Physical Changes During The Estrus Cycle
Likewise, you will notice that the decrease in size of the vulva after estrus to its normal, almost prepubertal, size only takes place in the females that haven't been fertilized and always approximately 30 days after the diestrus stage begins; in those females who have already been fertilized and are currently pregnant, their vulvas will not go back to their normal size, permanently remaining somewhat dilated, relaxed and flabby. This is certainly not necessarily a sign that can confirm pregnancy, but it can make you think that maybe your dog is pregnant, which should lead you to taking your dog to the veterinarian. Another aspect that accompanies the stages of proestrus and estrus, and as we already know, is vaginal discharge accompanied by blood, although we also know that there can be female dogs that develop the so-called "silent or white heats" in which there is no trace of hemorrhage.
Lack of information many times attributes hemorrhage to the rupture of blood vessels although that is generally not the case; in fact, what really happens is that during heat, blood transcends the uterine walls in the preparatory stage of ovulation because estrogen stimulates the supply of blood to the over dimensioned uterus and the blood cells get lost in a process that is called "diapedesis" (Passage of blood cells -- especially white blood cells -- through intact capillary walls and into the surrounding tissue).
The amount of blood loss or the color of the hemorrhage vary enormously from one female to another and even from one heat to another, although it is true that you will almost always notice a change in color and consistency in the hemorrhage (hay yellow and a more liquid flow) according to how close you are to the moment of ovulation and moment of acceptance. Even as a female dog gets older, the hemorrhagic loss seems to diminish little by little, but it also has been proven at there is a genetic factor (running in the female side) that determines whether the female dog will bleed a lot or not or it they will have frequent heat cycles.
