No, a dog is not pregnant right away after breeding. It takes time for fertilization to occur and for the embryos to develop and implant in the uterus. After a female dog is bred, it can take 1-2 days for the sperm to reach the eggs in the oviducts and then another 2-3 days for fertilization to occur. The fertilized eggs then travel down the oviducts and enter the uterus, where they will implant in the uterine lining around day 21-25 of the dog's reproductive cycle. Not all breedings will result in pregnancy, and there are many factors that can affect the success of breeding, including the timing of the breeding in relation to the dog's reproductive cycle, the quality of the sperm and eggs, and the health of the dogs involved.