Why do we need to know when a bitch ovulates?
There are two main reasons to indentify the day of ovulation: to accurately determine the date(s) for breeding, and to predict a whelping date.
Precise breeding dates are necessary when using artificial insemination techniques, especially with fresh-chilled or frozen semen. Knowing exactly when to breed can save time and expense, ie: when the bitch or sire must travel for the breeding. Fresh-chilled semen lasts 48-72 hours once warmed, and frozen semen lasts less than 12 hours once thawed. If these semen samples are used too early, the sperm will be dead before the eggs are ready to be fertilized.
Bitches have a unique estrous cycle. Vaginal bleeding and swelling starts with a proestrus period, which may last 3-21 days, and continues with an estrous period which may also last 3-21 days. Somewhere in the estrous portion of the cycle lies a fertile period which lasts only about 48 hours. An initial rise in progesterone levels coincides with a decrease in estrogen, and a peak of LH (luteinizing hormone) to trigger ovulation about 48 hours after the initial rise. We have seen ovulation as early as day 6 and as late as day 25. This progesterone-related event can be completely unrelated to estrogen-influenced signs: vaginal swelling, type of discharge, changes on vaginal smears, and tendency to stand for breeding! The eggs are mature for fertilization about 48 hours after ovulation.
We use three methods to track the cycle in our effort to catch the day of ovulation while conserving cost: vaginal smears, progesterone levels, and vaginoscopy. We may run a baseline progesterone initially, but then we wait until 70% cornification on the vaginal smear indicates that the progesterone may start rising. We track progesterone levels every 1-3 days depending on the type of semen to be used and the point in the cycle. We use vaginoscopy to fine-tune ovulation timing in some cases, looking at the vaginal folds with an endoscope to watch for flattening or “crenation.” Crenation starts with ovulation and maximizes just before the WBC flush (end of fertile period).
We can use the ovulation date, together with the date of initial rise in progesterone and the shape of the individual progesterone ‘curve,’ to determine the best days to breed.
We can also predict that the whelping date will be 63 days +/- 1 day from the ovulation date. Remember that the day of ovulation varies so much that apparent gestation based on breeding dates may be 57-69 days!
Knowing your bitch’s whelping date is valuable even for routine pregnancies. If your bitch needs a planned c-section or is at risk of needing a c-section, knowing the predicted whelp date helps us to ensure that the puppies are mature, but not left in the uterus so long that the placentas start to degrade. Singleton litters (or those with 2-3 pups) may not trigger labor to begin at all, and we may be left watching for signs of fetal distress. Ovulation timing allows us to predict the day on which we should intervene. This allows us to save puppies’ lives in cases where bitches never enter first-stage labor or do not have a temperature drop.