Their stomachs full of eggs, beer and coconut water, Nguyen Van Liet's prized white oxen streak ahead of their rivals to the cheer of tens of thousands of spectators in Vietnam's Mekong Delta.

The bovines and their owners gathered on a hot morning in a muddy field for the annual Bay Nui ox race — a celebrated ritual of Vietnam's Khmer minority, ethnic Cambodians living mostly in the country's south.

Out of action for two years due to the Covid-19 pandemic, many of the animals — racing in pairs — appeared a little rusty, running off the tracks to the disappointment of the vast crowd.

Liet's beloved oxen couple no.03, with their big dark eyes, long legs and curvy horns, looked as gentle as any ploughing the ricefields of southern Vietnam.

But their sweet appearance belied their strength on the field.

"Of the four tournaments they have entered, they have won three," Liet proudly told AFP before the race.

The competition — this year fought among 56 pairs of oxen— is held in An Giang province as part of the Sene Dolta festival, where the Khmer community remember their ancestors and hold a clutch of sports and art activities.

It's believed the race was once hosted by monks as an expression of gratitude to farmers who helped them plough their soil ahead of the new rice crop.

Muddy fun

In 2013, at a time when the average monthly income in rural areas was just $60, Liet spent around $700 on his young ox pair, determined to turn them into professional racers.

"As I had already raised oxen for ploughing, I could tell which ones were good or not," Liet said, explaining he learned from his grandfather and father, who raised oxen for years to work the family's rice fields.

"A race ox must be tall, fit and flexible," said Liet.

With machinery now largely doing the oxen's daily work in the Mekong Delta, many can focus on their training for months or even years before the race. They must be the perfect size — not too big and not too small — to reach their maximum speed.