The matriarch of the Oregon Zoo's Asian elephant heard wil be euthanized, zookeepers have decided.

Oregon Zoo

Pet (smaller elephant) nuzzles her daughter, Shine.

The female elephant named Pet is estimated to be 51 years old.

An infection in one of her front feet has invaded the bone, despite powerful antibiotics. Zookeepers have agonized over the decision, but they fear that Pet will not be able to walk soon.

A veterinarian expects to use a powerful narcotic to put the three-ton elephant to sleep next week, and then give her an overdose of the drug. Pet is the matriarch of the elephant herd, one of the zoo's most popular exhibits.