A panel of five veterinar, including Dr Utkarsh Shukla from Lucknow Zoo, conducted the autopsy and confirmed that the single-horned rhino died due to infighting.
There were multiple injuries on its body, probably caused by another male rhinoceros, which has been indicated by the presence of foot marks of an adult rhino nearby.
Experts have also ruled out poaching since the horn of the rhino was intact.
Field director Sanjay Pathak said, "We used to call the deceased rhino the fourth son of Narayani and it was possibly killed by an adult rhino. We are yet to identify the one that killed it. It may be injured and in need of treatment."
This is the second rhino death in Dudhwa in the past one year. In February 2019, a 15-year-old rhino was killed by a younger bull in the national park due to infighting.
With the death of the rhino, Dudhwa is now left with 38 rhinos in two enclosures - 34 in Kakraha compartment of Sonaripur range and four in Belraya range of DTR. Of these, 29 are cows and just five are bulls left. Besides, there are four calves in Sonaripur.
The Indian single-horned rhino is listed as 'vulnerable' in the IUCN Red List. Its present population has dwindled to about 2,700 across India and Nepal. Indian rhino is also included in schedule-I of the Wildlife (Protection) Act, 1972.
Rhinos were translocated from Assam to Dudhwa in 1984 and kept in a 27-sq km enclosure in Kakraha in Sonaripur range.
In 2018, Dudhwa successfully launched it second rhino rehabilitation programme by shifting three females and one male rhino from Sonaripur to a 20-km enclosure in DTR's Belraya range.
Most of the rhinos in Dudhwa are offsprings of Bankey, its oldest rhino who died at the age of 50 due to natural causes in December 2016.
A year later, three-year-old Sahdev was killed by three tigers while in February 2019, 15-year-old Bhimsen died due to infighting.
( With inputs from IANS )