Reproductive veterinary specialist explains the bitch's estrus cycle (heat), how to achieve a successful natural mating and avoid (AI) artificial insemination.
CANINE ESTROUS CYCLE
Joni L. Freshman, DVM
Successful breeding management can be provided by breeding every 2 to 3 days during cytologic estrous. Another option is ovulation timing with a progesterone assay and breeding 2 and 4 or 3 and 5 days after ovulation.
Because canine spermatozoa survive up to 7 days in the bitch’s tract, and ova are fertile for only 12 to 24 hours, it is better to breed too early than too late.
Without an understanding of reproductive physiology reading a technically challenging paragraph like that can leave people asking themselves one question, “What”? The goal of this article is to provide a basic outline of the canine estrous cycle. I’m going to keep this discussion quick and simple. Just remember, we need to understand this information in order to learn how vaginal cytology allows us to build a fertility timeline.
To understand the basic physiology of the canine estrous cycle it is necessary to learn about the four different stages of the cycle. The four stages include proestrus, estrus, diestrus (A.K.A. metestrus) and anestrus. All of the veterinary journal articles I reviewed agreed that while there is an average duration for each stage of the estrous cycle, each bitch is unique. That is why making management decisions based on general breeding guidelines can be a recipe for failure.
PROESTRUS: This is the period of time between the first observed bloody discharge until the bitch will stand for the stud. Swelling of the vulva will be seen. Males will be attracted, but the bitch will not be willing to breed. The average duration of proestrus is 9 days. However, the majority of the articles I reviewed agreed that proestrus might be as short as 3 days or as long as 17 days. In one article the range went out to 27 days. During proestrus luteinizing hormone (LH) levels remain near baseline. There is a slight increase in progesterone levels towards the end of proestrus. Estrogen levels continue to rise until they reach their peak 1 to 2 days prior to the end of proestrus. The role of these hormones will be explained in an upcoming article on vaginal cytology.
ESTRUS: This is the period of sexual receptivity. The bitch will flag her tail and stand for the stud. The average duration of estrus is 9 days with a range of from 3 to 21 days. Estrus begins due to falling levels of estrogen and rising levels of progesterone. It is also believed that the changing levels of estrogen and progesterone signal the preovulatory surge of LH. LH causes the follicles that have formed on the ovaries to ovulate. Ovulation occurs between 24 to 72 hours after LH reaches its maximum concentration. Following ovulation the ova require up to another 3 days of develop before they can be fertilized. After that they survive for approximately 1 day.
DIESTRUS: This stage of the cycle begins on the first day, following estrus, that the bitch refuses a male.
Progesterone levels continue to rise until approximately the 15th day of diestrus.
After achieving peak levels there is a steady decline in progesterone concentration, which lasts for 5 to 6 weeks. During this period progesterone levels will be very similar in both pregnant and non-pregnant bitches. These elevated levels in non-pregnant bitches are responsible for pseudopregnancies.
ANESTRUS: No obvious reproductive activity or behavior is seen. This period lasts until bloody discharge signals the onset of proestrus.