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 is the exact ovulation date which is important if you are trying to select the sex of the pups-to-be. (See the page on the basics of how to select the sex of the puppies).
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. Vaginal cytology can also provide some general information. 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 (caesarean) 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.
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
The progesterone test 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.
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.
Figure 2. Predicting Breeding Time And Whelping
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.
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 egg also needs time to mature after it is ovulated, generally 48 hours from ovulation until it can be fertilized. Fertilization occurs in the oviduct (Fallopian tubes) regardless of the method of insemination. The fertilized egg then travels into the uterus but does not implant until 17-18 days after ovulation. If there are problems with the lining of the uterus, the egg 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 resorbed.
Progesterone levels during pregnancy and whelping
After ovulation, progesterone concentrations continue to increase for 2-3 weeks, finally reaching 10-80 ng/ml. This level is necessary to maintain a pregnancy. In the dog, the progesterone level will remain at this level 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 time of whelping or the eproper 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.
The following chart indicates the estrus cycle (by days), the hormone levels, breeding times, and whelping dates.
Day Estrogen Level Progesterone Level Luteinizing Hormone When To Breed Whelping Indicators
(LH) Level Based On Semen type
-3 day high < 1 ng/ml low -
-2 moderate 2-3 ng/ml surge -
-1 low 3-4 ng/ml low -
low 5 ng/ml low -
+1 day - > 5 ng/ml - natural semen
+2 day - > 5 ng/ml - fresh chilled semen
+3 day - > 5 ng/ml - frozen semen
- 10-80 ng/ml - -
-
2 ng/ml - - temperature drops
-
- 1 ng/ml - - whelping
-
Breeding: page -5
Ovulation
day
+2 to +3
weeks
+62 days
+
1
+63 days
+
_
_
1
Puppies, both male and female, are born with their reproductive organs present but not fully developed. The ovaries of the female puppy do not become fully developed until the puppy matures, usually after six months of age. At birth in the male, the testicles are not usually fully descended within the scrotal sac. They are generally positioned inside the abdominal cavity or located within muscles in the abdominal wall.
Female reproductive anatomy
The reproductive system of dogs and humans are very similar. In the female, the reproductive system is composed of the ovaries, oviducts, uterus, cervix, and vagina. The ovaries are the site of production of the unfertilized eggs, and many of the hormones responsible for heat cycles and the maintenance of pregnancy. The eggs pass from the ovaries into the oviducts. These small finger-like tubes are the site of fertilization by the sperm. From there the eggs pass into the uterus, which is composed of the left and right horn and uterine body. The developing embryos mature within the uterus, attached to its walls by the placenta which also surrounds them.
Heat cycles
The heat cycles of the female (bitch) are caused and controlled by hormones that are produced and released by the ovaries and other glandular structures within the body. The ovaries are paired structures that become increasingly active when the animal passes through puberty, at the first heat cycle. This ranges from between five and eighteen months of age depending on the individual and the size of the animal. In the toy and small breeds, heat cycles occur as early as five months of age, while in the giant breeds, this may not occur until the animal is fourteen to eighteen months old. Typically, these cycles will occur every six to nine months throughout the life of the animal. In the very young and very old, there may be 'silent heats' with no outward signs that are detectable by the owner or sometimes even other dogs. Dogs do not undergo any form of menopause. There have been rare cases of heat cycles resulting in pregnancies at fifteen years of age.
The heat or estrus cycle of the female is divided into four different stages. There is great variation in the length of these cycles among individuals of the same breeds and among various different breeds. Additionally, the same animal may have significant variations over the course of a lifetime. It is therefore impossible to talk about the cycling of bitches using exact dates or time periods.
Proestrus: The first stage of a heat cycle is a preparatory period referred to as proestrus. This follows a period in which the reproductive system, was from all outward appearances, inactive. Proestrus typically lasts five to nine days. On the first day of proestrus, the vagina becomes swollen and a bloody discharge is soon observed. During this stage males show an interest in the female, but she will be unreceptive to them.
Estrus: The next stage is referred to as estrus. This is the active breeding phase, and will usually last from five to nine days. Bleeding from the vagina is very slight or completely absent at this point. Eggs are released from the ovary and travel down the oviduct. During estrus males will definitely be attracted to and attempt to mate with the female. The female will allow them to mount her, resulting in intercourse. In the dog, a 'tie' usually occurs in which the male and female are held together physically, with the vagina tightly enclosed around the glans penis. Ejaculation will occur and sperm cells will enter the uterus and make their way to the oviduct, where their union with the egg will result in fertilization. A tie, however, is not necessary for conception to take place. The union of the egg and sperm results in the formation of a fertilized egg, which is referred to as a zygote. This matures further, developing into an embryo and then a fetus.
Diestrus: Following estrus is the diestrus period. This extends from the time when the female dog is no longer receptive to the male to the end of pregnancy. In cycles in which a pregnancy did not occur, diestrus will last for a period of up to 80 days. In early diestrus, the embryos and their placentas attach to the wall of the uterus, from which they will derive their oxygen and nutrients.
Anestrus: Following diestrus is anestrus. This is the quiescent period between heat cycles characterized by no outward physical or behavioral signs of sexuality.
Male reproductive anatomy
In male dogs, there is no seasonal period of increased or decreased sexual activity. Rather, they can be stimulated at any time by nearby females that are in season (heat).
In the male, the important structures of the reproductive system are the testicles, ductus or vas deferens, prostate gland, and penis. Sperm production and storage occurs within the testicles. Upon ejaculation, the sperm is transported to the prostate gland by the vas deferens. Within the prostate, additional fluids are added to the sperm to nourish it and aid in its transport from the penis and through the uterus.
The sperm and prostatic fluids, at the level of the prostate gland, enter the common urethra and are carried from the body through the penis. The penis of the dog has two specialized structures. The glans penis is a bulb-like dilation at the base of the penis, which fills with blood and holds the penis within the vagina during intercourse. Within the penis is a bone that maintains the shape and direction of this organ during mating. The penis is protected from the environment, as it is enclosed within the sheath or prepuce.
The more common disorders of the reproductive tracts of puppies include vaginitis in females, and cryptorchidism and phimosis in males.
Understanding the preceding basics is a must before one should attempt to breed with a specific goal in mind such as using A.I. to choose the sex of the puppies.
Anatomy and Function of the Reproductive System in Dogs
Click here to access www.goudabooks.com
The most recent book addresses sex selection in mammals. How to choose the sex of your baby (or puppy.) It started as a paper on conditioned artificial insemination on mammals back in medical school, before I realized that becoming a GP wasn't my calling, and I switched to pharmaceutical research and analytical chemistry. As you know, for years, on this site, I announced that the next litter will be all males or all females, and a 9 pups litter was 9 males, 8 pups litter, 8 females. I also assisted many couples to select the gender of their baby, and never failed.
The book has a section dedicated to breeding dogs, artificial insemination, sex selection and how to induce the estrus of the female to time pregnancy and whelping avoiding the very hot and the very cold months.
"Choosing the sex of your baby ... made simple, made certain." It is now available at Chapters, Coles and Barnes & Noble book stores. In the absence of shelf-copies at your local bookstore, you can still order it via their in-store database "search&order" PCs.
My books are also available at amazon.com "search by author name: Paul Gouda."
