Age of puberty can vary from 4 - 18 months.  The main factor influencing onset of puberty is day length, with puberty usually starting when the hours of daylight increase i.e. in the spring.  This seasonal control is under the influence of the hormone melatonin, produced by the pineal gland.  Higher levels of melatonin are produced during darker periods.  Breed may also have some effect on the onset of puberty, with long haired breeds, e.g. Persians, tending to come into season later than short-haired breeds, e.g. Siamese and Burmese

When cats come on heat, the main hormone responsible for the clinical signs is oestrogena steroid hormone produced primarily by the ovaries that stimulates changes in the female reproductive organs during the oestrous cycle and promotes the development of secondary sexual characteristics..  This is produced by follicles on the ovaries.  Follicle development is stimulated by a Follicle Stimulating Hormone (FSHFollicle stimulating hormone; produced by the anterior pituitary gland and stimulates maturation of the ovary prior to ovulation) produced from the pituitary gland.

Pro-oestrus:

• lasts 1 - 4 days
• no significant external signs visible and no discharge
• associated with calling but non-acceptance of male.

Clinical signs of pro-oestrus calling include rubbing against objects, rolling around, increased affection and increased vocalisation/ howling.  If stroked across the back, the cat will adopt the mating posture, i.e. forelegs crouched, hind end raised and tail deflected with paddling movements of the limbs.  Male cats will be attracted to her.

Oestrus:

• follows pro-oestrus and lasts 2-6 days
• associated with calling, attempts to escape and acceptance of male

What follows oestrus depends on whether a successful mating, ovulationthe release of an egg cell (ovum) from the ovary in female animals and/or fertilisation occur as follows:

Ovulation:

• the cat is an induced ovulator, i.e. repeated and multiple copulations over a short period of time are usually required for ovulationthe release of an egg cell (ovum) from the ovary in female animals to take place
• mating stimulates the release of the hormone Gonadotrophin Releasing Hormone (GnRHGonadotropin release hormone; responsible for the release of FSH and LH from the anterior pituitary gland) from the hypothalamus which, in turn, stimulates the release of Luteinising Hormone (LHLuteinising hormone; produced by the anterior pituitary gland and triggers ovulation) from the pituitary gland and a subsequent LHLuteinising hormone; produced by the anterior pituitary gland and triggers ovulation surge.  As with the bitch the LHLuteinising hormone; produced by the anterior pituitary gland and triggers ovulation surge stimulates ovulationthe release of an egg cell (ovum) from the ovary in female animals to occur
• after ovulationthe release of an egg cell (ovum) from the ovary in female animals the cat goes out of heat within 24 - 48 hours, the ovaries develop into the progesteronea steroid hormone secreted by the corpus luteum of the ovary that maintains pregnancy and promotes the development of the mammary glands.-producing corpus luteumLiterally means “yellow body” and is responsible for progesterone production within the ovary and progesteronea steroid hormone secreted by the corpus luteum of the ovary that maintains pregnancy and promotes the development of the mammary glands. starts to increase.

Metoestrus:

This phase of the reproductive cycle is associated with high levels of progesteronea steroid hormone secreted by the corpus luteum of the ovary that maintains pregnancy and promotes the development of the mammary glands., produced from the corpus luteumLiterally means “yellow body” and is responsible for progesterone production within the ovary.  In the Queen, the length of this phase depends on whether fertilisation occurs as follows

Fertilisation occurs

• high levels of progesteronea steroid hormone secreted by the corpus luteum of the ovary that maintains pregnancy and promotes the development of the mammary glands. are initially produced from the corpus luteumLiterally means “yellow body” and is responsible for progesterone production within the ovary.  The levels start to decrease from around day 25-35 after mating and decline slowly until day 60.  Progesteronea steroid hormone secreted by the corpus luteum of the ovary that maintains pregnancy and promotes the development of the mammary glands. is essential for the maintenance of pregnancy, which lasts for 64 days from mating
• prolactina hormone released from the anterior lobe of the pituitary gland that stimulates the secretion of progesterone by the corpus luteum and initiates and maintains lactation. is produced from the anterior pituitaryThe front portion of the pituitary gland, which is found at the base of the brain gland and levels start to increase from around day 25 after the first mating, reaching a maximum level a few days before parturitiongive birth, after which it increases dramatically during lactation.  Prolactina hormone released from the anterior lobe of the pituitary gland that stimulates the secretion of progesterone by the corpus luteum and initiates and maintains lactation. is essential in supporting and maintaining progesteronea steroid hormone secreted by the corpus luteum of the ovary that maintains pregnancy and promotes the development of the mammary glands. production from the corpus luteumLiterally means “yellow body” and is responsible for progesterone production within the ovary in the last 2/3 of pregnancy.  Prolactina hormone released from the anterior lobe of the pituitary gland that stimulates the secretion of progesterone by the corpus luteum and initiates and maintains lactation. is also essential for mammary gland development and lactation following parturitiongive birth.  In the last week of pregnancy, prolactina hormone released from the anterior lobe of the pituitary gland that stimulates the secretion of progesterone by the corpus luteum and initiates and maintains lactation. production is partly stimulated by an increase in oestrogena steroid hormone produced primarily by the ovaries that stimulates changes in the female reproductive organs during the oestrous cycle and promotes the development of secondary sexual characteristics..
• after weaning, if still in the breeding season, oestrous usually starts 10-15 days after weaning but can be as soon as 10-15 days after kittening.  Matings which occur during this first oestrous are often infertile but subsequent cycles will be fertile and it is not uncommon to see a nursing queen which is pregnancy again before weaning

Fertilisation does not occur

• without fertilisation, the corpus luteumLiterally means “yellow body” and is responsible for progesterone production within the ovary will still develop and produce progesteronea steroid hormone secreted by the corpus luteum of the ovary that maintains pregnancy and promotes the development of the mammary glands..  However, from day 25, the progesteronea steroid hormone secreted by the corpus luteum of the ovary that maintains pregnancy and promotes the development of the mammary glands. levels decline more rapidly than during pregnancy.  This is thought to be due to a lack of support from the embryo or placenta, which produces factors that help to maintain the corpus luteumLiterally means “yellow body” and is responsible for progesterone production within the ovary. The luteal phaseanother term for metoestrus in these cases last between 30 – 45 day.  This is shorter than the luteal phaseanother term for metoestrus during pregnancy (unlike in the bitch) and this is called pseudopregnancy.
• unlike in the bitch, pseudopregnancy is not associated with prolactina hormone released from the anterior lobe of the pituitary gland that stimulates the secretion of progesterone by the corpus luteum and initiates and maintains lactation. production and therefore no behavioural changes or lactation.
• at the end of the pseudopregnancy, a brief period of interoestrous (see below) will precede the next return to oestrous (if still in the breeding season)

Unsuccessful Mating:

• if mating, and therefore ovulationthe release of an egg cell (ovum) from the ovary in female animals, does not occur, the follicles break down and oestrogena steroid hormone produced primarily by the ovaries that stimulates changes in the female reproductive organs during the oestrous cycle and promotes the development of secondary sexual characteristics. levels decline
• she will enter a period of interoestrous or anoestrous (if not in the breeding season)
• in the absence of mating, heat periods are observed every 21 days during the reproductive season.

Interoestrus:

Interoestrous refers to the phase during the breeding season, either between seasons or following pseudopregnancy/ pregnancy.  It is associated with no physical or behavioural signs.

Anoestrus:

• this is a time of little ovarian activity and occurs from late Autumn/ Early Winter until Spring time, during which time the queen will not come into season
• this may be absent in cats submitted to constant long light days, e.g. cats kept indoors.

At the end of interoestrous or anoestrus, oestrogena steroid hormone produced primarily by the ovaries that stimulates changes in the female reproductive organs during the oestrous cycle and promotes the development of secondary sexual characteristics. levels start to increase and increases in FSHFollicle stimulating hormone; produced by the anterior pituitary gland and stimulates maturation of the ovary prior to ovulation are once again responsible for the induction of follicular growth and return to oestrus.