Dog Estrus Cycle in Canine
During the Canine Estrus Cycle, the female dog accepts to be mated by any male, and on average it usually lasts in between eight or nine days although there have been cases of down to 3 days or up to 21 days. The vaginal discharge, when present, has a hay color and the vulva remains turgid, very warm when touched and voluminous. Besides, it is in this stage that there is less pressure on the surroundings of the vulva. As we have seen before, the levels of estradiol reached their peak in the last few days of proestrus and on the first day of estrus start to go down. The follicles or ovaries, influenced by LH start to go through important changes and the levels of progesterone start to go up moderately. It is precisely from the combination of the levels of estrogen and progesterone that the female accepts any and all males that she comes across; her secretions, precisely influenced by these hormones, become olfactorily much more attractive and irresistible for the male.
When the levels of estrogen go down and parent as he the levels of progesterone go up and, the production of LH also goes up at the same rate which stimulates the ovulation that will take place approximately 2 or 3 days after estrus begins. Is important to mention here that femaleare some of the only members of the mammal group that present this hormonal situation during estrus, because most, at this point, have already finished the estrus stage. After ovulation has taken place, the levels of estrogen keep on going down meanwhile the levels of progesterone increase significantly and rapidly.
We now know as a fact that all follicles ovulate in a short space of time (not more than 24 hours) and that the number of liberated ovules will determine the size of the litter, significantly varying according to the age, breed and size of the female. So for example there can be cases of 2 to even 20 or more ovules in every cycle. Learned breeders have also come to the conclusion that in the moment of ovulation, the ovules are immature, primary and unable to be fertilized, and they needed at least three days to reach enough maturity, in a secondary state. This justifies why the average lifespan in which ovules can be fertilized is so short (in between 24 and 48 hours -- maximum) and that conception (The act of becoming pregnant; fertilization of an ovum by a spermatozoon) usually takes place around this sixth day of estrus. Likewise, it is known that spermatozoids live approximately 3 to seven days inside the vagina and uterus of the female. This explains why, on occasions, some pregnancies seemed to stretch out longer than the 63 or 68 days normally expected for the complete process of pregnancy. Or, conversely, a perfectly healthy and fertile female does not result in pregnancy if the mating has taken place in the final stage of estrus, when the ovules are not alive anymore.
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