Are Runts Of The Litter More Aggressive?

Runts of the litter are often seen as fragile and helpless. But when it comes to behavior, are runts of the litter more aggressive than their siblings? 

As it turns out, runts of the litter may be more prone to aggression. This article will investigate the reason for this behavior and what it could mean for pet owners.

What Are Runts Of The Litter?

Runts of the litter are usually the smallest and most fragile at birth and have a higher mortality rate than their siblings.

That’s right — unlike most other puppies, runts need extra attention to thrive during the first few weeks of life. They require more frequent feedings at shorter intervals than regular-sized pups do to get enough nutrition for growth. From physical health issues to extra attention needed, these precious pups can be more work than most expect. Yet despite this extra effort, caring for a runt is extremely fulfilling; watching them grow into adulthood is an incredibly rewarding experience that brings joy to all involved.

Why Do Litters Have Runts?

It’s common for litters to have runts, but why does this happen in the first place?

The most common explanation is that the runt simply isn’t getting enough nutrition in the womb and has grown weaker as a result.

Dr. Kustritz emphasizes in the guide, The Dog Breeder’s Guide to Successful Breeding and Health Management, that runts are litters with poor placentation while developing in the womb. 

In the book Canine Reproduction and Whelping: A Dog Breeder’s Guide, the author adds that runts are not really premature puppies; instead, they can be identified as puppies with a less-than-optimal placement within the uterus. Similarly, it is a misconception that large puppies are the result of being born overdue; rather they benefit from optimal placental development.

The presence of runts can also be explained through natural selection. Natural selection is an incredible force that drives evolution and allows species to survive according to their environment. Its main principle is ‘survival of the fittest’, which dictates that animals better suited for their environment will have an advantage over those not as well-adapted. 

This phenomenon explains why runt puppies happen in some cases; they may not be as fit or healthy as their siblings and could struggle to compete for resources (such as milk and food) within their litter, leading them to become weaker than the rest.

Do Litters Always Have Runts?

Do litters always have runts? Contrary to common belief, not every litter has one. Runts may appear in some litters due to genetic or environmental factors, but not all puppies will be small and underdeveloped.

However, in some cases, more than one puppy is born as the smallest compared to its siblings.

Can Runts Of The Litter Grow To Normal Size?

Runts are often regarded as weaker animals who may not reach the same size as the rest of the litter. But can runts ever catch up in size? 

The answer is yes! With proper care, nutrition and lots of love, runts can overcome any initial setbacks they may have had as newborns to grow into healthy adults. They can develop strong muscles and bones that eventually allow them to reach normal size. 

Additionally, they can learn how to compete with their siblings for food and even become more independent within a few weeks or months.

Are Runts Of The Litter More Aggressive?

Now that you have adequate knowledge about runts of the litter let’s investigate their potential for aggression. What is their personality? Are they more aggressive than their littermates?

The idea that smaller animals are fiercer than their bigger counterparts is a widely accepted concept, and this notion is especially true when it comes to runts of the litter. Dog mothers sometimes neglect runts and, as a result, runts develop an aggressive streak. They wage war against larger littermates as they fight for resources to survive. 

In short, the size disadvantage causes them to be more aggressive. This aggression, in turn, offers runts a better chance at survival.

But here’s the good news — even the feistiest runts can grow up confident and well-behaved dogs. With the proper training and guidance, their aggression can easily be modified.

Start by establishing yourself as the leader of the pack. This will give your pup boundaries and structure, so they understand their aggression is unacceptable.

And we always emphasize this: consistency is key when it comes to correcting bad behaviors; set clear expectations for how your pup should behave and consistently reward good behavior with positive reinforcement such as treats or praise.

Every day should include plenty of playtimes and walks so your pup has an outlet for any pent-up energy that could lead to aggressive behavior.

Related Questions

Is it true that the puppy in the middle of the uterus will develop into a runt?

This simply isn’t true! Every puppy is equally as likely to become a runt regardless of their position within the womb.

When determining which pup will become a runt, its successful implantation into the uterus is key, not the placement.

Will the last fertilized egg develop into a runt of the litter?

There is no basis for the claim that the last fertilized egg will develop into a runt of the litter. This is because there are numerous variables to consider when understanding why some pups are born smaller than others, and ‘being the last one in’ isn’t one of them.

One of the most common sources of variation is based on how much nutrition each fetus receives through its mother’s placenta during gestation, which can even differ among siblings.

What are health issues more common in runts of litter?

Undernourishment is one prominent issue that these little guys are particularly prone to. When a runt doesn’t get enough food, its body won’t develop properly, leading to physical and mental deficiencies that can hinder its growth. Physical deficiencies commonly develop in litter runts include dwarfism and cleft palate.

Fading puppy syndrome is another heartbreaking health problem affecting runts of the litter. These puppies are born undersized and face an uphill battle to survive, with their delicate constitutions often leading to premature death within two weeks of birth.

Will the dam reject the runt of the litter?

Usually, a dam will feel overwhelmed by having too many pups to care for at once and can’t provide them all with adequate nourishment; hence she may reject one or two pups. In the case of runts of the litter, they may be at risk of rejection especially since they’re not able to push through and nurse more successfully. 

The rejection of an offspring by its mother is a heartbreaking sight to witness. It’s even more devastating when the one being shunned away from is a tiny, helpless runt. If the mom gives up on one of your pups, you should step in! The pup may require supplemental feeding or even formula if it is having trouble nursing from its mother.

How do you help runts of the litter?

The runt can often have difficulty competing for milk and sustenance, so it’s essential to allow them to get enough nutrition. When feeding the runt, one should consider positioning them closer to their mother’s tail when nursing. This is because the milk will be at its richest here and provide more nourishment for your pet.


Kustritz, M. V. R. (2006). The Dog Breeder’s Guide to Successful Breeding and Health Management E-Book. Elsevier Health Sciences.

Harris, M. S. (2006). Canine Reproduction and Whelping: A Dog Breeder’s Guide.

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