When heat or heat of the bitch is called in the Kynologie certain phases of the sexual cycle in female dogs. The term is not clearly defined. It is usually used for the entire duration of the section of the sexual cycle associated with vaginal discharge (proestrus, estrus and earlier metestrus) or only for the time of proestrus and estrus in the narrower sense or for the fertile phase with the follicle cracks (estrus), in which a bitch is usually ready to mate - the actual standing heat .
Reproductive biology in dogs
The sexual maturity is variable in domestic dogs. The first heat ( oestrarche ) can occur as early as six months, but an onset age of two years is not uncommon and rarely a sign of illness.
Dogs are out-of-season, diostric animals. There is no seasonality. The heat interval is six to seven months. Small breed bitches can come into heat every four months. Dingoes and Basenji usually show only one heat per year.
Unlike humans, there is no menopause in dogs . Bitches that are older than seven years, however, come into heat less often, usually only once a year. The interval between heat increases with age.
Expiration of heat
In the bitch, a bloody vaginal discharge begins in the pre-oestrus ( Proestrus ). The vulva swells and the epithelium of the vaginal mucous membrane thickens from 2 to 3 to 15 to 20 cell layers and is oedematized . During this phase, the vaginal lining becomes increasingly pale and wrinkled. The bitch is already attractive for males in the Proestrus , but not yet ready for deck .
In the actual oestrus phase ( oestrus ), the vaginal discharge becomes flesh-colored (decrease in the red blood cell content ) and the vulvar swelling decreases. The vaginal mucosa is pale, sticky / sticky and furrowed like clods ("field"). In this phase the bitch can be covered (" standing heat "). Hormonally this phase is characterized by a decrease of estradiol - and an increase in the concentration of progesterone in blood serum characterized.
During the after-oestrus ( metestrus ), swelling and discharge decrease significantly. The discharge becomes yellowish due to the high content of neutrophil granulocytes (leukocyte clearing phase). In early metestrus the bitch can still be ready to mate.
The duration of heat is on average 18 days, 9 days each for proestrus and estrus. However, it is individually different and is largely constant in an animal from the second heat.
Disorders of heat
The absence of the first heat ( primary anestria ) is mostly due to disorders of the hormone cascade hypothalamus - pituitary- glandular glands. Of the chromosomal abnormalities , the XX reversal (an X chromosome carries hereditary information that is normally located on the Y chromosome ) is of particular importance. Here masculinization and enlargement of the clitoris occur. A breed cluster has been described for the American Staffordshire Terrier , Beagle , American Cocker Spaniel , German Shorthaired Pointer , Miniature Pinscher and Norwegian Elkhound .
The lack of heat later in life ( secondary anestriation ) can be caused by disorders of the ovarian function, but it can also occur as a result of other underlying diseases. With hypothyroidism , the high thyroid liberin level stimulates prolactin secretion and this inhibits the new cycle. In addition, less luteinizing hormone (LH) is produced. If the adrenal gland is overactive , less LH is released. If there is no other underlying disease, heat can be triggered with cabergoline or a GnRH analogue .
Shortening the heat interval
A shortening of the heat interval to less than five months can occur physiologically through contact with another bitch in heat. In addition, a luteal weakness ( hypoluteinism , syn. Progesterone insufficiency ) can be responsible. This is most common in the German Shepherd Dog , Rottweiler and Bernese Mountain Dog . The cause is not known. Progesterone antibodies in the sense of an autoimmune disease are discussed as the trigger, and in the German Shepherd Dog a deficiency of prolactin is also discussed, which in the dog has a luteotropic effect that preserves the corpuscle. When covering after a shortened cycle, regular control of the progesterone concentration is recommended, since the bitches often do not give birth without replacement of progesterone.
"White heat" or "quiet heat" is the term used to describe the absence of symptoms of heat despite the formation of follicles. Here vaginal cytology and progesterone determinations can be used to determine the time of mating.
If proestrus and estrus last less than ten days, it is referred to as a shortened heat. On the one hand, the impression of a shorter period of heat can only be based on overlooking the first symptoms of heat. On the other hand, an actually shortened heat can indicate a decreased estrogen release or a decreased responsiveness of the estrogen receptors .
A prolonged period of heat (> 28 days) can express itself in different ways:
- Prolonged Proestrus : There is bloody discharge for more than three weeks without the bitch being ready to cover. It is mostly the result of a disturbance in the secretion of gonatotropic hormones ( gonadoliberin , FSH , LH ).
- Prolonged oestrus : The deck readiness is longer than three weeks. The cause is usually the absence of the Follikelsprungs individual ovarian follicle . The hormonal imbalances often lead to glandular-cystic hyperplasia of the endometrium , possibly also a pyometra .
- Split oestrus : Here, after the onset of proestrus with discharge, males are not attractive. The actual oestrus only follows a few days or weeks later. In relation to the sexual cycle, there is a double proestrus, in which the first does not lead to an estrus. Split oestrus is most common in young bitches.
As a result of estrogen-induced edema there may be a in the heat vaginal prolapse ( Läufigkeitsprolaps come). In the case of prolonged heat, a differential blood count is recommended , as increased estrogen levels ( hyperestrogenism ), due to their negative influence on the bone marrow, inhibit blood formation, and initially cause thrombocytopenia in particular . In addition, vaginal cytology and ovarian ultrasound to clarify ovarian cysts and tumors are indicated.
- Sebastian Arlt: Menstrual cycle disorders in the bitch. In: Small Animal Practice. Vol. 61, No. 6, 2016, doi : 10.2377 / 0023-2076-61-334 . , pp. 334-346,
- Hans G. Nobody, Peter F. Suter: Internship at the dog clinic. 9th, revised and expanded edition. Paul Parey, Stuttgart 2001, ISBN 3-8263-3154-0 , pp. 859-860.
- Axel Wehrend : Key symptoms of gynecology and obstetrics in dogs. Diagnostic guide and therapy. Enke, Stuttgart 2010, ISBN 978-3-83-041076-8 , pp. 145-152.