Puppies within the same litter can vary, some are bigger than others and there can be colour variation too. But occasionally pups may seem so different that you might wonder if they are even from the same father! In this article, we explore whether this is something that can actually happen as well as some information on dog breeding generally.

Dog breeding

Once female dogs reach maturity they start to have oestrus cycles which means that they can start reproducing. When a dog is in oestrus (or having a season) she is ready to be mated and is receptive to advances from males. This usually occurs on average once every 6 months. During this time she will have a bloody vaginal discharge and puffy vulva. Most dogs will be on heat for an average of a week and a half to two weeks, with ovulation (release of her eggs) occurring when her vaginal discharge is more of a pinky-red colour and watery consistency.

Some female dogs will stand for a male more than once during their fertile period. Sperm can also survive in the bitches reproductive tract for several days. This means that if she was mated ahead of ovulation she could still get pregnant once those multiple eggs are released.

So, can puppies in the same litter have different fathers?

Yes! Female dogs can be mated by more than one dog during their fertile period meaning a mixture of sperm is present and waiting to fertilise her eggs when she ovulates. The technical term for this is superfecundation. This can also happen in other species, including humans where fraternal twins could each have a different father.

How can I tell if puppies in the same litter have a different father?

In some cases, it will be very obvious if puppies are from a different litter. For example, if you were intentionally mating your purebred Labrador with another Labrador, and some of her puppies look like labs but the others come out looking like poodles, then a mismating could have occurred! Your female dog may have been accidentally being mated by a poodle as well as the intended labrador during her fertile window.

However, if your dog was mated by two different sires of the same breed then you may not actually realise that the litter contains a mixture of DNA unless you saw both of the matings take place or they were planned.

So some litters you may not be able to tell without DNA testing whereas others are a bit more obvious!

How could this have happened??

Most of the time matings are very controlled affairs with breeders being aware of their bitches fertile period and only allowing them to mate with the male stud dog of their choice. However, accidents can happen! If your female dog escapes and gets out of your garden or runs off on a walk then a mismating could occur. Female dogs give off very strong scent signals, so an entire male dog could very quickly find and mate her.

Accidents happen very commonly within households too. If you have a mixture of entire male and female dogs then a mismating is much more likely to happen, despite your best efforts to keep them apart.

Kennel Club registrations

The Kennel Club now allows registrations of pedigree litters where planned dual matings have occurred. Since DNA testing has become more readily available these puppies can be easily checked with a cheek swab and the relevant sire recorded in the details for their registration. In the past, permission had to be sought in advance for this type of mating. But it has now been considered acceptable practice.


It is possible to have puppies within the same litter that are sired by two different fathers. Sperm can survive for several days in the bitches reproductive tract. So a couple of matings could lead to the fertilisation of different eggs by different fathers. In some cases, this is obvious (usually when there has been an accidental mismating!). But other times it can be hard to know for sure without DNA testing the puppies.

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