It is alleged that many of the farmers are actually selling the animals, rare or otherwise, for Vietnamese dinner tables and medicinal purposes.
There are an estimated 4,000 farms breeding wild, rare and endangered animals throughout Viet Nam.
Colonel Tran Trong Binh, director of the Department of Environment's Crime Prevention Police Department, said last month Cau Giay District Police raided an illegal wild-animal slaughter house in My Dinh Commune in Ha Noi's Nam Tu Liem District.
A Vietnam News Agency correspondent said that when the police arrived, dozens of porcupines had just been killed and their hearts, livers and bowels were heaped up on the ground.
Pangolins, porcupines and civets were kept in narrow cages while many others were in tiny cages ready to take to restaurants.
Viet Nam Wildlife Conservation Society recently joined hands with the Department of Forest Management to check on 78 wild-animal breeding farms across the country.
The survey showed that the farms were raising 22 different species, 12 of them threatened at the national level and six of them threatened at the global level.
This means that six of the animal species were not protected and therefore, presumably for legal sale.
However, a disturbing trend was that more than 40 per cent of the farms regularly take wild animals from the wild to use as breeding animals. Statistics from the Viet Nam Association for Conservation of Nature and Environment (VACNE) show that 4,000 enterprises in the country are registered to raise wild animals.
Professor Dang Huy Huynh, deputy chairman of VACNE, said that the enterprises also served domestic and export demands, helped preserve genes and reduced poverty and illegal hunting.
However, he said, many rare wild animals were illegally caught in the wild and taken to the farms to "legalise" their origin.
He blamed slack management by authorities for this. "I have never known a management office to declare a species being bred as endangered," he said.
The country also did not have detailed technological guidance on the size of cages and farms and regulations for breeding the animals.
Huynh said that to reduce violations, police and environmental agencies should check all 4,000 enterprises.
Strict penalties should be given to enterprise owners who could not show legal papers relating to the origin of all their animals.
Huynh also said detailed regulations on breeding wild animals should be established.
Social organisations and residents should be encouraged to report violations, said Huynh.