Successful breeding of dogs is dependent on several factors. One of the most important factors is ovulation timing in the bitch. The reproductive or estrous cycle and timing of ovulation is influenced by several hormones.

The Hormones of the Reproductive Cycle and Ovulation

  • Estrogen - This hormone prepares the reproductive tract for breeding. It causes thickening of the lining of the vagina and passage of red blood cells from the blood vessels into the surrounding tissues. The timing for this part of the reproductive cycle varies from dog to dog and ranges from 1 to 21 days (or longer).
  • Luteinizing Hormone (LH) - This hormone is responsible for triggering ovulation. The appearance of LH in the reproductive cycle is termed the LH surge (day 0). The LH surge lasts for 24 to 48 hours. Daily blood testing is necessary to accurately identify (and not miss) the timing of the LH surge. Bitches will ovulate 48 hours after the LH surge (day 2 post LH). The eggs in the bitch have to undergo further maturation, after ovulation, in order for conception to occur. Therefore, their optimal fertile period is on days 4, 5, and 6 post-LH surge. 
  • Progesterone - This hormone is "baseline" prior to the LH surge, and begins to rise at the same time as the LH surge. By the time that ovulation occurs in the bitch Progesterone measurements range from 4 to 8 ng/ml, and then it rises to greater than 20 ng/ml (range of >20 to 40 ng/ml) when the bitch is in the peak of her fertile period. The period of time of the reproductive cycle - starting at the LH surge to the end of the fertile period - is consistent from bitch to bitch.
Other factors that can affect pregnancy and lactation in the bitch include:
  • prior medical conditions or surgeries
  • performance or work demands on the dog
  • body condition
  • level of activity
Sedentary lifestyles and being overweight can adversely impact fertility, ovulation rate, and ability to whelp normally (among other ill effects on their health). Males should also be tested to assess their health status.

The LH Surge

Monitoring the appearance of the bitch can help in predicting the timing of the LH surge. Prior to the LH surge the bitch may have significant swelling of the vulva and a dark red, bloody vaginal discharge. As estrogen drops and progesterone begins to rise (at the start of the LH surge), the swelling of the vagina and vulva will decrease. There may be a softened appearance of the skin around the vulva and a change in the discharge from a dark, bloody red to a discharge that is more straw-colored in appearance. This is not a very reliable sign because it may not be very obvious in some dogs. Veterinarians who examine bitches to assess for ovulation timing will perform vaginoscopy (inserting an instrument into the vagina to examine the tissues) to observe for changes in the appearance of the lining and tissues of the vagina.

Behavior changes
In addition to changes in the appearance of the vulva, owners may notice a significant change in the behavior of the bitch. Flagging is a specific behavior that is seen with the LH surge (on or around day 0). If the bitch is the only pet in the household, owners may notice her whining as she walks about or she may flag if someone bumps up against her. In multi-pet households, other pets may start mounting the bitch, however males are not typically that interested in the female (at that time). Male dog's interest in mounting the bitch becomes more intense on days 4, 5 and 6 post LH surge. At that time, the males may lose interest in eating and may vocalize more intensely for the females.

Breeders who maintain records will typically note the timing of the first day of heat, the day that the bitch dramatically begins to stand (for mounting), the days that males begin to cry for the bitch, and finally, the day that the bitch loses interest in breeding. When a bitch begins to stand for being mounted, she will generally be ready for breeding - starting 2 to 3 days later. As for the males, when they are crying, lose interest in eating, and become very eager to get to the bitch, it is a good sign that she is likely in the peak of her fertile period and is ready for breeding.

Predicting the Whelping Date
Bitches typically whelp 65 days (plus or minus 1 day) after the LH surge. Dogs with larger litters may whelp 1 to 2 days earlier and bitches with only 1 or 2 pups may take 1 or 2 days longer to give birth. This corresponds to whelping approximately 60 to 61 days after the breeding date.

For dogs that may need to pre-plan a C-section date, measuring progesterone in the blood can help to pinpoint the correct date to schedule the C-section. Serial progesterone measurements at the end of the heat and at breeding can be helpful for calculating the expected due date for the litter. One general guideline is that the bitch is expected to whelp 9 weeks from when the progesterone level measures 5 to 8 ng/ml.

More About The Heat and Cycle
The bitch is usually most fertile the last 3 to 4 days before she goes out of heat. Because heat cycles may vary from bitch to bitch, breeders are usually keen to keep records on the pattern for each bitch (so that they can be as prepared as possible when they are ready to breed a given bitch and plan to monitor progesterone levels).

Some dogs have short heat cycles in which they are in and out within 7 to 9 days. In these dogs, if they are bred, blood testing for progesterone levels would usually begin by day 2 or 3 of the heat. These dogs often have their LH surge at the beginning of the heat and are ready to breed 4 to 5 days into the cycle. Dogs that have heat cycles that last 10 to 12 days should have their progesterone levels checked starting by day 6 of their heat, and dogs that have heat cycles lasting 14 to 16 days should start blood testing by day 8. Some bitches will have a heat cycle lasting 21 days or longer. Breeders also need to be mindful of the flagging behavior of the bitch, as signs of the first day or two of the heat cycle may not be obvious in some dogs. If flagging is observed earlier than expected, the progesterone testing should be started earlier than was calculated.

Pitfalls of Ovulation Timing
Serial testing of progesterone is critical to monitoring for the optimal time to breed the bitch. If progesterone is not monitored through to the point of its increase (suggesting ovulation), breeders may miss the prime time for breeding the bitch. Best practices are to get a baseline level before the LH surge, and to continue monitoring until ovulation is confirmed with a progesterone level of greater than 5 to 8 ng/ml.

Monitoring progesterone levels along with detailed record keeping for each breeding bitch - including when the bitch started to show bleeding, flagging behavior, peak standing (when the male cries for her), and when she goes out of heat - are helpful for pinpointing ovulation. In addition, looking back on whelping dates for dogs is helpful for cross checking if the planned breeding date for the bitch was optimized for conception. For example, if a bitch whelps at 58 to 59 days, they were probably bred later than optimal, and if a bitch whelps at more than 62 days, they were likely bred earlier than is optimal for conceiving. This becomes an issue in dogs with fertility problems.