The city’s Animal Care Center is being investigated by the state Attorney General’s Office for euthanizing dozens of dogs and cats mere days after having them undergo painful neutering, The Post has learned.

Since January 2017, the ACC has euthanized at least six animals one day after neutering them, and killed at least another six two days later, public records show.

Six more animals were put down three days after the surgery, three days later, 11 after five days and eight after six days. Two more dogs were killed sometime within four days of being neutered, but it’s not clear exactly when.

“It’s reprehensible — there’s truly no words for it,’’ said Manhattan-based animal activist ­Judith Lustgarten.

“Who would put a defenseless soul through an operation to kill it immediately’’ afterward?

Animal-rights groups have been flooding the Attorney General’s Office with complaints, leading AG probers to request information last month from the ACC and ASPCA “as part of an investigation,” according to ­e-emails provided to The Post.

The ASPCA conducts about 25 percent of the taxpayer- and private-donor-funded spay and neuter services for the ACC, formerly known as Animal Care & Control.

The ACC touts neutering as a common practice designed to increase adoptions and reduce the amount of time animals need to spend in the shelter. State law requires that animals be neutered, before they can be adopted.

But advocates say the dozens of animals killed within days of the surgery point to a system that at best is mismanaged or at worst is run by heartless workers.

Last May, a dog named Duke was euthanized just three days after he was neutered, even though a qualified candidate was willing to adopt him.

“I was just heartbroken, honestly,’’ said the prospective adopter, who gave her name as Emily Ann. “It’s cruel to put them through a surgery just to put them down a few days later.’

An ACC rep — who asked not to be identified because she said she gets death threats — said her agency has “no indication’’ that it is being investigated. She added that the number of animals neutered and then quickly killed “represents less than 1 percent of the over 8,000 animals altered. It is still 1 percent too many.’’

The ASPCA said in a statement, “We do not own these animals, nor do we have influence over . . . any eventual outcome decisions ACC may make.”

Additional reporting by Tamar Lapin and Nolan Hicks