Are animals born in the same litter twins?

Well you could say they’re all fraternal twins. So that would mean they were separate zygotes instead of one splitting zygote. So no they don’t have the same genetic code. However there could be a set of twins in the litter.

Well, I can’t answer for all animals, but I do have experience with laboratory mice. Female mice typically have litter sizes between 6–8 pups. During ovulation, about 6–16 oocytes (eggs) are released. So, most of the pups are probably siblings rather than true monozygotic twins. That said, in laboratory mice strains, they have been inbred for so long that all progeny do share the same genetic code, making them equivalent to identical or monozygotic twins. Does that make sense? I imagine that for cats, dogs, etc., similar things are going on, but typically those animals are not as inbred as lab mice, and so the pups are more like siblings than true twins. I hope that helps.

It’s variable, but most animals that have litters release multiple eggs. Interestingly, some animals can have multiple sperm donors within the same litter. That’s why some dog litters may have remarkably dissimilar puppies (different sizes, different shapes, different hair coats, different ear sets, different colors, and so on).

Like simone54 said they would be considered fraternal twins. But identical would depend on whether they were from the same exact egg then yes they would be considered identical twins.

p.s @ simone54 HI its alex Jacksons g/f lols.