It is the product's therapeutic potential that makes it stand out, according to producers and buyers.
Machines long ago usurped a donkey's traditional role as the farmer's beast of burden, but the animals are winning new fans in Montenegro -- thanks to their luxury milk.
It comes at a trickle and selling at a hefty 50 euros ($54) per litre it could provide a lifeline for the Balkan donkey breed, whose numbers have sharply declined.
But it is the product's therapeutic potential that makes it stand out, according to producers and buyers.
"This milk is extremely healthy for skin disease and other diseases," said Darko Saveljic as he squeezed an inch of the white stuff from Tereza, one of 30 donkeys at his sanctuary in the central Montenegrin countryside.
Even small daily amounts can help tackle asthma and bronchitis, he said.
The animals are first milked just two to three months after giving birth and produce only 400 millilitres a day, a fraction of what a cow can provide.
"Don't expect a lot of milk," warned Saveljic, who gives away half his yield to those he thinks will benefit but cannot afford it.
The product's price tag is significant in Montenegro, home to 620,000 people and an average monthly wage of about 500 euros.
About half an hour away in the capital Podgorica, Valeria Markovic contacted the farm after searching online for a cure for her five-year-old son Vlado, whose allergies were making it difficult for him to breathe at night.
"I'd only read that Cleopatra bathed in donkey milk," said Markovic, an economist, laughing about her discovery. "I didn't have any idea about it."
After drinking a small amount each day, Vlado's symptoms became "milder than they were before."
Photis Papademas, a dairy science expert and assistant professor at Cyprus University of Technology, said there are strong indications that donkey milk is effective against disorders resulting from a poor immune system.
He said the composition of proteins in the animal's milk -- which is similar to human milk but lower in fat -- appeared to regulate immunity, but clinical studies are needed.
"The proof is not very strong yet, but there are very good indications," he told AFP. "You have to be very cautious when connecting health and food."
Donkey products are also promoted in Serbia, where the Zasavica Nature Reserve claims to sell the world's most expensive cheese -- made from donkey milk -- for 6,000 dinars (48 euros) per 50 grams.
Montenegro's last agricultural census in 2010 put the donkey population at around 500, although Saveljic estimates there are now only 150, and this year the animal was included in a national conservation programme for indigenous breeds.
Three decades ago "not any house in the villages in this Mediterranean part of the country was without donkeys, thousands of donkeys, and now we're using machines and donkeys are animals for nothing," he said.
For 42-year-old Saveljic, producing milk is just one of the functions of his sanctuary and a way to keep it sustainable.
An ornithologist by training, he set up the farm over a year ago to preserve the mountainous country's donkeys, alarmed by dwindling numbers of the indigenous and domesticated Balkan breed.
All known by name to their new owner, they now live out their days peacefully with a few roaming chickens and guinea fowl for company -- and plenty of treats.
The entrance fee to the sanctuary is one kilo of apples or carrots, and Saveljic hopes that welcoming visitors each weekend will raise awareness.
He also invites families with autistic children to visit for free, saying parents report positive behavioural changes after they interact with the animals.
"If you work with donkeys well, donkeys are like dogs. They respect you, they are really ready to go with you everywhere," Saveljic said.