Ovulation in Dogs. How Many Eggs Are Released?

Introduction

Dog ovulation is when a mature ovarian follicle bursts and releases a mature egg for potential fertilization. It is a key process in the canine estrous cycle and is very important for breeding dogs. Timing ovulation properly can improve the chances of conception occurring after mating.

Understanding when a female dog ovulates helps breeders determine the optimal days for breeding to achieve pregnancy. It allows them to pinpoint the fertile period when the female is most likely to conceive. Poor timing of breeding relative to ovulation is a major cause of infertility in dogs.

Knowing the typical signs of ovulation, such as changes in vaginal cells, hormones, and behavior, also helps breeders identify when it is taking place. Careful monitoring of the female’s cycle ensures mating happens at the right moment to increase the likelihood of fertilization. Overall, a strong understanding of ovulation facilitates successful breeding in dogs.

The Estrous Cycle

The estrous cycle in dogs occurs approximately every 6-8 months and involves four distinct stages: proestrus, estrus, diestrus, and anestrus. During this time, the female dog’s reproductive system prepares for pregnancy by developing mature ova and becoming receptive to mating with males.
female dog in proestrus stage of cycle

The proestrus stage lasts approximately 6-11 days and is when the reproductive tract starts preparing for pregnancy. In this stage, estrogen levels rise, the vulva swells, and bloody vaginal discharge occurs. The dog will not accept mating at this point.

Next is the estrus stage which lasts around 5-9 days. This is when the female is receptive to mating with males and has peaked estrogen levels. Signs include swelling of the vulva, clear vaginal discharge, and frequent urination. The dog will “flag” her tail and allow mating.

After estrus comes the diestrus stage which is the longest, lasting 56-100 days on average. If pregnancy occurs, this is when it will develop. If not pregnant, the lining of the uterus is reabsorbed. The vulva returns to normal size and there is little vaginal discharge.

Finally, the anestrus stage is a resting period of around 4-5 months where the reproductive system is inactive. Hormone levels drop and the female will not come into heat. The cycle then repeats with proestrus once again.

Overall the estrous cycle prepares the canine female’s body for potential pregnancy through changes in hormone levels, physical signs, and behavioral receptiveness to mating. The total cycle lasts on average 6-8 months in dogs.

When Does Ovulation Occur?

In most dogs, ovulation occurs 2-3 days after the onset of estrus or the standing heat. This is when the female dog allows mating. Some sources indicate ovulation happens around day 5-14 of the estrus cycle, or about 2 days after the LH hormone surge. The window of ovulation lasts for around 1-2 days (Estrous Cycle of Various Speces Flashcards, Canine Breeding Management JP Flashcards).

Ovulation is triggered by the LH (luteinizing hormone) surge and marks the end of the follicular phase when the ovarian follicles rupture and release the eggs. This LH surge occurs after serum estrogen levels reach a peak threshold. The eggs only remain viable for fertilization for about 48 hours after ovulation.

Therefore, the fertility window lasts up to 5 days but is very short, making precise timing of breeding or artificial insemination important for conception. Ovulation predictor testing kits that detect the LH surge help breeders determine the optimal timing.

Signs of Ovulation

A dog’s body provides several physical and behavioral signs that indicate when she is ovulating. These signs can help owners and breeders determine the optimal time for breeding. Some of the most common ovulation signs include:

female dog flagging tail as enters estrus

  • Swollen vulva – The vulva will appear swollen or enlarged. This occurs due to increased blood flow to the area in preparation for ovulation.

  • Discharge color change – The normal clear discharge from the vulva will turn pinkish in color. This is caused by blood vessels bursting around the vulva.

  • Tail flagging – The dog will hold her tail off to the side and flag it, exposing her vulva. This behavioral change invites mating.

  • Increased urination – More frequent urination can indicate the dog is ready to breed and ovulate.

  • Restlessness – Some dogs become more restless, clingy, and vocal when they are fertile and ready to ovulate.

  • Standing heat – The dog will adopt a standing posture with her hind legs rigid when breeders attempt to mount her.

Paying close attention to these signs of ovulation can help pinpoint the 2-3 day fertile window for breeding success.

How Many Eggs Are Released?

During a normal ovulation, most healthy dogs will release multiple eggs, ranging between 4 to 9. The average number is around 7-8 eggs per ovulation (ref: Citations 1).

Some factors that can influence the number of eggs released include the breed, age, and general health of the dog. Smaller dogs tend to release fewer eggs, while larger breeds ovulate more. Younger and middle-aged dogs also tend to release more eggs compared to senior dogs.

Additionally, ovulation count can also be lower in dogs with health issues like hypothyroidism or hormonal imbalances. Environmental factors like stress and poor nutrition can further impact egg production. However, in most healthy dogs, releasing 4-9 eggs is considered normal during an ovulation cycle (ref: Citations 2).

Factors Affecting Egg Count

The number of eggs a dog ovulates can vary based on several factors including age, breed, and size. According to Tsutsui (1989), smaller breeds tend to release fewer eggs compared to larger breeds. Small breeds like Chihuahuas may only ovulate 1-2 eggs per cycle, while larger breeds like Labradors often ovulate 5-10 eggs.

A dog’s age also impacts ovulation, with younger dogs in their prime reproductive years ovulating more eggs than older dogs. Songsasen (2007) notes that peak egg production occurs around 2-5 years old for most dogs. After age 7-9, the number of ovulated eggs declines as fertility decreases.

Additionally, some dog breeds are predisposed to releasing more or fewer eggs based on their genetics. Herding breeds like Collies and Shepherds tend to be more prolific, ovulating 8-10 eggs per cycle. In contrast, terrier breeds often ovulate fewer eggs on average.

Ovulation Testing

There are a few different methods breeders can use to test for ovulation in dogs:

  • Progesterone testing – Blood tests measuring progesterone levels can pinpoint ovulation. Progesterone peaks 1-2 days after ovulation occurs. Samples are taken every 1-2 days to identify the spike. This is the most accurate way to identify ovulation but also the most invasive. Source
  • veterinarian performing blood test to detect ovulation

  • Vaginal cytology – Vaginal cells are examined under a microscope around the expected time of ovulation. The percentage of cornified epithelial cells spikes at ovulation. This method involves daily testing.
  • LH testing – A rise in luteinizing hormone signals impending ovulation. LH levels can be measured in blood or urine. Testing daily is needed to detect the LH surge.
  • Observation – Physical signs like vulvar swelling and discharge changes may indicate ovulation is approaching. This method is less reliable than other testing methods.

Accurately timing breeding around ovulation maximizes the chance of conception. The most fertile window is over a 2-3 day period surrounding ovulation. Frequent testing in the lead-up to ovulation helps pinpoint this window.

Importance of Timing

Timing mating during a dog’s ovulation window is crucial for conception. According to the AKC, dogs ovulate an average of 48 hours after the luteinizing hormone (LH) surge, which is considered Day 0 [1]. The eggs can be fertilized for only a short window of 12-48 hours after ovulation [2]. Therefore, to maximize the chances of conception, breeding should occur within this short fertility window.

Breeding too early, before the LH surge, will likely result in failure to conceive since the eggs are not yet released. Breeding too late, more than 2 days after ovulation, will also likely fail since the eggs will no longer be viable [3]. Precisely identifying the LH surge and timing breeding accordingly is the best way to ensure the sperm and eggs unite during the optimal fertility window.

Methods to Induce Ovulation

There are several medical treatments that can be used to induce ovulation in dogs:

Gonadotropins like human chorionic gonadotropin (hCG) or follicle stimulating hormone (FSH) can stimulate ovulation. These hormones act on the ovaries to trigger ovulation. According to research, hCG is effective at inducing a fertile estrus around 4-5 days after injection when given at a dose of 500 IU/kg body weight (Kutzler et al. 2005).

veterinarian giving injection to induce ovulation

GnRH agonists like buserelin or gonadorelin can cause an LH surge leading to ovulation. These drugs mimic natural GnRH produced by the hypothalamus to stimulate the pituitary gland. One study found that gonadorelin successfully induced estrus in 89% of dogs within 4-9 days (VIN News Service 2005).

Dopamine antagonists like cabergoline and bromocriptine are also sometimes used. These drugs block dopamine receptors, leading to increased GnRH and LH secretion from the pituitary. However, research on efficacy in dogs is limited (Kutzler 2005).

Conclusion

The estrous cycle of dogs is complex, with ovulation being one of the most critical stages. On average, dogs ovulate and release 5-10 eggs during the 24-48 hour ovulation period. However, the number of eggs released can vary greatly based on factors like the dog’s age, breed, and reproductive health. Careful monitoring of a dog’s cycle is important for breeding purposes or health management. By observing changes in behavior, discharge, and hormone levels, ovulation can be detected and timed appropriately. With this knowledge of a dog’s biology, owners and breeders can make informed decisions for their dogs’ wellbeing.

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