It might interest some people to compare the birth weights of some cat breeds. These are the mean birth weights and they come from a study recently published from France. It is published on the Science Direct website. The scientists submitted a questionnaire to French purebred cat breeders from 2016 to 2020. The full study is available online and you can see it by clicking on this link (please note that links to external sites sometimes break).
The table below shows the mean birthweights of the breeds in this limited but useful study. As expected, the birth weights of Maine Coon kittens were the heaviest. Surprisingly the Chartreux kittens were the second heaviest. The Chartreux is not known to be a particularly large cat although perhaps slightly larger than average. It is a French cat breed with an ancient history with a smile of its face. The Norwegian Forest cat is known to be a large cat as is the Siberian but both of them rank considerably lower on kitten birthweights to the Chartreux.
Note: the scientists use two breed names which are non-standard. I believe that ‘British’ means British Shorthair and Scottish Highland means Scottish Fold. Their terminology indicates a lack of knowledge of the breeds.
In fact, the scientists say that the Chartreux has an average adult weight. They think that this “discrepancy” in kitten birthweights may be due to “intra-uterine capacity”. I take this to mean the size of the womb which they suggest is larger in the Chartreux relative to the cats’ size when compared to the other breeds.
The scientists say that the greatest influence on kitten size is the breed of the cat. Another factor is the litter size. And also, the season of birth, the age of the queen and the presence of stillborn in the litter and finally the sex of the kitten.
They confirm that “kitten birthweights increased with the age of the queen (the mother), was higher in males and females and in litters without stillbirth than in litters with at least one stillborn”.
Kittens born in the summer and autumn had a lower birth weight compared to other seasons and birth weight decreased as the number of kittens in the litter increased.
In all, 139 French breeders were involved in providing a large amount of information from 3,547 kittens of 15 breeds.
The kitten birth weight taking the entire study ranged from 41-182 g.
The cat breed with the highest number of litters with at least one stillborn kitten was the Egyptian Mau (32.1% of litters). The next highest was the Sphynx (24% of litters) and in third place was the Maine Coon (23.8% of litters). Despite this negative to birth weight the Maine Coon had the heaviest kittens. The cat breed with the least number of litters with at least one stillborn kitten was the Russian blue. The Chartreux also had a low number of litters with at least one stillborn kitten.
The cat breed with the biggest litter size was a Russian blue at 4.8 kittens per litter. The cat breeds with the smallest litter size was the Abyssinian and Somali at 3.2 kittens per litter.
If this information has whetted your appetite you might like to visit the site and the link is provided above. I have deliberately kept this fairly short and compact because it is quite a technical topic and I know how that, in general, my typical reader does not want to get involved in too much science and detail.
The study: Birth weight in the feline species: Description and factors of variation in a large population of purebred kittens. The lead author: Amélie Mugnier.
Below are some more articles on newborn kittens.