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Progesterone Levels & Vaginal Cytology

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When it comes to reproduction “timing” is everything to make sure that the sperm and eggs meet on time! We use lots of different indicators and tools besides just animal behavior to determine when is the “best” time. The measurement and charting of hormones is fast becoming one of our most reliable tools. There are multiple hormones that help to regulate the estrus (heat) cycle and pregnancy in dogs. These include:

  • Estrogen: Stimulates the ovaries to produce eggs.
  • Luteinizing Hormone (LH): Stimulates the ovaries to release the eggs.
  • Progesterone: Maintains a pregnancy.

We need to fully understanding how the hormone levels change so they can help us in determining the best time to breed naturally or with artificial insemination or surgical implantation and also when to anticipate whelping or to do an elective C-section.
It seems that usually most mammals ovulate when the estrogen level in the blood is still increasing. Dogs, however, ovulate when the estrogen level is already declining and the progesterone level is increasing. Estrogen levels can give us a general idea of when a dog will come into “standing” heat, but are not sufficient to determine when breeding should actually take place for optimal conception rates.
Vaginal cytology can also provide some general information. Vaginal cytology is performed on female dogs during their estrus cycle to help determine the optimum time to breed and enhance the success of pregnancy. The types of cells present in the vagina vary depending on the stage of estrus. A swab is taken of the cells lining the vagina and analyzed under a microscope. Usually more than one swab is required to determine the optimum time to breed.
Progesterone levels and luteinizing hormone (LH) levels are the best indicators of when ovulation will take place and when is the best time to breed. They are also useful in determining whelping dates, allowing an owner to reserve the appropriate days on the calendar and even to schedule a C-section (Cesarean) weeks in advance.

The progesterone test is not species specific so the test can be run in in clinic, in  human labs or veterinary labs. Results should be available in less than 24 hours to keep things on time. Different labs have different tests and report result in different measurement units. To switch between the American units and the International units multiply by 3.18.

These are the International numbers that we use from our IDEXX laboratory: The normal progesterone ranges are as follows:
Anestrus (not in heat) is less than 3 nmol/L
Late Proestrus (early heat) is 6-8 nmol/L
LH surge is 8-12 nmol/L
Ovulation is 12-24 nmol/L
Past Ovulation is greater than 24 nmol/L

The progesterone test can be done every 2-3 days starting about 3-5 days into the heat. Timing of the test can be more certain if the lengths of the dog’s previous heat cycles are known. The beginning progesterone levels are typically less than 1.0 ng/ml until the day before the LH surge. The day of the LH spike, serum progesterone concentrations are 2-3 ng/ml; the day following the LH surge, the serum progesterone concentration is 3-4 ng/ml. Ovulation occurs at a progesterone level of 5 ng/ml.

Timing of breeding

The aim is to identify when the progesterone level reaches 2.5 ng/ml so the mating schedule can be set up, or the veterinarian and owner of the male dog can be notified that they should be prepared to collect and ship a semen sample. Depending upon the type of semen used, optimal times for natural or artificial insemination are:

  • Natural breeding should occur 3 days after the 2.5 ng/ml mark. Sperm in fresh semen survive 5-7 days after insemination.
  • Artificial insemination using fresh chilled semen should be used for a 1-time breeding. Insemination should take place 4 days after the progesterone reaches the 2.5 ng/ml mark or 48 hours after the 5 ng/ml mark. Sperm in chilled semen survive 48-72 hours after insemination. With artificial insemination, the semen should be deposited into the cervix to increase the chance of it being drawn into the uterus.
  • Artificial insemination using frozen semen should be performed 5 days following the 2.5 ng/ml mark or 72 hours after the 5 ng/ml mark. Sperm in frozen semen survives less than 24 hours after insemination. Frozen semen is ideally deposited directly into the uterus through surgery to increase the chance of pregnancy.

We also advise additional tests be performed on your breeding female prior to her estrus cycle. Blood work including a thyroid analysis will rule out any potential breeding problems that may be addressed prior to the breeding period. Please call and set up an appointment with one of our veterinarians to discuss your breeding program in greater detail.