What Is the Runt of the Litter? Vet-Verified Explanation, Health Risks & FAQ

Everyone loves a good underdog story. Witnessing triumph over adversity and obstacles can inspire and encourage us. Fiction, whether on page or screen, is full of such stories. When it comes to the animal world, many of these inspiring underdogs start small—literally—as the runt of the litter. So, what is the runt of the litter? This term means "the smallest and/or the weakest puppy of the litter."

Whether we associate the phrase "runt of the litter," with a triumphant success story or picture a weak, sickly animal destined to live a short life, the truth is that neither of those descriptions is entirely accurate. In this article, we’ll discuss what the runt of the litter is, any health complications they may have, and answer some other frequently asked questions about these tiny, sometimes mighty animals.

What Is the Runt of the Litter?

By definition, a litter is a group of young animals born from their mother at the same time. The "runt of the litter" is a term generally used to describe the smallest or weakest member of that group.

This isn’t a true scientific definition, as some would argue that a small puppy or kitten, for example, isn’t truly a runt unless they’re also weak and sickly. Any litter of animals is likely going to have some variations in size, especially if one parent is significantly larger or smaller.

What Causes the Runt of the Litter?

There are a few possible reasons that an animal might be born a runt. One could be that they’re just genetically wired to be small. Human siblings rarely end up the same size, after all, and animals are no different.

Consider some of the designer dog mixes like a Miniature Labradoodle, for example. Mixing a 60-pound Labrador with a 15-pound Miniature Poodle is bound to result in a litter full of different-sized puppies.

Another reason some animals are born small has to do with the amount of nutrition they receive from their mother in the womb. Some babies have a smaller attachment to the placenta than others, resulting in them receiving less nutrition. Without adequate food, these animals grow more slowly and may be born as the runts of the litter. Runts might also have had less space for their growth and development while in the uterus.

Sadly, some animals are born small because they are also born with a congenital health condition that causes them to be tiny and have trouble growing.

Potential Health Complications for the Runt of the Litter

Just because an animal is born small doesn’t automatically mean that they’re also unhealthy.

As we already discussed, runts can happen because of genetics or nutrition, and neither necessarily predicts health complications. However, animals with a low birth weight can be more at risk for some medical issues and often need human help to survive.

Runts born with birth defects are more at risk for ongoing health complications.

Dangers Just After Birth

During the time that young animals like puppies or kittens are nursing and being raised by their mother, they are at high risk of getting sick or dying, no matter what size they are.

Puppies need cleaning of the placental membranes and some stimulation to take their first breath; otherwise, they will die from hypoxia. Newborn puppies depend on their mother’s care, and this goes beyond just food since a puppy can’t regulate its body temperature.

Puppies are also susceptible to infections, especially those that do not receive passive immunity via their mother’s colostrum, as they don’t have a fully developed immune system to protect them from disease.

All these issues can impact babies who are otherwise healthy and not born with any underlying diseases or conditions. Those that do have other complications, including low birth weight, are even more at risk. A study found that puppies with lower birth weight during the first week of life were more likely to die during that time compared to their larger siblings.

The Extra Risks for a Runt

In many cases, the extra health risks that runts have are directly related to the care and nutrition they get from their mothers.

The smallest animals, especially those in large litters, may have a harder time competing for nipple space with their bigger siblings, especially just after birth. Nursing well for the first 2 days after birth allows babies to receive a special secretion called colostrum from their mother. Healthy mothers pass immune protection and nutrients on to their newborns from these early meals.

If the runt misses out on drinking colostrum, they will be more vulnerable to disease or parasites than their other siblings. In addition, runts often need extra nutrition to make up for what they missed before birth, and if they don’t get it, they’re more at risk of failing to thrive.

Fair or not, some mothers reject their smallest babies. Without their mother’s warmth, milk, and care, these runts usually won’t survive without help.

The combination of all these factors makes runts more at risk for complications, such as fading puppy syndrome. Puppies who suffer these problems may appear normal when they’re born but later become weak, sick, and die within their first 2 weeks of life. Low birth weight is a high-risk factor for these syndromes.

Sometimes Runts Need a Helping Hand

In many cases, the runt of the litter will have their best shot at survival if they get a helping hand from humans. If you’re caring for a newborn litter of puppies, you may find yourself needing to care for a runt.

The first step, if that’s the case, is to work closely with a veterinarian. They are your best resource when it comes to helping you figure out what the runt of the litter needs to survive.

If a runt is otherwise healthy but just small, you’ll need to keep careful track of their weight and eating to make sure they are getting bigger. Use a scale to make sure you can report accurate numbers to a veterinarian.

If the mother rejects the runt, or if they just aren’t growing as they should, a vet may have you take on a bigger role in raising the baby.

You may need to supplement their feeding with puppy formula and keep them clean and warm as if they were truly an orphan. For guidance on how to supplement we suggest booking a consult with an online vet.

Will Runts Always Have Health Problems?

Even though some pet owners may be drawn to choosing the runt of the litter as their own, they may still be concerned that their new pet will always be sickly or have health problems because of their size.

Runts who are small at birth due to lack of space or nutrition but who can grow and gain weight normally often catch up and are the same size as their siblings by the time they’re weaned. These runts generally lead completely normal lives with no health issues.

However, if some underlying health condition is responsible for the runt size of an animal, that’s a different story. These animals may still appear small and even sickly at weaning. Depending on what is the underlying health problem they suffer from, there is a possibility that these runts could continue to have serious and costly health issues.

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Frequently Asked Questions

Here are answers to some common questions and myths regarding the runt of the litter.

Is There a Runt in Every Litter?

Even though this is a commonly used expression, there won’t necessarily be a runt in every litter. For example, some dogs and cats have only a single puppy or kitten at a time. In many cases, littermates are similar in size even when they are multiples.

Will a Runt Always Stay Small?

The answer to this question is the same as to whether a runt will continue to have health issues. It depends on why the baby was a runt in the first place. Animals with birth defects causing them to be small will likely remain small unless the defect can be fixed in some way.

Animals that are small due to lack of space or poor nutrition in the womb, but who are otherwise healthy and able to gain weight consistently, won’t necessarily stay small. Those who are born small thanks to the genetics of their parents could go either way, again depending on their genetics.

Are Runts More Aggressive?

Runts are sometimes believed to be tougher and more aggressive than regular-sized babies, probably because it seems they had to fight harder and overcome more obstacles to survive. While there’s no proof of this particular theory, there is some evidence that runts could have behavioral differences related to their upbringing.

Veterinary professionals have long noted that “bottle babies,” or hand-raised orphan kittens and puppies, often seem to grow up with behavioral issues like clinginess or aggression. Behavioral problems are also often seen in puppies and kittens removed from their mothers earlier than is commonly recommended.

A study from Sweden found that the level of motherly care puppies received appeared to specifically impact their behavior patterns as adults. Given these findings, it stands to reason that runts who may have received less attentive care from their mothers could grow up to display aggression or other behavioral issues.

Is the Runt of the Litter Harder to Train?

There’s no documented reason why training a runt is more challenging than training any other puppy or dog. The ease or difficulty of training a dog has more to do with their breed, temperament, and socialization than whether or not they were the runt of the litter. The experience level of the trainer also plays a role. Patience, positive reinforcement, and plenty of rewards should yield good results in any dog, including runts.

The exception to this could be if your runt has either underlying health problems or behavioral problems such as those we just discussed. These complications could impact the runt’s ability or motivation for learning.

Is It a Bad Idea to Get the Runt of the Litter?

In this article, we’ve addressed many of the common concerns surrounding keeping the runt of the litter as a pet. We’ve learned that some potential problems are grounded in fact while others are more myth than truth. With this knowledge in hand, we know that it’s not automatically a bad idea to get the runt of the litter.

Some breeders, perhaps concerned about possible future health issues, choose to charge less for runt puppies. A knowledgeable pet owner could take advantage of this, again with the awareness that some runts could be dealing with congenital defects.

Balance your knowledge with compassion for your potential new pet, and always make sure you protect your new puppy with pet insurance and get them to the vet as soon as possible for a checkup.

Conclusion

Bringing home any new pet, no matter their size, is both a joyful occasion and the start of a lifelong commitment and responsibility. Choosing the runt of the litter as your new family member may bring with it some additional issues, but don’t assume that will be the case. Deciding which new pet is the best fit for your family involves many other factors than just whether or not they were the runt of the litter.

All pets deserve a loving home, especially one who may have had a bit of a difficult start in life. Don’t decide with your heart alone, but also make sure you’re emotionally and financially prepared if you bring home a runt with possible long-term health complications.

Featured Image Credit: Shift Drive, Shutterstock