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Why is one kitten in my litter weighing less than its siblings?

Updated on September 23rd, 2025

Pet's info: Cat | Domestic Shorthair | Female | unspayed | 1 year and 5 months old

Kiara gave birth to a litter of five Sunday morning and unfortunately one of the little babies passed away. I've weighed the rest of them and these are the weights. Kitten 1- 109g Kitten 2-94g Kitten 3-110g Kitten 4-112g My concern is for kitten 2 as it weighs considerably less then the other ones. It feeds well. Could you shred some light as to why it doesn't weigh as much as the others.

3 Answers

Most Helpful Answer

Dr. Dayna, DVM, CVA

Answered By Dr. Dayna, DVM, CVA

Veterinarian, Certified Veterinary Acupuncturist

Published on March 14th, 2018

Hi there again, cats can breed multiple times to multiple males during their heat. So it is possible that the smaller
Kitten has a different DNA makeup and it is also possible that it may be a day or 2 younger than the others if if was from a later breeding. Of course there is always a possibility that something may be more concerning with the kitten such as an internal birth defect. Keep weighing them to make sure they are all gaining weight daily. If you have any concerns please have them examined by your veterinarian. Best of luck and thank you for using Pet Coach.
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Related Answers from Veterinarians

  • Answered By Dr. Dayna, DVM, CVA

    Veterinarian, Certified Veterinary Acupuncturist

    Published on March 13th, 2018

    Good job weighing them! I wouldn’t be too concerned about the weight difference. However, I would continue to weigh them twice a day. Each kitten should be gaining weight every day. If the weight doesn’t increase daily then that is a red flag that something is wrong. At that time supplemental feedings with KMR after it nurses is appropriate. Also having it examined by a veterinarian to make sure there is no cleft palate or heart murmur etc. Best of luck and have fun with those kitties! Thank you for using Pet Coach.

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    1Pet Parents found this answer helpful

  • Answered By Maria DVM

    Veterinarian

    Published on April 20th, 2019

    I wouldn't worry too much unless that kitten looks frail, sick or not well for some reason. I would not force anymore milk onto them and let them drink what they would like. If the kitten isn't doing well then I highly recommend taking them to a veterinarian as soon as you notice that. Thank you for using Petco Pet Education Center, formerly Petcoach.

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    1Pet Parents found this answer helpful

Smart Picks for Smart Questions

Vet Q & A
Why is one kitten in my litter so much smaller and weaker than its siblings?
It’s hard to know why one kitten is so much smaller than the other. It could be normal, it could be that the kitten suffers from parasites or it is possible that the kitten has a congenital abnormality that is causing a failure to thrive. I recommend to have the kittens are checked for worms and coccidia. The veterinarian may also recommend to deworm them to be on the safe side. The best you can do for the small kitten is to have it examined and see if the doctor thinks it is normal or has a health issue. I hope this helps.
Updated on September 23rd, 2025
Vet Q & A
Why is my kitten not growing or gaining weight unlike siblings?
Hi and thanks for posting on Petco Pet Education Center, formerly Petcoach! Lack of growth and failure to gain weight in a kitten can be due to a number of medical causes- viral or bacterial infections and parasitic infections could be potential causes among others. I would recommend having the kitten seen by a veterinarian for an exam and assessment. You may wish to bring a fresh fecal sample to the vet appointment in case your vet wants to test the kitten's stool. I hope this helps and thanks for using Petco Pet Education Center, formerly Petcoach!
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New Pet
My newborn kittens are different sizes. Is the small one getting enough milk?
A newborn kitten usually weighs about 100g. So the small one is a normal weight and the big one is really big. They will gain about 100g/week. So if your smaller kitten gains about that much/week, it is getting enough milk. Mama has more nipples, so it will likely be able to drink while the other is suckling somewhere else. Just observe them. For now I would not worry.
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My cat had kittens. Is the small one a runt? What care is needed?
The best thing you can do is to weigh her twice daily to make sure she's growing appropriately. Kittens should gain 10% of their birth weight per week, or if you don't know the birth weight you should make sure the kitten is gaining weight each day and not losing weight. If she is not gaining weight it would be a good idea to see a vet for an exam and potentially to supplement with bottle feeding.
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My cat is small, not the runt. Why is she tiny compared to siblings?
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Why are my kittens refusing the bottle and gaining less weight?
As long as they are all continuing to gain weight steadily you can continue to monitor them for now. It is normal to see some variation among littermates. However if they're smaller kittens show other signs are not thriving such as decreased play behavior, being isolated from the other kittens, or they stop gaining weight then you need to try to supplement formula again.
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Why is my 15-month-old cat so small and underweight at 3.5 lbs?
Some cats are naturally smaller than others, and it's due to their genetics. I have a Persian male cat who is quite small as well, and he doesn't weigh very much. It could also be due to a deficiency with digesting nutrients, and it would be recommended to have a health check done on Allee to be sure she is healthy.
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