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.