12/31/2013 08:57 EST | Updated 03/02/2014 05:59 EST

'Sweetie' the Siberian tiger euthanized at Vancouver Zoo

The eldest tiger at the Greater Vancouver Zoo has been humanely euthanized after suffering breathing problems, a loss of appetite and ongoing lethargy.

'Sweetie', an 18-year-old Siberian tiger, had already been through a month of veterinary treatment, including medication and appetite stimulants, but her condition continued to decline.

According to a press release, Sweetie was born at the zoo and as such, outlived the median life expectancy for tigers born in captivity of 14 years.

In the wild, there are estimated to be as few as 400 – 500 Siberian Tigers living primarily in eastern Russia, although some exist in China and North Korea.

Tigers conservation status is listed as “vulnerable”  by the International Union of Conservation of Nature Red List.

A full necropsy, to determine exactly what cause Sweetie's decline, will be performed later today.