Progesterone testing is routinely performed on breeding dogs to determine the ideal time for mating to ensure the greatest litter size. Progesterone testing should be performed from approximately day 5 of heat. This may vary in some dogs who have a history of short or long cycles. The progesterone level should be tested at the same time each day. We recommend a blood test performed in the morning, and the bitch to be fasted during the morning prior to testing. Blood tests are then generally performed every 2 days until ovulation is confirmed.

The following is a guide to the important timeline of a cycle and what the different levels of progesterone signify:

  • 6-9nmol/L (~2-3ng/mL): correlates with Leutenising Hormone (LH) peak
  • 16-38 nmol/L (5-12ng/mL): Correlates with Ovulation
  • >38nmol/L: Post-ovulation

It is very important to note that no single value correlates with optimal breeding day ie there is no ideal number at which we should breed. What is important is timing the type of mating to the fertile period.

The ideal time to breed your dog following ovulation will vary greatly depending on the method of insemination being performed (natural or artificial), the number of matings to occur, and the quality of sperm being used in the insemination. These factors will need to be discussed with your Veterinarian to determine the optimal time or times to mate your bitch.

For further advice on progesterone results and the optimal breeding time, please call us at McLaren Vale Veterinary Surgery to book an appointment on 8323 8522.