Do Mom Cats Leave The Runt?

A runt is the smallest or weakest kitten in a litter. Runts tend to be significantly smaller and underdeveloped compared to the other kittens. While runts occur somewhat commonly, with an estimated 20% of litters containing a runt kitten, they face unique challenges that can impact their health and survival.

One of the biggest risks for runt kittens is rejection or lack of care from the mother cat. The mother cat only has so many resources for nursing and caring for kittens. Since runts are smaller and weaker, the mother may choose to focus her efforts on the stronger kittens and neglect the runt.

This article will examine the causes of runt kittens, the potential for rejection by the mother, recommendations for caring for a rejected runt, and the long-term outlook for these special kittens.

Normal Kitten Development

The average litter size for domestic cats ranges from 3 to 5 kittens, though litters can sometimes be larger or smaller (Dutch). Kittens are born weighing between 2.5 and 4 oz on average. They will gain roughly 1 oz per week for the first month, eventually reaching 3-4 lbs at adulthood (Wagwalking).

In the first week after birth, newborn kittens are unable to regulate their own body temperature and rely fully on the mother for warmth and nutrition. Their eyes and ears will open around 10-14 days. Kittens begin to crawl and walk around 3 weeks old. From 4-8 weeks, they will start eating solid food and develop teeth for chewing. Socialization with litter mates teaches them appropriate cat behaviors. By 8 weeks, kittens gain independence from the mother but still rely on her for additional learning.

Causes of Runts

There are several potential causes that can lead to a kitten being born smaller than its littermates, known as a “runt.” Some of the main factors include:

Genetic factors – Certain genetic abnormalities or recessive genes may prevent a kitten from developing properly in the womb and result in a smaller size at birth compared to its siblings. This is due to intrinsic limitations in the genetic makeup of the kitten.

Uterine position – The physical location and space constraints in the uterus can affect nutrient availability. Kittens positioned further away from the placenta or in an overcrowded uterus may have restricted access to nourishment from the mother cat (cite: This leads to impaired fetal development.

Illness or malnutrition of mother – If a mother cat experiences illness, stress, or malnutrition during pregnancy, this can limit the nutrients available for her developing kittens. Kittens affected in utero by restricted nutrition are often born smaller than normal (cite:

Challenges Facing Runts

Runt kittens face several challenges that their larger littermates may not encounter. Three key difficulties runts often experience are difficulty nursing, failure to thrive, and increased health problems.

Due to their small size, runt kittens may have trouble competing with their larger siblings for nursing time. They can get pushed out of the way and fail to get adequate nutrition. Runts may be too weak to nurse for long periods, further inhibiting their ability to get enough milk.

Failure to thrive is common in runts, meaning they fail to gain weight and grow at a normal rate. This stems from challenges nursing and potential underlying health conditions. According to this veterinary resource, runts are prone to problems like hypoglycemia, hypothermia, hypoxia, and diarrhea.

Due to inadequate prenatal development, runts often have more health issues than their littermates. Common problems include heart defects, liver shunts, respiratory distress, and fading kitten syndrome. Runts that survive to adulthood may have lifelong medical problems as a result of their challenging start.

Rejection by Mother

Unfortunately, it’s not uncommon for mother cats to reject or abandon runts of the litter. There are a few key reasons a mother may reject a runt kitten:

Illness – If the runt kitten is sick or weak, the mother may abandon it to focus resources on the stronger kittens that are more likely to survive. Kittens can be born with genetic defects or contract viruses like panleukopenia that cause rejection.

Limited Resources – If food is scarce, a mother cat may abandon the weakest kittens that require the most care and nutrition. With large litters, there may not be enough milk and attention for all the kittens.

Stress – Young, first-time mothers who are anxious or stressed may reject kittens more readily. Nervous mothers may also abandon kittens after too much human handling.

Deformities – Physical deformities, like cleft palates, clubbed feet, or flat-chestedness can provoke rejection. The mother may sense something is wrong.

To encourage acceptance, make sure the mother has a low-stress, comfortable environment with plenty of food. Allow the mother to handle newborns without interference for several weeks after birth. Check for illness in all kittens. Supplement feeding may be needed if the runt is struggling to nurse.

If natural acceptance fails, human intervention through fostering and bottle feeding the runt kitten may be required. Work closely with a veterinarian to give the runt the best chance at health and survival.

Caring for a Rejected Runt

If the mother cat rejects the runt kitten and refuses to nurse it, human intervention is required to help the kitten survive. There are several important aspects of caring for a rejected runt kitten:

Providing supplemental feedings is crucial. The kitten will need a milk replacement formula specifically designed for kittens, such as KMR. Feed the kitten every 2-3 hours using a bottle or syringe (Ochoa). Make sure the kitten is warm before feedings.

Maintaining body temperature is also essential. Since the mother cat is not keeping the runt warm, you’ll need to provide a heating pad or warm towel. Make sure the heating elements are safe and monitor the temperature (TheCatSite).

Monitoring weight daily is important to ensure the kitten is getting proper nutrition. Use a kitchen or small scale to weigh the kitten at the same time each day. Expected weight gain is around 4-8 oz per week (Quora). If weight gain is inadequate, seek veterinary care.

Fostering Healthy Development

Runts often need extra monitoring and care to ensure they develop properly. Their small size makes them vulnerable, so it’s important to encourage eating and monitor weight gain closely.

To get a runt kitten to nurse, try placing them closest to the mother cat’s nipples, or holding the kitten on the nipple to latch on. Gently open the kitten’s mouth and press their face into the nipple if needed. Bottle feeding supplemental kitten milk or formula may also be necessary every 2-3 hours if they are not nursing well (Runt of a Cat Litter: Health Advice from a Vet).

Monitor the kitten’s weight daily with a kitchen or small postal scale. Healthy kittens should gain around 4-8 oz per week. Consult a veterinarian if weight gain is inadequate, as supplements or other interventions may be needed (6 Ways to Identify a Runt Kitten & Help Them Gain Weight).

Veterinary exams are also important to check for health issues like congenital defects, parasites, and low blood sugar. Preventative care like deworming and vaccinations is vital as well.

Long-term Outlook

The long-term outlook for runt kittens can vary greatly depending on the severity of their delayed development and underlying health conditions. However, there are some general trends that can provide insight into what to expect as a runt kitten grows up.

In terms of size, runts that survive past the critical first few weeks often experience catch-up growth and reach normal adult size, though they may remain on the smaller end of the range for their breed. According to one source, “Runts that survive can grow to normal size, but they will usually be smaller than average” (Source). With dedicated care and nutrition, most runts can overcome their initial size disadvantage.

The impact on lifespan is less clear. Some sources suggest average or near-average lifespan is common for runts that thrive past kittenhood. However, severely underdeveloped runts are at higher risk for health problems that could potentially impact longevity down the road. Providing excellent care and veterinary oversight can help maximize lifespan.

In terms of personality and behavior, there are many anecdotal reports of runts exhibiting unique traits like greater independence, intelligence, curiosity, or attachment to their owners. However, these characteristics are not universally guaranteed in runts. According to one expert, “While the runt may sometimes exhibit unique characteristics or behaviors, it’s not a universal rule. Each animal is an individual” (Source). With a healthy upbringing, runts can develop a wide range of normal feline personalities.

When to Be Concerned

It’s normal for some kittens to be smaller or develop a little slower than their littermates, but you should watch for warning signs of failure to thrive or fading kitten syndrome. According to PetMD, signs include “gradually worsening lethargy (lack of energy), lack of appetite, poor suckling reflex, weakness, inability to gain weight, and labored breathing.”

Kittens who show these signs during the first week of life are at the highest risk for fading kitten syndrome. Vetster says if you notice your newborn kitten is not nursing well or seems extremely weak and sleepy, contact your veterinarian right away as fading kitten syndrome can lead to death within days if left untreated.

Some signs like low weight gain may gradually become apparent over weeks. The Kitten Coalition advises closely monitoring daily weight gain, as kittens should gain about 4-8 ounces per week. Consult your vet if weight gain significantly lags behind litter mates or is not steady. With veterinary care, many kittens can recover from failure to thrive.

According to the Kitten Coalition, other reasons to seek prompt veterinary help include if the kitten cries constantly, has difficulty breathing, feels cold to the touch, or is unable to stand or hold up his head. Do not delay if you notice these red flags, as quick treatment greatly improves the kitten’s chances.


In summary, while runts face additional challenges in the early stages of life due to their small size, with proper care they can grow to become healthy, thriving cats. Runts tend to develop slower than their littermates and may be rejected or ignored by the mother cat, requiring supplemental feeding and care from humans. Providing extra warmth, nutrition and stimulation during the critical early weeks can give runts the boost they need to survive and flourish. Though they will likely remain on the smaller side, runts can live long, full lives with their families when their special needs are met. The extra attention and care runt kittens require is well worth the reward of their unique personalities and underdog success stories.

With patience, time and love, even the most fragile runt kitten can blossom into an extraordinary cat. Their fighting spirit and ability to overcome the odds make them truly special pets.

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