Are Runts of the Litter More Aggressive?

By John Martin - September 14, 2021

Dog litter showing the puppies and the runt

The tiniest dog is often the cutest! However, a question that comes with it is whether this little pup is also the most aggressive. 

Are you concerned about the temperament of your runt? If yes, read on to find the answers you seek about runts of the litter. 

Who Is The Runt Of The Litter?

The tiniest puppy in the litter is generally called the runt. The common assumption is that being the smallest, weakest puppy impacts the dog’s personality, health, and overall development. 

The runt is not always a cause for concern! If the little puppy is within a healthy range of weight for the respective breed and age, you do not need to worry. In these conditions, the puppy will most likely grow at an appropriate rate. 

If a puppy’s weight is unnaturally low at the time of birth, it should spark concerns. Puppies like this give rise to the traditional definition of ‘runt.’ There can be several runts in a single litter in this context. 

Runts with abnormally low weights often struggle to reach critical milestones in their growth and development. Such puppies require intensive care and medical assistance as well. 

Related: Is It Good to Pick the Runt of the Litter?

Why Do Litters Have Runts?

You may be wondering why litters have runts and what causes them to hold the status that they do. A common misconception is that the weaker puppies are born somewhat prematurely due to their later conception. 

Note that it is possible for puppies in the same litter to have different fathers, but all embryos develop together. So, all the fertilized eggs mature at the same pace after catching up during the early pregnancy phase. 

The main reason why runts are born depends upon their innate capacity to grow. The extent of nutrition they received while in the womb is also a factor. 

Congenital disabilities can hinder a puppy’s growth, causing the little one to be born as a runt. An unfavorable location and placement of their placenta is also a factor driving inadequate nutrition. Dr. Kustritz, a veterinary theriogenologist, talks about this in her book ‘The Dog Breeder’s Guide to Successful Breeding and Health Management.’

Do Runts Of The Litter Tend To Be More Aggressive?

Now that you have sufficient background knowledge about runts, let’s dive into the core concern here- are they more aggressive? Typically, people assume that the runt of the litter is bound to be bold. In reality, however, it is not valid.

There is no concrete evidence supporting the belief that the smallest puppy of a litter will display far more aggression than the others. The consensus among veterinarians is that being a runt does not affect the dog’s temperament or disposition.

Despite these factors, you should know that is it quite common for the smallest and weakest puppy in a litter to be aggressive. The small size of the furry baby creates a multitude of challenges for survival.

The suckle reflexes of a runt may be weak in addition to low muscle tonality. It may cause them to lag in their nutrition as newborns or establish a secure spot within the litter. After all, puppy litters are often crowded, and each little one must compete to receive proper attention!

Aggression Offers A Better Chance At Survival  

Runt puppies have a better chance of surviving if they are more aggressive. Their small size and weak frame naturally put them at a disadvantage. The only way for them to compensate for the loss is to adopt a more assertive approach.

A heart-breaking aspect of having a runt in the litter is that the tiny puppy may be at risk of rejection. Dog mothers often reject or abandon babies they deem to be weaklings. The mother chooses to invest her energy and nursing capabilities in puppies with a better probability of surviving.

If a mother rejects a ‘’weakling’’ and chooses not to pay attention to the puppy, the runt will naturally need to develop aggression. In such cases, the most common outcome is an unpleasant one- the runt does not survive. However, with a more aggressive personality, the pup might be able to fight for attention and grow.

Related: Why Do Dogs Bite Each Other’s Necks?

Personality Of An Adult Dog

You should know that the personality and overall aggression of a dog rely upon the upbringing. Most runts will display the typical characteristics of their breed.

Additional traits will take form based on the environment in which the puppy grows. The degree of affection and communication that a puppy receives also dictates the temperament. As a dog experiences significant variations or life changes, there will be reflections in the canine personality.

How To Take Care Of A Runt

It is never easy to nurture a runt. These puppies often have a multitude of health and medical concerns that come with them.

The Health Of Runts

The most common problem that runts face is low birth weight. Each day, puppies should gain approximately 5-10% of their total weight at birth. Runts may have a hard time growing in this manner.

Runts may also suffer from a deficiency of Colostrum. It is a vital type of milk the mother dog produces within twenty-four to forty-eight hours after birth. It contains exceptionally critical elements for the overall development and growth of the immune system of puppies.

The smallest and weakest puppies of the litter often have various congenital problems or genetic abnormalities. They may be prone to infections and parasites, and hypothermia or hyperthermia as well.

The medical concerns that revolve around the runts of the litter are incredibly alarming. Even so, you must not panic and stress out too much. With careful and timely human intervention, it is possible to give the runts a fair chance at survival.

Tips To Nurture A Runt

The first and foremost tip that you must bear in mind is that a runt must remain close and comfortable with the mother. It is essential for warmth. If the mother has rejected the tiny baby, you must immediately find a reliable and consistent source of heat for the puppy.

As you already know, runts are small and weak with low abilities to suckle. An excellent way to ensure they receive the nutrition they need is to allow other puppies to nurse before the runts.

When the milk starts to flow in the mother’s mammary glands, it becomes easier to access- for the weaker ones. You can then move the healthier puppies and place the runt there for easy suckling.

It is critical to monitor the temperature of the runts at all times. Check with your veterinarian and determine the ideal temperature range for your litter.

If you think the runts are not receiving adequate nursing, you can extract milk from the mother dog and use a pet bottle to feed the babies. Puppy milk substitutes are also an option, but make sure you consult with the vet first. You can tube feed runts too.

Puppies generally require assistance from the mother to defecate and urinate properly. A runt may not receive this attention from the mother- you may have to intervene using a lukewarm cotton ball.

You must monitor the runts’ weight daily and visit the vet immediately in case of no development.

Related: How to Stop Your Dog From Eating Rabbit Poop


People commonly question the temperament and personality of runts. The general belief is that these little, weak ones are often the most aggressive. There is no proper and proven evidence to support this claim.

Runts can be more aggressive than other puppies due to their fight for survival in a litter. However, their nature as an adult relies upon their upbringing.