Winter 2010

Since 1967, Royal Canin has been at the forefront of developing innovative nutritional responses in the field of dog breeding. Even if nutrition is fundamental in breeding, it cannot give all the keys for success. Application of reproduction techniques is the deciding factor.

Breeder's Handbook
The Canine Reproductive Cycle: A Complex Biological Process

Beginning with proestrus and ending with anestrus, the canine reproductive cycle is a complex biological orchestration of events which must progress in a precise manner to have a successful outcome: healthy puppies. Ovulation, or release of eggs from the ovary, is one of the most important events in the reproductive cycle. It occurs during the second phase of the estrous cycle and can be monitored by blood tests or vaginal cytology. Although this knowledge can give the breeder the most accurate time frame for successful mating, there are still many variables that determine whether puppies will be born.

Fertilization and Implantation

Once ovulation occurs, the eggs will require 48 hours to mature before they are ready to be fertilized. During this time they remain in the upper portion of the oviduct, or fallopian tube. Gestation begins with the fertilization of an egg, or ovum, by a single sperm cell, or spermatozoon. Once this union occurs, cell division begins and continues at a constant rate. Migration of the developing embryos through the oviducts and into the uterus takes approximately one week. Once they have reached the uterus, they will float in a nourishing fluid secreted by the lining of the uterus for another 14 to 21 days before they implant into the uterine wall. It is vital that the tissues and environment in the oviducts and uterus remain healthy and free from any infection and/or inflammation that could kill either the eggs, sperm, or the developing embryos. When the embryos attach to the uterine wall, this is referred to as implantation, or nidation. Once this is accomplished, cell division continues and further development occurs rapidly. 

The placenta has many functions— nutritive, protective as well as hormonal.

After nidation, the fetal and maternal placentas begin to form. In dogs, the blood supplies of the mother and the embryos (and later, the fetuses) do not comingle as they do in humans. They are, however, in close proximity so that nutrients and oxygen can pass from the mother to the baby, and waste from the baby to the mother can be exchanged. In the dog, the placenta forms a complete band of tissue around the developing puppy. This type of placenta is classified as zonary. It secretes a hormone called Relaxin, which is only present during pregnancy. Therefore, its presence in the blood of the female can be used to definitively diagnose pregnancy before ultrasound or radiology is practical.

Pregnancy and Progesterone
The maintenance of pregnancy is mainly controlled by a hormone called progesterone. In the dog, it is secreted by structures in the ovaries called corpora lutea, or yellow bodies. They are composed of the cells of the follicles that nourished the eggs before ovulation. Progesterone continues to be secreted from the ovaries for approximately two months, regardless of whether the female became pregnant. This can lead to the development of pseudopregnancy, or false pregnancy. The female progresses as though she were actually pregnant. She will assume behaviors associated with imminent whelping, i.e., nesting. She may even develop mammary tissue and make milk. She will usually adopt an inanimate object such as a stuffed toy to nurture. On the contrary, if she actually did become pregnant and the progesterone level drops sharply, the pregnancy will most likely be lost.

Progesterone is the main hormone in gestation. The hormone Relaxin can be used to diagnose pregnancy.

The Two Distinct Stages of Gestation


Cell Division
Gestation begins from the moment that a spermatozoon penetrates the ovum, after which the first cell divisions begin.

During gestation there are two distinct stages that are hallmarked by the rate of development of the future puppies, and the energy needs of the mother. The first is embryogenesis and it consists of the first six weeks of pregnancy. At this time the mother’s energy needs do not change significantly. During this stage all the puppy’s organ systems are being developed. Cell division and DNA replication are taking place at a phenomenal rate. Eyelids appear at 32 days and the palate closes at 33 days. Individual toes can be seen at 35 days. In addition, the neural, musculoskeletal, cardiovascular, respiratory, lymphatic, digestive, integumentary, and urogenital systems are forming. These events must take place in precise and harmonious progressions to ensure viable, fully developed puppies free from birth defects. If any disruption occurs during this development, results may be catastrophic. For example, if the palate does not fuse at just the right time it will not happen later in gestation. The consequence of this interruption of normal formation is cleft palate. At the end of embryogenesis the future puppies are still very small in comparison with their final birth rate.

The second stage of gestation is correlated with the embryos becoming fetuses. It occurs at the beginning of the last three weeks of pregnancy and continues until birth. During this stage the fetuses will gain 75 percent of their birth weight! Subsequently, the mother’s energy needs escalate accordingly. Even though development of some organ systems will continue after birth, the fetus is mature enough to survive outside the uterus as a neonate after just 60 to 63 days in the womb!

Breeders can support the gestation process, beginning with the estrous cycle, by ensuring their males and females have received proper veterinary care, including appropriate vaccinations, heartworm prevention, and treatment for internal and external parasites. Providing optimal nutrition is vital in all stages of the reproductive cycle. This includes not only gestation and lactation in the female, but also the time between breedings when her body is healing from the previous pregnancy, birth, nursing, and weaning.

Proper care and nutrition during this period is crucial, as is the nutrition supplied during the estrous cycle itself. Attention to these factors will optimize a successful pregnancy and subsequent delivery of a healthy litter of puppies. —Melinda Fleming, DVM

©Royal Canin USA, 2011

Ronald N. Rella, Director, Breeder Services
Customer Service | Phone: 919-233-9767 | Email:

© The American Kennel Club 2010