Often bitches are referred to me when they fail to conceive. Their owners are frustrated and abjectly disappointed, but resolutely determined to find out why no puppies are forthcoming. They are often prepared to go to any length to get to the cause, including chromosome analysis and surgical biopsy. Most of the time these tests are not necessary. In my practice, over half of the females presented for work-up of an infertility problem are perfectly normal reproductively. So if these bitches are perfectly normal, why aren’t they pregnant? They aren’t pregnant because their breedings were improperly timed.
The average bitch ovulates about 12 days after the onset of proestrus. The most prominent signs of proestrus onset are vulvar swelling and bloody vulvar discharge. A common rule of thumb is to breed bitches on day 11 and 13 after onset of proestrus. The vast majority of bitches will conceive an average-numbered litter of puppies when bred on these days (to a fertile male). However, some bitches ovulate as early as 3 days or as late as 26 days after proestrus onset. Even taking into account that canine spermatozoa can live in a normal female reproductive tract for at least 5 days, breedings that occur on days 11 and 13 for these early and late ovulators will not result in conception. Remember that while sperm cells are relatively long-lived, oocytes (eggs) remain viable only about 24 hours after they are ready to be fertilized.
Success in breeding early and late ovulating bitches demands that breedings be properly timed, which in turn, demands that the time of ovulation be accurately determined. Early and late ovulating bitches were used as examples to illustrate the importance of accurately timed breedings. There are other breeding situations when ovulation timing should be performed:
When the breeding is being done by AI (artificial insemination).
When bitches experience a “silent estrus” and fail to show standing
When bitches are to be shipped. It is best to ship bitches after their LH surge to avoid a decrease in LH that might result from the stress of shipment.
When the dog is heavily “booked” so as to avoid sperm cell depletion by over-usage.
When there is a need to accurately predict whelping dates, as in cases of planned
Caesarean sections, or cases of previous dystocia (difficult birth), or with any valuable litter. One of the most gut-wrenching decisions a veterinarian has to make is the decision to surgically deliver puppies when no breeding dates or only breeding dates, and not ovulation dates, are known.
Ovulation dates are determined by measuring serum concentrations of progesterone during late proestrus and estrus. Progesterone levels in the bitch begin to rise about 2 days before ovulation. Serum progesterone is <1.0 ng/ml when bitches are not “in heat” and during most of proestrus. Values increase rapidly to >1.0 ng/ml about 2 days before ovulation. Serum progesterone is 4-10 ng/ml when bitches are ovulating. This 2 day interval between the initial rise in progesterone and ovulation represents the first “2” in our equation, “2 + 2 + 2 = 10 or more.”
But our task is not done just because we know when ovulation is taking place. That’s because the bitch has yet another reproductive idiosyncrasy. Unlike other domestic species, which ovulate ova (eggs) as secondary oocytes that are ready for immediate fertilization, the bitch releases ova in a more immature state as primary oocytes. It takes about 48 hours (or 2 days) for these primary oocytes to mature into secondary oocytes and become ready to accept spermatozoa in the fertilization process. This 2 days for oocyte maturation is represents the second “2” in our equation, “2 + 2 + 2 = 10 or more.”
When ovulation does occur, the ova are not all released in an instant of time. It typically takes about 48 hours for all of the ova to be released from the ovary. That’s the rationale for the common practice of breeding dogs twice 2 days apart. This 48 hour or 2 day duration of ovulation, represents the third "2" in our equation "2 + 2 + 2 =10 or more."
It should be pointed out that serum progesterone concentration measurement is only one tool used for predicting both the time of ovulation and optimal breeding dates. It is prudent to use all available methods for planning a breeding. Other diagnostic tools include vaginal cytology, vaginoscopy, and LH (luteinizing hormone) assays.
Proper timing of ovulation, along with knowledge of canine reproductive physiology and endocrinology, are necessary in managing a successful breeding program. Use progesterone assays to predict when ovulation will occur, understand that canine ova are not ready to be fertilized at the time of ovulation, and do 2 breedings to ensure that rigorous spermatozoa are “ready, willing and able” at the instant each ovum matures to a fertilizable state. That is the way to make “2 + 2 + 2 = 10 or more. . . PUPPIES!”
Jane Barber, DVM, MS, Diplomate ACT
Dr. Barber is board certified in Theriogenology and is a member of the American College of Theriogenologists. She is also certified to perform PennHIP radiographs for evaluation of hip joint laxity. Prior to her graduate training in reproduction, Dr. Barber completed a clinical residency and Master’s degree program in veterinary behavior. She provides behavioral consultation and behavioral modification therapy for pets. Her veterinary practice, Veterinary Specialties at the Lake, is located north of Charlotte in the Lake Norman area.
Jane Barber, DVM, MS, Diplomate ACT