Why is there often a runt in a litter of puppies?

When a bitch has a litter of more than around three pups (or sometimes even with very small litters too) there will often be a pup that is smaller, more fragile and slower to develop than the other pups, and that may also be more prone to being frailer or unhealthy-this is what we call the runt of the litter.

While not every litter has a runt, the larger the litter size, the higher the chances are of their being one, and many or even most medium to large litters will have an obvious runt, which can be identified soon after birth in most cases. What it means to be the runt can be vary variable too-some runts will be much smaller than the other pups, develop much more slowly, always be the last to feed, and be much more prone to ill health or inherited health problems-while others may simply be a touch smaller at birth, and catch up quickly.

Just because a pup is born the runt doesn’t mean that they will not grow up to be a normal, robust and healthy dog-and often, once a litter is fully grown, it will be difficult or even impossible to pick the runt out from their siblings. However, if your litter contains a runt or if you are considering buying or adopting the runt from a litter, it is important to learn about what being the runt means for the pup in question, at least until they are grown-and how to care for them properly to help them to thrive.

If you have ever wondered why there is often a runt in a litter of puppies, and what determines which pup will be the runt, in this article we will answer these questions. Read on to learn more.

Breeding factors that can contribute to producing a runt

Having a runt of the litter is common, and runts crop up across all dog breeds, and is not a breed-specific issue. However, there are certain factors that can contribute to making a runt, and certain known elements that make it more likely for a litter to contain one.

Dog breeds and breed lines that commonly have large litters are more likely to produce a runt, as the larger the litter is, the more thinly spread the dam’s resources will be, even before the litter is born. Larger dog breeds tend to have larger litters as standard, but for tiny dog breeds like the Chihuahua, producing large litters is less common, and so a large litter from a small dog is more likely to produce a runt.

Additionally, any breeding pair that are not in optimum health and condition when bred have a higher chance of producing a weaker litter, particularly if the bitch is very young or old, or not in optimum condition. A weaker litter increases the chances of there being a runt, and of the runt itself being smaller and weaker than it would otherwise be.

Development prior to birth

If a pup is going to be the runt of the litter, this is determined prior to their birth, and takes place while they are still growing and developing in the womb. Usually, which pup will be the runt is actually determined by their position in the womb in relation to their littermates-the uterus is Y-shaped, and the pup that develops in the midpoint of the “Y” rather than at the ends and sides is the most likely to be the runt, because they are the last to receive nutrients via the bitch’s blood supply, due to being the furthest away.

Delivery

Where the runt falls in the delivery order can be very variable, but they will often be the last to be born, sometimes surprising breeders who thought that the dam had delivered all of her pups with a final late arrival!

The runt is likely to be identifiable as being smaller than the other pups-although with very small dog breeds, it can be hard to tell until you have weighed all of the pups-so if you do find that one pup’s weight is rather under that of the rest of the litter, pay them special attention because they may be the runt.

The pup’s first few weeks

Because runts tend to be smaller and weaker than their littermates, they may not do well in competition for milk and the dam’s other resources, always being last to feed or not being able to get to a teat.

While monitoring the runt (and of course, the rest of the litter too) for growth and development and keeping a careful eye out for any problems, you will also need to ensure that the runt gets enough to eat, which may mean placing them on a teat and/or moving other pups that have fed or that push the runt out of the way so that the runt can get enough nutrients.

The dam’s colostrum and milk are vital to helping the runt to grow and develop normally and catch up with the rest of the litter’s progress, as well as to help to build their immune system and give them the best chance of starting life healthy and well.