Female dogs can have puppies from multiple canine fathers, and not just from separate pregnancies. If you're caring for a litter of puppies and notice that a couple of the little guys look totally different from the rest, you might just be dealing with a case of two fathers for a single litter. This is known as superfecundation.
How Superfecundation Happens
When female dogs ovulate and release numerous eggs over the course of a few days, it can lead to superfecundation. When they ovulate and then mate with multiple dogs within a brief time span, the chances of becoming pregnant by more than one dog are very realistic. This isn't at all unusual for dogs, especially strays outside. Not only can litters to have two different fathers, they can have more than that, too, whether three, four, five or more.
Prevention of the Situation
If a female dog goes into heat and is willing to mate with multiple male dogs, she might just end up pregnant with a litter of half-siblings. If you don't want this to happen to your dog, consider spaying her so that she's incapable of getting pregnant in the first place. Talk to your veterinarian about scheduling the surgery. You can also make sure that your dog never shares the company of any intact male dogs, particularly during estrus.
Determining whether a female dog gave birth to a litter with multiple fathers is often easy, especially when purebred dogs are involved. If two poodles are being bred together and half of their litter comes out looking conspicuously like the intact young male fawn pug next door, then the answer is probably pretty clear. Things can get confusing, however, in cases of male dogs of the same breed. If the dog next door happens to be another poodle, or perhaps even of a similar looking breed such as Bichon Frisé, picking up on the differences might not be as simple and straightforward.
Outside the Dog World
While the idea of a litter with multiple canine fathers might seem strange to you, it's not as unusual as you might imagine. It's a regular occurrence for homeless female pets, cats included. It can also even happen to human beings, although it's markedly less common in them. Human parents of twins have discovered that their children were half-siblings due to noticing distinct differences in physical appearance after birth.