PERIODICITY OF BITCH'S HEAT
Can bitches have heat at any time of the year ? Can puppies born through the whole year ?
Physiological recall about the bitch's heat
Fist bitch's heat usually occurs between 6 and 12 months, sometimes as late as the age of 18 to 24 months-old in large breeds.
When regular, heat is usually shown twice a year, every 6 or 7 months ; in fact, the typical interestrus interval varies from 5 to 11 months in duration, with extremes observations as short as 3,5 months and as long as 13 months. Because of these physiological differences, the annual rythm is largely altered and shifted.
Main exhibited signs of heat are:
- swelling of the vulva, and vaginal bleeding that may turns into a serous discharge ;
- a change of the behaviour of the bitch towards the male: she progressively accepts his attempts for mounting.
These signs mean that the bitch is going to become receptive for beeing fertilized. Let's point out that the elapsed time between the beginning of the heat and the ovulation date varies considerably according to cases : several vaginal smears, eventually associated to a progesterone dosage, give a better chance of success for breeding.
As heats occur at regular intervals, the sexual activity of the bitch is often qualified of "seasonal" : one cycle happens in the automn/winter, another one in the spring/summer. However, it does not mean that the regulation of of the bitch's cycles is only determined by the photoperiod as it is the case for birds, horses, sheep... Duration of daylight, temperature, location could influence the ovarian cycle, but the results of studies do not agree between themselves. Moreover, only bitches kept outside would be receptive to these influences.
Other external factors of regulation interfere, even if we know very little about them. For example, within a kennel, bitches heats tend to synchronize naturally : odorous substances produced by females in heat (pheromones) are probably able to stimulate the hormonal secretion responsible for the start of a new ovarian cycle in others.
Theoritically, puppies can born at any time of the year. Practically, breeders often organize their production according to the automnal heat, in order to get weaned puppies around Christmas.
Others prefer to make the bitches whelp at spring to be able to raise the puppies outside when the temperature is nicer.
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