NEW YORK — Petco, the pet store chain, went public again Thursday, hoping to cash in on people’s obsessions with their furry pets.

Petco’s stock, which opened at $18 Thursday, soared 60% to $29.26 in afternoon trading, valuing the company at more than $6 billion. It raised $864 million, after selling 48 million shares in its initial public offering. The company plans to use that money to pay off debt.

It’s the third time Petco has gone public since it was founded in 1965 as a mail-order veterinary supplies business. Both times Petco was bought and taken private, most recently in 2006.

Much has changed since then. Pets, which were once banished to the backyard, are now sleeping in human beds as Americans increasingly treat their cats and dogs like family members. Spending on treats, medicine and pet-sitting is expected to reach a record $99 billion last year, according to the American Pet Products Association.

To lure free-spending pet parents, San Diego-based Petco has been shaking up its image as more than just a place to buy kibble. At its nearly 1,500 stores, dogs can get a fur trim, visit a vet, take a training class or try on a new outfit.