BUENOS AIRES, Nov 5 (Reuters) - Argentine scientists have found a way to make cows produce more milk by injecting them with a bovine growth hormone produced by cloned and genetically modified dairy cows.

Synthetic bovine somatotropin, which is also called rbST, is already injected into cows to boost milk production, but Argentine researchers say their method is cheaper and produces a natural bovine hormone.

Andres Bercovich, head of research and development at biotechnology firm Bio Sidus, said that if a cow would normally produce 5.3 gallons (20 litres) of milk per day, it could produce more than 6 gallons (24 to 25 litres) when it is injected with the hormone.

"It's going to be a cheaper method because it requires far less equipment and the only costs are what the animal needs," he told Reuters on Wednesday.

Bio Sidus started cloning cows in 2002 and since then it has developed animals capable of producing human growth hormone and insulin in their milk.

The hormones can be extracted from the cows' milk and used in the same way as synthetic hormones produced in laboratories from genetically engineered bacteria in tanks.

Bovine somatotropin has been approved for sale in the United States since 1993, but it has been banned in Japan, Australia, Canada and parts of Europe.

Opponents say it can have harmful effects on cows and humans and recently there has been a backlash against the synthetic hormone by food retailers and dairy manufacturers in the United States.

Bio Sidus aims to export the dairy hormone technology to the United States, Mexico, Brazil and Peru, but no date has yet been set and the company's cloned bovine hormone technology has not been approved for sale in Argentina. (Reporting by Karina Grazina; Writing by Helen Popper; Editing by Vicki Allen)

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