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.
Understanding how the hormone levels change can help in determining the best time to breed and when to anticipate whelping. Most mammals ovulate when the estrogen level in the blood is increasing. Dogs, however, ovulate when the estrogen level is declining and the progesterone level is increasing. Estrogen levels can give us a general idea of when a dog will come into heat, but are not sufficient to determine when breeding should actually take place. 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 the whelp date, allowing an owner to reserve the appropriate days on the calendar and even to schedule a c-section (cesarean) weeks in advance.
Luteinizing hormone levels. LH is species-specific, meaning it is chemically different in different species. Blood testing for LH, therefore, needs to be done at a veterinary lab or at a veterinary clinic where access to the specific test for that species is available. Test results are generally available within less than 24 hours of submitting the sample. LH tests are quite expensive and must be done daily so utilizing this test is not a common practice. The LH test needs to be done daily starting toward the end of proestrus. The LH spike typically lasts only 24 hours or less, so the test needs to be done every 24 hours in order to catch it. If the testing starts too late, the spike will be missed. The spike generally occurs 48 hours prior to ovulation. Figure 1. Hormone Levels During Estrus and Pregnancy
Progesterone levels and breeding. Progesterone is not species specific so the test can be run in human labs or veterinary labs, results should be available in less than 24 hours. **** With our Progesterone Analyser you can now do this test in your own home in less than 60 minutes!
The progesterone test can be done every 2-3 days starting about 3-5 days into the heat cycle. 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 at least 5 ng/ml. Our goal is to test the bitch until she surpasses the 5ng/ml to be sure she has not stalled or is splitting her cycle, it is critical to keep testing until she has reached 10ng/ml or more.
Figure 2. Predicting Breeding Time And Whelping
Timing of breeding. The aim is to identify when the progesterone level reaches 5-10 ng/ml or more 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 listed on our chart below.
Fertilization and implantation. The sperm require a period of approximately 7 hours after ejaculation before they are capable of fertilizing an egg. This period is referred to as the "capacitation time." The eggs also need time to mature after ovulation, generally 48 hours from ovulation until they can be fertilized. Fertilization occurs in the oviduct (Fallopian tubes) regardless of the method of insemination. The fertilized eggs then travel into the uterus but do not implant until 17-18 days after ovulation. If there are problems with the lining of the uterus, the eggs may not implant or the placenta may not grow or be maintained. A normal placenta grows into the lining of the uterus. If implantation does not occur or the placenta does not grow normally, the fetuses are adsorbed.
Progesterone levels during pregnancy and whelping. After ovulation, progesterone concentrations continue to increase for 2-3 weeks reaching as much as 80 ng/ml, this level is necessary to maintain the pregnancy. In the dog, the progesterone level will remain high for about 60 days whether or not the dog is bred, and whether or not she is pregnant. About 48 hours before whelping, the progesterone level drops to the 2 ng/ml range and within about 24 hours of whelping, the level drops to the 1 ng/ml range. This can help determine the proper timing of a c-section, especially if the progesterone level or LH level were not used to determine the ovulation date. By correctly determining the whelping time, it can prevent puppies from being taken by c-section too early and thereby decreasing their chance of survival. Figure 3. The following chart indicates the hormone levels and breeding schedule that we follow. Please understand this chart is to be used with our test equipment only, it may not be accurate with other test equipment or other methods.