An animal welfare worker who picked up a “sweet-natured” dog at a NSW pound was horrified to discover more than 100 metal pellets buried underneath its flesh.

The metal slugs, which came from a BB gun, couldn’t be seen on “Molly” the Kelpie cross’s body and were only picked up by a vet during a routine check-up.

A shocking photo of an X-ray, posted by the NSW Animal Welfare League (AWL) on Facebook , shows the metal pellets dotted all over Molly’s body.

AWL’s Senior vet Simone Maher, who examined Molly at her Kemps Creek clinic, was initially puzzled by the X-ray and believed her machine was faulty. But she re-did the X-ray with the same results.

A careful examination revealed there were indeed objects trapped underneath Molly’s skin, and the removal of one of the bumps revealed the shocking truth – they were the metal pellets of a BB gun.

Dr Maher told Nine.com.au the pellets did not appear to be causing her any pain and were probably at least a year old.

"There is little external evidence of the initial trauma that caused these pellets to become so diffusely lodged in Molly’s body, which would indicate it happened quite some time ago," Dr Maher said.

Erika Pankhurst, a AWL animal behaviourist, who picked up Molly from the pound to be rehomed by the welfare group, said she instantly drawn to the Kelpie cross.

"I fell in love with her because I love these types of dogs. They kind of look like your old farm dog. She was lovely, a little bit timid, but very sweet and very affectionate," she said.

Not expecting to hear of any health problems with Molly, Ms Pankhurst was shocked when she got an urgent call from the vet asking her to look at the x-ray.

"I just looked and it was I was like ‘I’ve never seen anything like this before. It was quite upsetting because she is so lovely."

"It makes me so upset that someone could do something so horrible to such a lovely dog, or to any dog."

The AWL was looking to find Molly a loving new home but in the meantime, staff at the AWL NSW office had fallen for their "Wonder Dog" and were busily spoiling her with lots of treats, she said.