A pair of Chinese abattoirs have been accused of pumping cows with water for up to 12 hours, to artificially increase their weight before slaughter.

Video footage showed cattle tied to railings with plastic tubes forced up their nostrils. One was seen lying on its side with water pouring out of its nose.

Police arrested dozens of workers in eastern China's Anhui province last week, according to the South China Morning Post which originally reported the story.

"Clearly this is a highly invasive and deeply unpleasant thing to do to any animal, but particularly animals already likely very stressed and fearful from being in the slaughterhouse environment in the first place," Wendy Higgins, a director at Humane Society International, told The Independent.

"These are sentient animals who feel pain, fear, and anticipate danger. And so to see these cows have their final hours made that much worse by yet another painful indignity, is just heartbreaking."

Calling the procedure "disgusting", she added: "You can clearly see from the video these cows are in distress, with one eventually collapsing on the floor."

An employee at one of the abattoirs, in Quanjiao county, told the Morning Post that pumping the animals with water added five to 10 kilograms to their weight.

The process was repeated daily from 7pm through to dawn, one of them said, adding: “We find it hard to watch the animals as well, we do not want to do it.”

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Most of the meat was bought for school canteens, according to undercover journalists who found it being sold for as little as £3.36 per kilogram in wholesale markets in Nanjing.

Staff at the second slaughterhouse, in Laian county, reportedly admitted to police they used water to increase the cows’ weight, adding their boss told them to remove the pipes “if anyone ever knocked on the door”.

The manager of the Laian slaughterhouse denied the claims, insisting the pipes were used to clean the animals’ stomachs.

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A vet at Compassion in World Farming, an animal welfare organisation, said the procedure was "clearly causing great distress and discomfort" to the animals and that forcing cows to consume too much water would interfere with breathing.

If the tube was inserted into the lungs in error, "the water would slowly drown the animal", Inês Ajuda said.

According to Drovers, a publicatn dedicated to the cattle trade, Chinese consumption of beef in 2018 is estimated at 8.6 million tons, second only to the US.