Irish Wolfhound gives birth to first scientifically proven identical twin puppies

A beautiful grey Irish Wolfhound thrilled scientists in 2014 when she gave birth to the first scientifically proven identical twin dogs – named Romulus and Cullen – via Caesarean section, finally proving to scientists through genetic analysis that dogs can host monozygotic twins born from the same egg.

Although there have been anecdotes of dogs birthing identical twins for years, this was the first time scientists could look to a confirmed case. While births of identical twins in humans are relatively common – about 1 in 250 – in other species it is incredibly rare.

Of the estimated half a billion dogs on the planet, these lucky puppies are the first reported pair.

Kurt de Cramer, a South African veterinarian, helped deliver the puppies at South Africa's Rant en Dal Animal Hospital in Mogale City, when the owner brought her into the clinic in distress. 

While there, he found the two healthy dogs attached via umbilical cords to the same placenta, something he had never seen before in decades of practice.

After safely delivering Romulus and Cullen’s five other siblings – each surrounded in its own placenta, like usual for dogs – de Cramer was able to examine the twins in more detail. Although they did look remarkably similar, albeit with some different white markings, it wasn’t until the blood samples came back that the vet could confirm the puppies were identical twins born from the splitting of a single fertilized egg.

“The twins looked very similar,” said Carolynne Joone of James Cook University, one of the researchers who looked at the samples. “But pups from the same litter often do, [and] there were small differences in the white markings on their paws, chests and the tips of their tails. I wasn’t sure they were monozygotic [identical] at all initially.”

Nevertheless, scientists tested the samples, because not all identical twins look exactly alike – just like human twins, subtle environmental cues can impact how identical genes get expressed.

And how about that! The tests proved that the twins were born from the splitting of a single fertilized egg – research De Cramer published in the journal Reproduction in Domestic Animals.

There, scientists report that although twinning is rare in the animal kingdom – except for the nine-banded armadillo, which for some reason only gives birth to monozygotic quadruplets – these miraculous Irish Wolfhound puppies prove it is possible.

The reason these cases are often underreported is because they are often fatal – for twin embryos attached to one placenta, the animal womb is a stressful place, and one or both of them often do not receive enough oxygen, causing the animals to die.

Dogs are also often known to gobble up the placenta after they give birth, so unprepared witnesses might not always check if there is one more placenta than there is puppy.

Still, it's likely more identical twin puppies might exist.

“It has taken so long for us to find a monozygotic pair, so they are probably rare,” said Joone. “But so many of them will have been born naturally and blissfully unaware.”

Header image of generic Irish Wolfhound puppies: Anna Dudkova / Unsplash