Can animals give birth to twins?

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Can animals give birth to twins? – Mia C., age 10

Ask any parent – welcoming a new baby to the family is exciting, but it comes with a lot of work. And when the new addition is a pair of babies – twins – parents really have their work cut out for them.

For many animal species it’s the norm to have multiple babies at once. A litter of piglets can be as many as 11 or more!

A mother pig lying on hay in a barn surrounded by multiple piglets

Pigs are one species that gives birth to large litters.
Arthur Dries/DigitalVision via Getty Images

We are faculty members at Mississippi State University College of Veterinary Medicine. We’ve been present for the births of many puppies and kittens over the years – and the animal moms almost always deliver multiples.

But are all those animal siblings who share the same birthday twins?

Twins are two peas in a pod

Twins are defined as two offspring from the same pregnancy.

They can be identical, which means a single sperm fertilized a single egg that divided into two separate cells that went on to develop into two identical babies. They share the same DNA, and that’s why the two twins are essentially indistinguishable from each other.

Twins can also be fraternal. That’s the outcome when two separate eggs are fertilized individually at the same time. Each twin has its own set of genes from the mother and the father. One can be male and one can be female. Fraternal twins are basically as similar as any set of siblings.

diagram of two sperm fertilizing two eggs yielding two embryos, and one sperm fertilizing one egg that divides into two separate embryos

Fraternal twins originate in two eggs fertilized separately, while identical twins originate in a single fertilized egg that divides to create two embryos.
Veronika Zakharova/Science Photo Library via Getty Images

Approximately 3% of human pregnancies in the United States produce twins. Most of those are fraternal – approximately one out of every three pairs of twins is identical.

Multiple babies from one animal mom

Each kind of animal has its own standard number of offspring per birth. People tend to know the most about domesticated species that are kept as pets or farm animals.

One study that surveyed the size of over 10,000 litters among purebred dogs found that the average number of puppies varied by the size of the dog breed. Miniature breed dogs – like chihuahuas and toy poodles, generally weighing less than 10 pounds (4.5 kilograms) – averaged 3.5 puppies per litter. Giant breed dogs – like mastiffs and Great Danes, typically over 100 pounds (45 kilograms) – averaged more than seven puppies per litter.

When a litter of dogs, for instance, consists of only two offspring, people tend to refer to the two puppies as twins. Twins are the most common pregnancy outcome in goats, though mom goats can give birth to a single-born kid or larger…

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