by Mary Ann Sheller, DVM
Ovulation timing is a valuable tool in any breeding program. It allows us to determine when to breed a bitch to optimize the chance for pregnancy, as well as achieve pregnancy in many bitches thought to be infertile. Timing is essential for specialty breedings like fresh-chilled and frozen, and can also help us accurately predict due dates.
It will help you to understand the bitch’s estrus cycle. As you probably know, female dogs come in heat about twice a year. The heat (or estrus) will last about 3-4 weeks, and in the normal course of breeding, the bitch will stand to be bred somewhere between 8 and 15 days along. This varies a lot, however, and some bitches need to be bred as early as 5-6 days, others as late as 25-30.
The three most important hormones in the bitch's estrous cycle are L H, progesterone, and estrogen.
Estrogen is the hormone that causes the bitch to act receptive. Estrogen causes the vulvar swelling, the bleeding, and the changes in the vagina that many veterinarians use to do "smears." In the average bitch, estrogen rises anywhere from 4 to 20 days before ovulation. Because of this very wide range, estrogen levels are only a very rough estimate of when the bitch will be fertile. Estrogen plays no actual role in causing ovulation.
LH is luteinizing hormone. LH actually causes ovulation. It is normally at very low levels in the blood, then suddenly surges and drops back to near zero again. Two days later, ovulation occurs, and then the eggs must mature for two more days before they become capable of being fertilized. The eggs are mature for two to three days, after which they deteriorate and die if they have not been fertilized. Therefore, if you considered the LH peak to be day zero, the eggs can be fertilized four to seven days later.
It is possible to test for the LH level, and this is actually the most accurate way to do it. However, since LH is only elevated for a short time (as little as 18 hours), daily blood testing is required, so this isn’t nearly as practical as our other alternative, progesterone testing.
Progesterone is also normally at very low levels, then as the heat progresses, progesterone will rise fairly abruptly. It remains elevated for 8-9 weeks (the duration of a pregnancy) whether or not the bitch is pregnant or was bred. At the end of the pregnancy (or non-pregnancy), the progesterone drops abruptly. This sudden drop causes labor to start and is also responsible for the symptoms of false pregnancy, which are often seen in dogs. In fact, all bitches to go through false pregnancy with every heat cycle, some just exhibit signs more blatantly than others do.
The way we use progesterone for ovulation timing is to look at the initial rise from baseline levels. This rise occurs within a day or two of the LH surge. There is some variation, but the general rule is that the rise in progesterone from below 2.0 to above 2.0 occurs approximately at the time of the LH surge. The level will reach about 5.0 the day of ovulation and should be in the 8.0 to 12.0 range when the eggs are fully mature. Because progesterone continues to rise (verses a quick surge) it can be done every two to three days in most cases. This type of ovulation timing is used for many reasons…fresh chilled and frozen breeding, infertility evaluations, natural breeding with limited stud access, and breedings with older males or dogs with poor semen quality.
As previously stated, the LH surge is the most important event in determining fertile period, breeding or insemination timing, and expected whelp or caesarian section date. Whether you measure LH or estimate the surge based on progesterone levels, the following time frames are important. The day of the LH surge is considered to be day 0, all other times count from there.
| +2 |
Ovulation occurs (immature eggs are released from the ovaries). |
| +4 |
Eggs are mature and capable of being fertilized. |
| +7 |
Unfertilized eggs die and are expelled or absorbed by the bitch. |
| +65 |
Due date, planned c-section can be done safely on days 63, 64, or 65. |
| +2 to +6 |
Insemination times for natural breeding or fresh AI. Optimally, I will pick days 2 and 4 or days 3 and 6. Since we are estimating the LH surge for these types of breedings and fresh semen lives a relatively long time, I tend to error on the side of being a bit early. |
| +4 and +6 |
Insemination dates for fresh-chilled breeding. Again, here we are usually using Progesterone to estimate the LH surge, but because of shorter survival of the chilled semen, we cannot inseminate too early. Depending on day of the week and availability of overnight shipping we sometimes vary a bit…days 4 and 7 for instance, to accommodate a weekend. |
| +5 or +6 |
Insemination dates for frozen semen. Frozen breedings are almost always done surgically, and the timing must be precise. Progesterone levels should be done at least every 2 days so we can judge the LH surge as precisely as possible. |
Mary Ann Sheller, DVM
Vale Park Animal Hospital
2606 Valley Drive
Valparaiso, IN 46383
219-462-5785
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