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Heat (Oestrus), Period and Fertility: What does it mean in female pets?

Updated: Mar 15, 2022

What is heat (Oestrus) in female dogs and cats?

 

Heat (Oestrus) refers to a biological event, a stage when an intact female dog or cat can reproduce and is ready to mate. At this time the body is producing mating hormones that make the female receptive to a male. The mating hormones are oestrogen, progesterone, and testosterone.

Structural Chemical Formula and Molecule Model Illustration for the mating Hormones: Testosterone, Estrogen and Progesterone.
Structural Chemical Formula and Molecule Model Illustration for the mating Hormones Testosterone, Estrogen and Progesterone.


How many stages are there in the oestrous (heat) cycle?

 

The heat or oestrus cycle has four stages, ie, Pro-oestrus, Oestrus, Dieoestrus/Metoestrous and anoestrus. Each stage has different signs related to behaviour, hormonal changes, physiologic changes, physical or clinical changes, and cytologic (cellular) changes. So, when a dog or cat is said to be in heat or in season she is in the oestrus stage when ovulation occurs and she is receptive to the male as illustrated below (Figures 1 & 2).

Canine Oestrous Infographic: VetPrep.com
Figure 1: Canine Oestrous Cycle Infographic: VetPrep.com
Cellular and hormonal changes during oestrous cycle in the female dog
Figure 2: Cellular and hormonal changes during the various stages of the oestrous cycle in the female dog

How is the oestrous (Heat) Cycle controlled?

 
Pituitary and ovarian hormones
Figure 3: Pituitary and ovarian hormones

The bitch is considered as a spontaneous ovulators, ie, ovulation occurs without any breeding stimulus, whereas queens are considered induced ovulators, i.e. ovulation is triggered by mating. Thousands of follicles are contained within the ovaries, each follicle containing an egg or ovum. At the beginning of the oestrous cycle, a group of follicles is selected and begin to develop. They both start cycling with the influence of hormones released from the hypothalamus and pituitary glands within their brains. The development of the follicles is promoted by the release of hormones from the hypothalamus (gonadotropin-releasing hormone [GnRH]) and pituitary (follicle-stimulating hormone [FSH] and luteinizing hormone [LH]). As the follicles develop, they secrete oestrogen, which causes the physical and behavioural signs of early heat, or proestrus.

The Ovary.
Figure 4: The Ovary.

Nine days after the onset of proestrus, oestrogen concentrations fall. At this time, the bitch stands to be bred (standing heat or oestrus) and a surge of LH is released, causing ovulation. This is referred to as spontaneous ovulation. Queens, on the other hand, are referred to as induced ovulators because, in this species, copulation is the most common trigger for the release of GnRH and subsequent ovulation. In either spontaneous or induced ovulators, the eggs are released from the follicles into the uterine tube, where fertilization occurs.


How long is the heat (oestrous) cycle?

 

The oestrous cycle can last anywhere between two and four weeks collectively. Oestrus is the stage when the female dog or cat can become pregnant and this varies with each individual pet. On average, the heat lasts for 1 ½ to 2 weeks though this can be shorter or longer. The pregnancy status also affects how long the diestrus stage lasts; the anestrus stage of the heat cycle is simply the resting stage that intermits the next one.



How Often Are Dogs in Heat?

 

Female dogs often go into heat once every six months. However, the breed size of the dog also affects the frequency of the cycle: a smaller dog goes into heat more often than a larger dog, and a dog’s heat cycles may seem irregular in the beginning. Besides, dogs are induced ovulators, meaning they are able to bear puppies from multiple fathers in one litter!


How Often Are Cats in Heat?

 

Cats are polyestrous, which means they go into heat several times a year. Heat (oestrus or estrus) cycles in cats start as early as four or five months in the female kitten and repeat every two to three weeks until the cat is spayed or becomes pregnant. Each heat (Oestrous) generally lasts on average, six days. If the queen is not mated during estrus, she goes out of the heat for a short period of time. Another thing to remember is that cats, just like dogs, are induced ovulators, and are also able to bear kittens from multiple fathers in one litter!


Do cats and dogs undergo a menopause?

 
Menopause illustration
Fig. 5: Menopause

Dogs and Cats do not undergo menopause and continue to have oestrous (heat) cycles for their entire life and produce puppies and kittens throughout their lives. Most cats and dogs are capable of becoming mothers around the age of 6 months. Female cats and dogs continue to experience heat cycles throughout their lives up until death, but the time between each cycle will increase with age.



When does a female cat or dog have her first oestrous (heat) cycle?

 

A female cat or dog can first experience her heat cycle as early as six months of age. However, this varies with breed. A smaller dog may experience her heat cycle earlier (about 4 months old) than a larger dog, who may not experience theirs until up to eighteen months or two years of age. Even though at six months they are old enough to get pregnant, young dogs and cats aren’t yet fully matured. Waiting until after the second estrus cycle promotes a healthy pregnancy.


When is a dog most fertile during heat (Oestrus)?

 

The time of mating is extremely critical and it is highly recommended that the female be tested to determine the optimal days for breeding. For most females, the best time for breeding is between the ninth and the fourteenth day of estrus. However, some females ovulate as early as the third or fourth day or as late as the eighteenth day. Blood tests or vaginal cytology adequately assist in determining the best period for mating a dog.

Figure 2: Cellular and hormonal changes during the various stages of the oestrous cycle in the female dog
Figure 6: Cellular and hormonal changes during the various stages of the oestrous cycle in the female dog

What are the signs of heat (Oestrous) in cats and dogs?

 

Cats:-

Behavioural signs are the most notable signs of oestrus (heat) in cats. These behavioural changes can be upsetting to owners, with some of them thinking that their cat is unwell.

The most common signs of a cat in heat are:-

  1. Vocalizing

  2. Urine spraying

  3. Attention-seeking behaviour

  4. Demanding or pushy behaviour

  5. Rolling on the floor

  6. Raising hind end into the air

  7. Wiggling hind end when the back spine is stroked

  8. Begging to go outside

  9. Rubbing its face on things

Signs your cat is in heat (The Spruce / Lara Antal: www.thesprucepets.com
Figure 7: Signs your cat is in heat (The Spruce / Lara Antal: www.thesprucepets.com)

Dogs:-

In the dog, each phase of the heat cycle has different changes, and these may include the following signs:

  1. Swollen vulva

  2. Bloody or straw-coloured discharge from the vulva

  3. Receptive to male dogs

  4. Excessive licking of the genital area

  5. Agitated, nervous, or aggressive behaviour

  6. Urinating more frequently

  7. Change in tail position


Signs your dog is in heat (The Spruce / Lara Antal: www.thesprucepets.com)
Figure 8: Signs your dog is in heat (The Spruce / Lara Antal: www.thesprucepets.com)

What does one do if a cat or a dog Is in Heat?

 

Cats:-

  1. Every cat is different, some prefer to hide when stressed, while others prefer fussing and cuddling. Providing a safe, quiet place, a cosy cat bed with a few blankets, or even a cardboard box for her can help ease the stress of being in heat.

  2. Diffusers, e.g. Feliway, help to keep patients calm! It can be a plug-in diffuser or even a spray.

Dogs:-

  1. Never let the dog out in the compound alone, a stray dog may mate your female dog.

  2. Never let the dog off her leash when she’s in heat, her hormones are in control and her intent on finding a male cannot be controlled.

  3. Ensure the dog’s ID tags and microchip information are up-to-date to ensure the ease of reunion, i.e., legible, updated ID tags and current microchip information.

  4. Consult a veterinarian if signs of illness are noticeable, e.g., after a heat cycle, some female dogs experience health issues with the uterus producing more fluid, creating an ideal environment for bacterial growth. This leads to a life-threatening pyometra or uterine infection causing the female dog to drink or urinate excessively, producing thick vaginal discharge, or have a decreased appetite, abdominal pain, vomiting, or lethargy.

  5. Consider spaying the dog after her heat cycle is over if there are no plans to breed the dog.


Heat (Oestrus) and gestation (pregnancy) periods

 

Description Time Mean

 

Age at the appearance of first estrus 6 -18 months


Length of estrus cycle in unmated animals Every 5-12 months 7 months


Duration of pro-estrus 3-17 days 9 days


Duration of estrus 3-21 days 9 days


Duration of estrus period (pro-estrus + estrus) 3-21 days 18 days


The first occurrence of estrus after parturition 5-8 months


Gestation period 58-71 days 63 days


Number of young Small breeds: 2-4

Medium breeds: 6-10

Large breeds: 8-12

Suckling period 3-6 weeks



References

 

Gudermuth, D. F., Newton, L., Daels, P., & Concannon, P. (1997). Incidence of spontaneous ovulation in young, group-housed cats based on serum and faecal concentrations of progesterone. Journal of reproduction and fertility. Supplement, 51, 177–184.


Lawler, D. F., Johnston, S. D., Hegstad, R. L., Keltner, D. G., & Owens, S. F. (1993). Ovulation without cervical stimulation in domestic cats. Journal of reproduction and fertility. Supplement, 47, 57–61.


Eske, J. (2019, April 5). What to know about female sex hormones. (D. Weatherspoon, Editor) Retrieved February 21, 2022, from Medical News Today: https://www.medicalnewstoday.com/articles/324887#hormonal-imbalance.


VetPrep. (2017, Dec 11). The Oestrous Cycle. The Oestrous Cycle. Retrieved from https://mobile.twitter.com/VetPrep/status/940298242385960962




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