Timing the Insemination

Timing the breeding of a bitch is a the most important part of performing an AI mating. My belief is that many times a failed AI is due to improper timing of mating and that the bitch has a "normal" estrus cycle that may be simply timed a little different then the average ovulation time of 8 to 12 days. The biggest problem with getting the timing "right" with the bitch is in the inconvenience and expense of the radioimmunoassays for LH (lutinizing hormone) and progesterone. Detection of the LH surge is the most reliable indicator for timing the breeding in bitches and is the point that proestrus becomes estrus. The LH peak is very short in the bitch, sometimes less than 12 hours. These peaks can be missed with testing done every 24 hours. Testing every 12 hours certainly is a little impractical, therefore you would still need to perform the progesterone assays to confirm that ovulation has occurred.

Ovulation occurs after the LH surge but canine eggs (oocytes or immature eggs) ovulate in a more immature state than other mammals. They have to complete a second reduction division of meiosis before becoming a normal haploid egg and fertilization can occur.

With all these processes occurring, it takes several days for a canine oocyte to become fertilizable, at least three to four days after the LH surge. However, within two days after they have matured to a fertilizable state, the gametes begin to degenerate. The upshot of all this is that the bitch is only fertile for about four days during her whole cycle if all the eggs are ovulated at nearly the same time. It is, however, fairly common for the eggs to be ovulated over a 18 - 36 hour period thus lengthening the fertile period.

In conjunction with the LH surge  the formation of the corpus luteum increases the progesterone level. Before ovulation and the formation of the corpus luteum, progesterone is produced by the follicles and may cause a reading as high as 2ng/ml serum progesterone.

ICSB research has found that ovulation usually occurs at about the time that the progesterone level reaches 5ng/ml in the blood serum. The procedure we use for timing the bitch for artificial insemination relies on serum progesterone.  If the bitch shows the average length of estrus and is proven, we normally wait until the 7th or 8th day of estrus (day one being the first appearance of red vaginal discharge) to start the progesterone testing.  If the bitch's progesterone is still at baseline (less than 1.8 ng), we skip a day to do the next blood draw.  Once the bitch rises to 2.0ng, daily serum progesterone is run until the level rises to 5.0 ng.  The most accurate test for progesterone is the numerical level report.  The in-house color tests can be used, but the interpretation of results may not be very accurate. When the bitch's progesterone rises to 5.0 nanograms, we plan the breeding(s) as follows:

If vaginal inseminations are used, usually two AI's are performed.  The first AI we do two days' following the point when the progesterone is at 5.0 ng, then the second AI four days' following the point where the level is at 5.0 ng.

If surgical insemination is used, the AI is done late on the 2nd day, or on the third day, following the rise to 5.0 ng.

If the progesterone is above 5.0ng when the first test is performed, the breeding should be done when the bitch is at 15 nanograms, plus or minus 3-4 ng. If you miss the window at 5.0 nanograms, then you would hope to catch her at between 9 and 12 nanograms the day prior to breeding.  The progesterone level should be within the the prime breeding time.

Unfortunately getting this two to three day timing just right for a particular bitch is, as I noted above, inconvenient, but it remains the best way to determine the proper time to do the artificial insemination and to insure that the semen is placed in the bitch when she is most fertile.