Vets and nursery staff at a US zoo are providing critical care to a baby hippo born six weeks too early.

Cincinnati Zoo says 17-year-old Bibi gave birth on Tuesday to the first Nile hippo born there in 75 years.

The female calf wasn't expected until March.

Cincinnati Zoo Getting the baby up to a healthy weight will be a challenge, says the zoo.

At only 13kg, it's well below the normal range of birth weight of 26-55kg and unable to stand up to nurse.



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The zoo says it is a challenge to get the baby up to an acceptable weight.

Cincinnati Zoo At 13kg, the baby hippo is too weak to stand up to nurse.

Staff members are giving the calf fluids and keeping it moist and warm, says mammals curator Christina Gorsuch.

"Her little system is underdeveloped, and getting her to a healthy weight will be a challenge. Vets and animal staff are doing everything they can to get her through this critical time."

Keepers have collected milk from the mother. Gorsuch says they hope to get the newborn to drink mum's milk and other supplements from a bottle.

"She looks like a normal calf but is very, very small. Her heart and lungs sound good and she is pretty responsive to stimuli, but we aren't sure how developed her muscles and brain are.

"We'll continue to milk Bibi so we can provide these important nutrients to the baby and also stimulate production so she's ready to nurse when the baby is strong enough to be back with mum."

The zoo says vets and animal care staff are providing round-the-clock care for the baby of Bibi and Henry, the 35-year-old father.

The team is not certain how long it will take for the baby to get on her feet.