What happens with the female dog body after mating?

Spermatozoids must fecundate ovules that have been freed from the ovaries to form the zygotes, the origin of embryos. These zygotes placed themselves in the uterus wall for, approximately, 19 days after coupling, and from then on embryos start to develop. Uterus horns are long enough to host, and allow growing of a great number of embryos. Each one of them forms a placenta union that provides the vital nutritive substances and the oxygen, eliminating products rejected by the embryo metabolism. As there is no direct connection in the placenta, between the mother's circulatory systems and the developing puppies, she cannot transfer immunity to them, as in humans. They depend therefore, of suckling during their first days of life, to get the vital protecting immune globulin. At 33 days of pregnancy, comes the organ genesis, and in the rest of the pregnancy period, the fetuses that now are like micro puppies, grow to complete their final size. This is the period of pregnancy where the mother has more needs: 95% of the puppy's growth takes place during this period

Which is the external evidence that indicate successful mating?