Canines in heat, rutting stags and felines in season: creatures make it clear when they're generally fruitful. Some of the time this includes a touch of blood. With people it's by and large the inverse.
All vertebrates have a feminine cycle. Yet, the greater part of them have a secret feminine cycle. This implies the endometrial covering is so slim; it gets totally consumed by the body if the egg isn't prepared. People, primates and some different well evolved creatures (bats, African elephant wenches and certain tree vixens) have such a thick endometrial coating that piece of it is being shed through the vagina.
The ridiculous release you find in female canines, and now and then additionally in cows and types of the pony family, has to do with the ovulation: veins in the vagina divider burst due to the pulse. This draining is no period. Plus, creatures can be very testy when they're rich. Simply ask any pony proprietor with a horse in the stable.