A zoo in Ohio is celebrating the 'miracle' birth of three rare Amur tiger cubs after it was feared their mother's biological clock had stopped ticking. Keepers at the Columbus Zoo say ten-year-old Irisa had mated before but never conceived. However, this spring it was found the female cat was pregnant - with triplets. While the birth on Tuesday morning went smoothly, Irisa failed to show any maternal care so her offspring are currently being hand-reared in an incubator. Scroll down for video . Open wide: A zoo in Ohio is celebrating the 'miracle' birth of three rare Amur tiger cubs after it was feared their mother's biological clock had stopped ticking . Bundle of joy: Keepers at the Columbus Zoo say ten-year-old Irisa had bred before but never conceived - however, this spring it was found the female cat was pregnant - with triplets . 'We are always cautiously optimistic about the survival of fragile newborns,' said Columbus Zoo president Tom Stalf. 'But the cubs seem to be thriving under the 24-hour care provided by our animal specialists and veterinarians.' Video footage shows the newborn siblings writhing around and napping. The baby cats currently weigh a healthy 2.5lbs but they're set to grow to a heftier 650lbs. Their eyes are also closed but should open over the coming days. In safe hands: While the birth on Tuesday morning went smoothly, Irisa failed to show any maternal care so her offspring are currently being hand-reared in an incubator . Taking it easy: Video footage shows the newborn siblings writhing around and napping . It is unknown when they will go on display to the public and how keepers will go about naming them. These are the first cubs for ten-year-old female, Irisa, although the Zoo team and the Tiger Species Survival Plan (SSP) had hoped for years she would reproduce and pass on her valuable genes. This is the third litter sired by 11-year-old, Foli, since 2012. Gestation for tigers is about three-and-a-half months which means the cubs were conceived just weeks before Foli left for another facility in Kansas on February 25. He has been retired from breeding. Tiny tots: They currently weigh 2.5lbs but are set to grow to a heftier 650lbs . Growing pains: Their eyes are also closed but should open over the coming days . Bright futures: It is unknown when they will go on display and how keepers will go about naming them . A new male tiger, Jupiter, arrived at the Columbus Zoo on March 19. Jupiter was born at the Moscow Zoo in 2007 and came to the Columbus Zoo from the Dvur Kralove Zoo in the Czech Republic. Both males were moved at the recommendation of the Species Survival Plan in an effort to maintain a sustainable population of tigers in human care. With the addition of the three cubs there are currently ten Amur tigers at the Columbus Zoo including four cubs born in 2013 and their mother, Mara.
Keepers at the Columbus Zoo say ten-year-old Irisa had bred before but never conceived.
However, this spring it was found the female cat was pregnant.
While the birth on Tuesday  went smoothly, Irisa failed to show any maternal care so her offspring are being hand-reared in an incubator.
They currently weigh 2.5lbs but are set to grow to a heftier 650lbs.