Hippopotamus Puppy with her then newborn Shanti in 2006, a year after she had arrived at Alipore zoo under an exchange programme with Mumbai zoo

Alipore zoo lost a 29-year-old female hippopotamus named Puppy in a freak incident late on Tuesday that nobody knew about until her keeper found the 3,000-kg mammal floating sideways in her moat on Wednesday morning.

A solid object getting stuck in the hippo’s intestine is suspected to be the cause of death.

“According to the post-mortem report, the animal’s death occurred sometime late on Tuesday. An impaction of the small intestine appears to be the cause. More tests will be conducted to determine what caused the impaction,” Kanai Lal Ghosh, director of Alipore zoo, told Metro.

Impaction of the intestine can be caused by a solid food particle, mud or any other object consumed by an animal, according to a veterinarian in the animal husbandry department.

“It is not rare amongst large herbivores that consume leaves and grass in large quantities. Inactivity over a prolonged period or a change in diet are other possible reasons,” he said.

Puppy, born in 1986, had come to Alipore zoo in 2005 under an exchange programme with Mumbai zoo and gave birth to Shanti the next year. Mother and daughter have since been among the zoo’s attractions along with the other two hippos, though none among the quartet was included in the zoo’s maiden adopt-an-animal programme earlier this month.

Puppy’s keeper Bimal said the hippo had shown no noticeable abnormality throughout Tuesday.

The wall demolished to move 3,000-kg Puppy for post-mortem. Picture by Sanjoy Ghosh

Puppy’s “calm nature and general lack of aggression” would have made it even harder for Bimal and the other zoo keepers to find out if she was in any kind of discomfort.

“A hippopotamus spends close to 18 hours in water. So to detect any dullness or any other abnormality in behaviour is very difficult,” said veterinarian D.N. Banerjee of Alipore zoo.

Normally, small portions of a hippo’s barrel-shaped torso and large mouth are visible above the water. On Wednesday morning, keeper Bimal saw Puppy floating sideways and instantly knew that something was horribly wrong.

The post-mortem was conducted in the hippo enclosure itself to avoid moving the 3,000kg animal to the zoo hospital across the road.

A crane was brought to lift Puppy from the ditch and a wall was demolished to move her to the covered section of the enclosure for the post-mortem around 2pm.

Puppy’s death has again brought into sharp focus the poorly maintained zoo environment. “The water in which Puppy spent most of her life has never been cleaned. The enclosure is dirty, too,” said Rakesh Singh, president of the Alipore Zoological Employees’ Union.

Alipore zoo has had its share of flak over unnatural deaths of animals but improvement in veterinary care over the past few years has made a difference.

The last of the four kangaroos that had been brought from the Czech Republic died in August last year and no unnatural death had since been reported in the zoo until Puppy was found floating lifeless on Wednesday.

Daughter Shanti was a forlorn figure on Wednesday, staying put in a corner of the moat for most of the day. Mother and daughter were inseparable for as long as they had been together in the enclosure.

“Thankfully, Shanti has been having her food,” her keeper said.

Puppy’s diet had included several dozens of bananas, sweet potatoes, green leaves, grass and hay.

No zoo official would hazard a guess about what got fatally stuck in her intestine.