Along with the problem of large number of kittens veterinary surgeons in the latest time face another actual problem - female cat sterility. Often this results from heredity, infectious and parasitic diseases, as well as some factors of environment.
This time we won't consider cases of pathologic pregnancy in cats caused by aborts and stillbirth for it is a topic for another article.
Before looking into the reasons of sterility in cats one should have the notion how the system of reproduction in normal female cat functions.
The age of puberty varies much. Some females reach it at four months, most of them are common stray cats or cats of oriental type. Others become pubertal much later: at 12-18 months or even at three years (as an exception) - Persian cats and their relatives. The season of birth influences the age of puberty also: a cat born in August reaches this age early - at 8-10 months, while a cat came to life in March will become mature at one year or later.
If a cat doesn't live at home its' heat is determined by daylight hours: most cycles happen in the period from February to June; these cats are to be polyestrus. Cats that live at home in conditions of regular illumination have an estrus (heat) in the course of year, that doesn't depend on season (daylight hours). Mostly, ovulation (when the egg comes out of ovary into the cavity of body) is provoked by coupling. Since ovulation can't happen without coitus, follicles (bubble-like formations containing ovule) regress, and the new cycle begins. However about a quarter of these cats are able to ovulate without vaginal stimulation - this explains pseudo sterility.
The first stage of heat is proestrus that lasts for two days. At this time cat shows signs of heat, but she still doesn't allow coupling. Then the stage of estrus follows during which a female seeks for a male and, if fails to find him, the heat continues about a week or some days more. In presence of male by the 3-4th day a coupling happens, and the period of mewing and cat songs usually reduces.
If coupling doesn't happen, the interval between heats changes (from several days to several weeks). If during coitus there was no impregnation for some reasons, the false pregnancy begins and next heat defers on 6-8 weeks.
Female genital activity depends on neuro-hormone factors. Estrogens, secreted by the follicle settled in ovary influence female behavior during estrus. Yellow body of ovary and placenta secrete progesterone, which maintains pregnancy. Progesterone is produced under the action of gonadotropic hormones, produced by hypophysis (a small gland at the base of brain). Hypothalamus also takes part in hormonal activity. This is an area in brain that is sensible to hormonal state of animal as well as external influence: light, pheromones, social contacts and coitus. When this miraculous mechanism fails a cat can't become pregnant. There are some other pathologic states, which cause sterility, most of them are the sequent of incorrect raise and keeping of animal.
The role of heredity is also important in case of sterility. Abnormalities of development (androgyny, abnormalities in genitals) or chromosomal abnormalities are one more reason.
Quite often sterility may be caused by infectious and parasitic factors. All diseases accompanied by high temperature or weakness affect the reproduction functions. Clinical forms point out the following diseases in order of significance: respiratory pathologies, accompanied by penetration of chlamydia inside genital system, urolithiasis, enteritis, coccidiosis, toxoplasmosis, anemia, panleucopenia, FIP, leucosis, herpes. Viral diseases as well as urinary disorders are especially dangerous.
Diseases of genital system also may cause sterility: refusal from coupling because of inflammation or infection of genital ducts, impossibility of implantation of ovule after impregnation because of endometritis (infectious disease of uterus).
One should feed a dam cat well; lack of nutrients causes exhaustion, yet this state is less dangerous in respect to fertility than abundant feeding that leads to obesity. Sexual activity reduces in cat with an excess weight. But an unbalanced feeding affects adversely as well: a female cat needs certain nutritious substances, especially taurin, vitamin A and basic fat acids in particular.
It may happen that the amount of hormones that are responsible for sexual activity are insufficiently secreted in organism of cat. And usually it is difficult to determine what kind of hormones is not enough and why.
Hyposexualism is the absence or insufficient display of sexual activity of cat. The reasons are usually concealed in the physiology, and, first of all, in seasonal unestrus (absence of heat). If a cat didn't have heat in the middle of June, don't expect the kittens be born three months before the New Year! Genital infantilism may also become the reason of sterility: if by the first year a cat doesn't have heat one should keep patience - she is not ready to give posterity. When sexual pause happens owing to other cat this is more dangerous, for example, when several cats live together and there is a sterile male, which couples females. Coupling, though it is inferior, may entail neuro-hormone reaction - provoke ovulation, and during following two months there will be no heat in female.
Under the unknown reason sometimes hypophysis functions poorly and this leads to hyposexualism. And, finally, this state may be caused by use of medications that prevent heat.
Hypersexualism, or nymphomania also occurs quiet often and is expressed as intensive heats lasting longer than usual. This phenomenon is caused by the excess of estrogens secreted in abnormal amounts by cysts of ovaries or, more rarely, tumors. The uterus itself may become the source of pathological state, which is called hyperplasia, or pherocyst endometritis, at which the mucous membrane of uterus thickens and loses the ability to accept a fertilized ovule. Accumulation of mucus inside uterus may cause pyometra after which female cats become sterile in 20 per cent of cases. This disease is hard to diagnose because heat has a normal course.
Besides this, often the sterility may result from incorrect keeping of cat. If your cat refuses to give you pretty kittens, think if you did something wrong and then consult with a vet.
Translated by Tatiana Karpova (Moscow)
(MSU, Biology faculture, Dep. zoology and ecology).