If you read my previous posts, you already know that, when it comes to reproduction, the canine species is really unique (if not, well, no worries, just click here!). Short recap: progesterone is secreted BEFORE ovulation in dogs and we can use this characteristic of the canine estrous cycle to determine when the bitch ovulates. This is what we refer to as “timing of ovulation”: great tool to improve fertility and prolificity in your animals since mistimed breeding is –from far- the most common cause of infertility in the bitch. When I was working at the repro center at the Alfort Veterinary School (Paris, France), these consultations were part of my daily routine. Here are 20 facts that might help you better understand what the reasoning behind it is!
Fact #1: When to start? We were recommending having the 1st consultation around 6 days after beginning of the heats. Sounds too early? Well, always better sooner than never: unfortunately, some bitches might ovulate as soon as this in their estrous cycle.
Fact #2: Very often I had clients calling me: “Doc, my bitch is at [number] in progesterone. What should I do?”. My typical answer: “ [number] what?”. Wonder why? Progesterone results can be expressed in 2 different units: ng/mL OR nmol/L. We won’t interpret a result the same way depending on its unit.
Fact #3: Sometimes, I was asked to determine when the bitch would ovulate based on a single test. Most of the time that is not possible (I told you I had bitches that ovulated 6 days after beginning of estrus, but I also had some that ovulated 30 days after!): at least 3-4 tests will usually be required.
Fact #4: “Do I need to come every single day until ovulation occurs?”. No, this might be necessary when doing LH assays (another hormone secreted by the brain which peaks 2-3 days before ovulation): LH secretion is pulsatile and we need to detect a transient peak, so that’s why daily assays are needed in this case. On the contrary, progesterone will progressively rise during estrus, and this is this rise we will focus on when performing timing of ovulation.
Fig 1: Progesterone profiles in different size bitches
Fact #5: If progesterone is low (= basal value), typically we can wait 4-5 days before seeing the animal again.
Fact #6: Progesterone is said to be “basal” when its blood concentration is below 1ng/mL.
Fact #7: See the graph above? I highlithed the two main events we need to focus on when performing a timing of ovulation: the “LH peak” and “ovulation”.
Fact #8: LH peak usually occurs when progesterone levels reach 2-3ng/mL. When this level is reached ovulation will occur 2-3 days after.
Fact #9: Never stop a timing of ovulation when you think you got past the LH peak as mentioned above! You still need to detect ovulation: some bitches might indeed do what we call an anovulatory cycle.
Fact #10: What’s an anovulatory cycle? A cycle that does not lead to ovulation (and obviously then, the bitch will not be pregnant). Progesterone might rise because of the growth of the ovarian follicles containing the oocytes, but suddenly drop (we still don’t know why), follicles will simply shrink and disappear: ovulation will not occur. I had a bitch that went as high as 4.9ng/mL in progesterone, but then dropped.
Fact #11: Ovulation occurs when progesterone blood levels reach 5-6ng/mL.
Fact#12: This value is the same whatever the size of the animal. Whether you have Chihuahuas, Labradors, English Mastiffs, etc, bitches will always ovulate around the same progesterone rate. Take a look at the graph above and you’ll see that at the time of ovulation, the different curves all superpose each other.
Fact #13: We know the progesterone rate at the time of ovulation. However, at the time of breeding, there is no “ideal” level. When fertility is optimal, progesterone values might be around 10, 30, sometimes even >60ng/mL! The breeding protocol should be determined based on the estimated day of ovulation. We cannot say that the bitch should be bred when she is at [any number]ng/mL in progesterone!
Fact #14: Why performing a progesterone test after ovulation then? Progesterone blood levels will rise quickly after ovulation, and it is good to confirm that this rise occurs. Indeed if a plateau (=progesterone levels stagnating around the same value) is observed, something is not right, and an ovarian cyst might be suspected.
Fact #15: In fact, each time such a plateau is observed during the timing of ovulation, the bitch should always be carefully followed. This can indeed happen sometimes, but a plateau should not last more than 3 days. If there is any doubt, an ovarian ultrasound should be performed, to be sure the surface of the ovaries looks normal.
Fig 2: A progesterone machine
Fact #16: The hormone “progesterone” is the same in all mammals (same conformation, same molecular size, same everything…). No need for “specific canine assays” then. To tell the truth, all the machines that are used to assay progesterone in canines are primarily developed for the human market.
Fact #17: Progesterone machines are not all the same. What I mean by that is that if ovulation rate was 5-6ng/mL on the machine I used in my clinic, it might have been 4-5ng/mL or 8-10ng/mL on another one. The value needs to be properly interpreted: it’s important to rely therefore on somebody who is used to work with the laboratory or the machine that gives the results, so they are properly interpreted.
Fact #18: There are now in-house machines that can be used in veterinary clinics to assay progesterone.
Fact #19: It usually takes 18-20 minutes to run a progesterone test.
Fact#20: You did a timing of ovulation, your bitch ovulated 17 days after beginning of her heats and she was pregnant. Does that mean that next time, your bitch will ovulate at 17 days again? Not sure at all… There are up to 40% variations between cycles. A timing of ovulation should therefore be performed at each cycle.
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