Runt of a Cat Litter: Health Advice from a Vet

Is one of your kittens smaller than the others? You may have a runt of a cat litter. We consulted with one of our veterinarians at Cat World, Dr. Sara Ochoa (Doctor in Veterinary Medicine), to give you the best information on runts and how to care for them.

What is a runt of a cat litter?

Have you ever read or seen Charlotte’s Web? Or Clifford the Big Red Dog? Wilbur and Clifford were runts of the litter. A runt is a member of a litter who is significantly smaller or weaker than the others. When Wilbur and Clifford were born, his mother wouldn’t feed him, but he was bottle-fed by the humans who took him in. He grew big and strong after this. While this is a commonly known example, runts can happen in any litter of animals born with multiple births. This includes cats.

runt with sibling kittens

What causes the runt of the litter?

There is nothing specific that causes the runt of the litter. It’s simply lousy luck while developing in utero. A run is caused by a lack of nutrients in the womb compared to its siblings. When those runts are born, it can be hard to feed due to medical defects or weakness compared to their siblings. When there are eight kittens and six spots to eat, someone doesn’t eat. And it’s often the runt who suffers unless someone intervenes.

Does every cat litter have a runt?

Not every cat litter has a runt. While all animals in a litter will vary in size, the smallest is not always a “runt” if it’s healthy and close to the size of its littermates. Runts are born underdeveloped and often look several weeks younger than their siblings.

What you need to know about runt kittens

If you think you have a runt, don’t panic. Luckily, with today’s veterinarian advances and dedication, runts are more likely to survive than in the wild.

runt of the litter kitten on grass

How to tell if I have a runt kitten?

  • Size: As mentioned above, one of the signs of a runt is small size. When they are adults, they are typically smaller than other cats the same age. Because runts often don’t get vital nutrients during and after pregnancy, their growth is stunted.
  • Suckle: If a kitten can’t suckle, it’s a large sign. Sometimes kittens have medical issues such as a cleft palate which prevents them from latching. Other times, they have difficulty competing with the more robust kittens for the nutrients.
  • Weakness: Kittens don’t move much in the first few weeks. But as they grow, kittens play and wrestle with each other. After about a month, kittens are underfoot exploring! But runts aren’t as strong as their littermates. You may not see them exploring or playing with the others.
  • Fading Kitten Syndrome: Fading sitten syndrome is a kitten’s failure to thrive between birth and weaning from their mother. While not only runts can have this illness, it’s also more common due to their predisposition to weakness and size issues. Kittens who don’t meet developmental milestones may be experiencing this illness. Others include constant distress noises, lack of appetite, not gaining weight, labored breathing, etc. If you believe a kitten may be experiencing this, get them to a veterinarian.

Does a runt kitten stay small?

Small size as a kitten may indicate a runt and is often the most outward sign. The size of an adult cat is hard to predict. Multiple factors include breed, gender, nutrients, and illness. Litter runts who survive six to eight weeks are likely to grow close to full size. Your veterinarian typically will evaluate the weight and condition of your cat during each check-up. If you have any concerns, don’t hesitate to bring them up.

What is the life expectancy of a runt cat?

An indoor cat’s life expectancy is 10 to 15 years. Cats become part of our family, and it always hurts to lose a family member. The obvious next question is whether being a runt will affect life expectancy? No studies indicate that being a runt affects your cat’s life expectancy.

When a cat has a large litter of kittens, and there is an obvious runt, what are the chances of its survival?

It’s hard to predict the chance of survival for the runt of a litter due to the lack of studies dedicated to it. What is known is this. If a runt is born in the wild to a large litter, its chance of survival is next to zero. If a runt is born domestically and humans take necessary actions, their chances increase. But it’s impossible to give percentages due to the unique nature of each case. Follow the instructions of your veterinarian for the best possible results.

How will the runt kitten interact with siblings? Any risks?

As stated above, runt kittens often do not play or wrestle with their siblings. They are kept away from the nutrients due to weakness; runts cannot fight for dominance for milk. As they grow, runts will hopefully interact positively with their siblings, but it’s hard to know.

There are always risks for kitten littermates. Littermates are how kittens learn to interact with other cats: how to play, wrestle, and how much is too much. Runts are smaller, so playtime with littermates should be supervised to prevent injury.

Potential health issues with the runt of the litter

runt kitten

We have consulted with one of our veterinarians at Cat World – Dr. Sara Ochoa. Dr. Ochoa is also a veterinarian at Whitehouse Veterinary Hospital in Texas. She says, “Runts of the litter may not be fully developed and have health issues. These kittens also have issues getting proper nutrition. Sometimes, the runts of the litter do not survive due to these issues.”

Risks at birth or after birth

Runts are more likely to be born with developmental issues due to a lack of blood supply and nutrients in the womb. Kittens can also acquire health issues after birth due to a poor immune system and small stature.

  • Parasites: Mothers can pass fleas and worms to their kittens through milk or contact.
  • Viral Infections: Due to the close contact in the early weeks, viral infections spread quickly. This is why issues like FIV, FELV, and Herpes viruses spread quickly through the litter.
  • Inheritable Diseases: Mothers with certain diseases can pass through genetics to kittens. This can range from deafness to heart disease.
  • In-Utero Defects: Kittens can develop defects while growing in utero, affecting their ability to feed and grow. Dr. Ochoa advises, “Many runt kittens have not had their lungs fully developed. These kittens often need supplemented milk to help maintain a proper weight and continue to develop.”

Is my runt kitten’s life at risk? Signs of a kitten dying

small kitten drinking milk off the bottle

While no one wants to think about it, runts can always pass away. They are prone to health issues, making it harder to gain weight and grow. It’s distressing to consider, but here are some signs of a kitten dying.

  • Lethargy
  • Lack of interest in nursing
  • Sleeping separately from the litter
  • Whining
  • Failure to gain weight

How to care for a runt kitten

dog caring for runt kitten

Dr. Ochoa weighs in on caring for runts: “It is best to weigh them every day. Many do not gain weight as they should. If they don’t gain weight, you will need to supplement milk. As long as they gain weight, they are growing and developing.”

Overall, there are five requirements for raising underage kittens. As runts often cannot gain nutrients from the mother directly, humans have to step in and provide what a mother does typically.

  • Warmth: Kittens under four weeks cannot regulate their body warmth. If the kitten is accepted by the litter and the mother but cannot gain enough nutrients, you may not have to intervene here. Cats and kittens cuddle for warmth, especially underage kittens. If you notice this, it should be good.
  • Nutrition: This is the most significant risk factor for runts. Daily weight gain indicates the kitten is meeting their nutritional needs. If not, you will have to bottle feed. Kittens less than two weeks old should eat at least every 2 hours. Kittens 2 to 4 weeks should eat every 3 to 4 hours. For additional guidance for bottle feeding, see here.
  • Clean: If the mother has abandoned the kitten, you will have to stimulate urination and defecation. Kittens need to be stimulated until about three weeks. Do it before and after each feeding. Ensure they are urinating every time and should defecate at least once daily.
  • Socialization: Kittens learn to socialize from their interactions with humans and other kittens. When the runt is rejected, we must step in to provide this. As much as it’s a sacrifice, you must play with the kitten to ensure socialization. This is key, especially between weeks 4 and 12.
  • Disease: The most important is watching for illness or disease. Like an undersized human baby, runts are more likely to be ill. If you have concerns regarding the health of the runt, seek care from a veterinarian.

The personality of the runt of the cat litter

The personality of an adult cat is significantly influenced by its experience as a kitten. Kittens who are cuddled are more likely to enjoy petting as an adult. Kittens with negative dog experiences are less likely to get along with dogs. Runts don’t have any particular personality traits.

What can happen is runts are often hand-reared, which means lots of human interaction. If a kitten bonds closely with  a human, they are more likely to have a close relationship.

Is it a bad thing to get the runt of the litter?

No, it’s not a bad thing to get the runt of the litter. If a runt makes it 6 to 8 weeks, most likely, they will continue to survive. Runts are more likely to develop illnesses and defects as a kitten, but many healthy kittens can develop those too. As always, consider all factors before adopting a kitten. Kitten illnesses are a consideration when adopting.

It can be concerning to know runt kittens are prone to health problems in kittenhood. However, “as long as they get proper nutrition, they will start to grow and develop,” claims Dr. Ochoa. “These kittens will reach the same size as their siblings. They can live just as long and usually don’t have any long-term health issues.”

Do people still adopt the cat litter runt?

Many people adopt the runt of the litter. Due to the close bond from hand-rearing, runts are often adopted by the human who raised them. When we look at babies, we coo at small proportions; there’s an instinct to protect them. This is an advantage when it comes to adoption for runts. Runts’ small size is a risk at birth but an appeal to potential adopters.

Can there be more than just one runt in a single litter?

There cannot be more than one true runt in a single litter. Mothers have a Y-shaped uterus. Kittens growing in the center of the Y get the least amount of food and have a more significant chance of becoming runts. Those closest to the mother’s blood supply get the most nourishment.

Great names for the runt of the litter cat

As size is the most prevalent adjective of a runt, it’s often what we use to name them. Pet parents can spend days or weeks debating what name is suitable for the new addition to their family. It’s a big decision—you’ll be saying it for the next 10 to 15 years.

Here are some great suggestions and their meanings:

  • Adena– delicate, small
  • Bec– small
  • Carlie– small champion
  • Finn– small blond soldier
  • Keegan– small and fiery, bold flame
  • Pebbles– small rocks
  • Posy– small flower
  • Shannon– small but wise
  • Whitley– a small field
  • Wren– a small bird


  • Dr Sara Ochoa, DVM

    Dr. Ochoa is a veterinarian for Whitehouse Veterinary Hospital in Whitehouse, Texas.

  • Elizabeth Lasley

    Elizabeth is an animal lover who is owned by three cats: Vivan, Burr, and Puck. Her passion for writing started in the 9th grade when she began writing her novel. She hasn't stopped since.