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Do Runt Puppies Stay Small? Do They Grow to Full Size?

Runt puppies do not stay small. In fact, when the puppy is fully grown (anywhere between 6-18 months), you’ll have no idea they were the runt. Within 6-8 weeks, runts will begin catching up to their siblings’ weight.

The term “runt” is given to the smallest and weakest puppy in a litter. They are typically below average in size and may experience many difficulties in early life.

Caring for the litter’s runt can be a hard task at first, but within a few weeks, the runt will gain enough size and strength to keep up with its siblings.

As long as the runt survives the first 6-8 weeks, they’ll go on to live a physically healthy adult life. However, some experts claim that runts are more likely to develop behavioral issues later in life.

In this guide, we will go over everything you need to know to make sure the runt grows into a normal and healthy dog.

What Does The Runt Look Like?

Physically, the litter’s runt is well below average in weight compared to the rest of the newborns. They also have a weak bone structure and are especially fragile. Runt animals are not limited to dogs. Any offspring in a litter that is considerably smaller and more fragile is considered a runt.

Runts that have a human taking care of them will typically survive, but if no human is there to take care of a runt, death will likely occur.

Is it Bad to Pick The Runt?

It can be a risk to choose a runt puppy as there are many health concerns, especially at the beginning of their life. However, understanding how to care for the dog responsibly can improve their chances of thriving later in life.

When selecting a puppy, remember that not every litter has a runt. Also, since all the puppies are so small and fragile the first week of life, it may be hard to tell which pup is the runt. However, it should become clear within 2-3 weeks.

Taking Care of The Runt

The first few weeks of a runts life must be handled with caution as they begin to develop their senses and gain strength.

It’s normal for all the puppies in a litter to require special attention to make sure they receive nutrients from the mother and progress at a normal or average rate, but it’s a matter of life and death from the runt of the litter.


The runt puppy may have difficulty suckling and can experience nutritional deficiencies. This will have a negative impact on their immune systems and growth, so it is important they are being encouraged to drink milk.

If the runt of the litter is unable to drink milk from their mother, human intervention is required.

Feeding The Runt of the Litter

First, since this puppy likely has a weak immune system, it is important to handle them with extra care. Sanitary practices like clean bottles and wearing gloves when handling them can save their lives during this critical window.

If a runt puppy fails to get the nutrients it needs, you can put on gloves and squeeze some milk from the mother into a bottle, then bottle feed the puppy. Milk flows much easier from a bottle than it does from the mother.

If the puppy is still unable to drink from the bottle, you’ll need to begin syringe feeding.

Using Puppy Milk Replacer

If possible, you’ll want to use the mother’s milk on the runt for the first three weeks. After three weeks, it’s okay to wean them off of their mother’s milk.

At this point, they can be introduced to milk substitutes (such as puppy milk replacer), and around 6-8 weeks, they can begin eating normal puppy food.

The Importance of Tracking Weight

It’s considered best practice to weigh each newborn pup. This helps to determine which puppy might be the runt.

Tracking the weight each day will also show you which puppies are struggling to develop and may need special attention.

A lot of growth takes place in those first few weeks, and a lack of weight gain can indicate that the runt needs human intervention.

If the runt is still unable to gain weight, there may be a more serious health issue going on. Be sure to schedule an appointment with the vet as soon as possible.

The Importance of Keeping a Runt Warm

If possible, a runt should stay close to their mother. Not only will this encourage them to drink her milk, but it will help keep them warm.

Runts are prone to hypothermia. In the wild, if a run doesn’t die from lack of nutrition, there’s a good chance they’ll die from hypothermia.

It takes the runt several weeks before they can regulate their body temperature on their own. Until then, it’s a good idea to keep them by their mother for warmth.

If this isn’t possible, you’ll need to take the necessary steps to keep the puppy warm.

How to Warm a Runt

Unfortunately, runt puppies are sometimes rejected by their mother. This practice is thought to be based on the instinct that she is trying to take care of the puppies she knows will survive.

This presents a major challenge when trying to keep the runt warm. If the mother has rejected the runt, human intervention is (once again) required.

The best way to keep a runt warm is to get a heating pad designed for dogs and let the runt sleep on the heating pad. However, make sure you place a few towels on top of the pad. The last thing you want is to overheat the pup.

Do Runt Puppies Stay Small?

Typically, if a runt can make it past the six to eight week threshold, they will survive and grow to be full size.

There are exceptions to this, as mentioned before. Some runts have congenital disabilities and cannot develop in the same way the rest of the puppies do.

A runt puppy may experience challenges initially, but with help, they can fight through these hurdles and live a full life.

Adopting the litter’s runt may bring about a set of difficulties since there are potential health problems still at play. But they can be raised and trained in the same way any other dog would as long as they receive the proper care.

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