One of the questions that clients ask me very often is about the reproductive cycles of their pets. There are many people who do not have clear concepts as to what season, menstruation, psychological pregnancy, and breastfeeding mean. In addition they compare the women’s cycle with that of their cat or dog.
The reproductive cycle of women, and some other primates such as the chimpanzee, is a menstrual cycle that lasts about a month (from the Latin menstruus: monthly.) The menstrual cycle of women is characterized by a spontaneous bloody flux produced by the necrosis of the endometrium, which we commonly call menstruation or period. Approximately halfway through the cycle, the ovaries release one or more eggs, i.e., ovulation occur. In a few days the egg must be fertilized, if there is no fertilization, approximately two weeks after, the vascularised tissue that covered the walls of the endometrium falls, causing menstruation. But if the fertilization of the egg occurs then it will undergo a pregnancy.
To better understand the functioning of the reproductive cycle of the rest of mammalian female it must be understood that it's an oestrous cycle, i.e. it is the period of time which includes between the appearance of the oestrus or heat and the next. These females cycle is governed by changes in hormone levels and is presented by stations, not months. The frequency of submission of heat depends on species, ambient temperature and nutritional conditions.
The reproductive cycle of the dog.
The bitch is a seasonal monoestrus female that can have one or two heat periods per year. It is very important to be clear that the bitches have no menstruation. They have a period of time, which usually coincides with the Proestrus and sometimes oestrus, which it a bleeding and a vaginal discharge could be observed. These discharges have nothing to do with the period and are the result of the high level of hormones and increased vascularisation occurring in the area to encourage copulation and fertilization. The cycle of the dog has basically four stages:
1 Proestrus: The sexual inactivity (anestrus) is followed by the proestrus, identified by enlargement of the vulva and a muco hemorragic vaginal discharge. Although the dog attracts males through games and small leaks, it has the vagina covered with the tail and does not accept mounting showing the teeth. The average duration is 9 days (range 2-27 days).
2 Oestrus: Oestrus, is the period in which the dog accepts the copula, the vulva is still more increased in size and turgid, and with a discharge usually straw colour. The average duration is 9 days (range 3-21 days).The behavior changes from being aggressive to being totally passive. It occurs in the transition from the proestrus to oestrus, that the peak of LH and ovulation occurs within 24 to 48 hours of peak, is also established in the literature that is approximately two days from when the oestrus begun . This is the phase in which the owner must be most careful.
3 Metaestrus(Diestrus): If no pregnancy occurs oestrus is followed by the metaestrus, where the female is no longer attractive to the male by a marked effect of high progesterone in blood. The average length of this metaestrus stage is 90 days (range 60-110 days). If fertilization has occurred this phase will entail the gestation;
As a consequence of the bitch’s long exposure to progesterone when she’s not pregnant, she’s prone to a condition called pyometra if not spayed. Pyometra occurs when the uterus fills with bacteria and white blood cells. If untreated, pyometra can lead to fatal illness due to toxins secreted into the blood stream or the uterus actually rupturing. Thus, it’s highly recommended to spay a bitch that will not be used for breeding. In diestrus, the vaginal discharge will cease and the epithelial cells of the reproductive tract quickly appear small and round again. White blood cells can be seen in very high numbers during the first few days of diestrus. This is normal since their function is to clean up the cellular debris left behind by estrus.
4 Anestrus: Period of sexual inactivity, whose duration is variable with an average of 75 days. At this stage the ovule is resting, sex hormones are at very low levels.
The pseudo-pregnancy, is a both pathological and physiological stage that many bitches suffer. All female dogs exhibit some form of pseudo-pregnancy after they come out of the heat. In most cases it will go unnoticed, however some dogs will show marked changes as a result of high progesterone levels. At this stage, and due to a high level of progesterone, whether it has carried out a gestation as if not, the body of the dog is preparing for motherhood. These high levels of progesterone cause in the dog a mothering behaviour. You can see an increase of the size and temperature of the breast, sometimes come to produce milk, behaviour of nesting, aggressiveness, anorexia, etc.
The reproductive cycle of the cat
The cat is seasonally poliestrous, largely dependent on the photoperiod; it tends to occur during certain months of the year (February to October). The natural breeding season of the cat includes spring and summer, and during it, the cat presents successive estrous cycles, until there is no ovulation. Cat presents a particularity, and has ovulation induced by mating, i.e. mating stimulates the ovary to produce the egg, increasing the chances of a successful fertilization.
The heat of the cat is known for its disturbing manifestations: they are very restless, they become more loving, seek to be pampered and rub head and neck by inanimate objects and the owner
They urinate frequently, take an arched position, with the tail to one side and make loud noises.
If there is mating, the heat behaviour stops and starts the gestation, if not in a few days the mating
behaviour will reappear until the end of the breeding season.
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