Seven baby monkeys died of poisoning at one of the biggest primate research centres in the US, according to a report shared with The Guardian.

The deaths of the monkeys were described as an accident brought about when a mother was marked with dye. 

After being reunited with her children, the dye was transferred to the young macaques and poisoned them fatally.

One of the babies was only a day old and none were older than a few weeks. 

The incidents were reported to government authorities last year and recently updated in a letter sent to the Guardian.

UC Davis told watchdog the Office of Laboratory Animal Welfare the babies suffered from ‘weakness and respiratory distress’ and dye was found on their lips and tongues.

Two macaques had “severe edema and swelling of the larynx and tongue”. All seven animals were found with dye on their mouths, fur or skin.

The watchdog said from now on infants should be kept away from the deadly dye and mothers tested on should be separated from their offspring for longer.

The centre keeps 4,200 primates used to research HIV/Aids, Zika virus and other infectious diseases, respiratory disease, reproductive health, Alzheimer’s disease and ageing.

UC Davis was also investigated in 2016 over abuse to its primates. The investigation discovered that multiple primates had fractured bones while trying to escape through an unsecured door at the centre.

And in 2005 seven monkeys died from heat overexposure, for which the US Department of Agriculture subsequently handed the university a $4,815 fine.

A UC Davis spokesman said in a statement that primates are kept in extended family groups at the centre, get regular medical exams and live up to 38 years.

“We strive to take the best possible care of animals in our charge,” they said, adding that “center staff changed procedures so they no longer dye-mark monkeys under six months of age and take other steps to minimize dye transfer”.

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