The body was found in September last year at Associated Waste Management in Shipley, near Bradford, by a worker sorting recyclable material brought in from households across Bradford, Leeds and parts of North Yorkshire.
It is believed the body had been placed in a household rubbish bin and transported to the plant by lorry.
Experts said the baby had been dead for a few days before it was found.
Tests determined that the baby had been born four weeks prematurely and may have been alive at birth, although this could not be proved. The baby was white and had blonde or light brown hair.
An inquest in Bradford yesterday heard from recycling plant worker Gary Normington who was sifting recyclable material when he saw what he thought was a chicken carcass.
“I took a second look and immediately saw what looked like a head. I stopped the conveyor and said something like ‘it’s a baby’.
“I started to feel sick and went outside.”
Mr Normington said he was very distressed by the incident as he once had a stillborn baby of his own.
“The image will stay with me for a long time. The whole incident has made me feel awful and physically sick.”
Detective Constable Jim Harrison, of West Yorkshire Police, said the mother had not been found despite five media appeals and a leaflet drop to 35,000 households.
He said 15 women had been investigated but all had been ruled out.
The inquest heard that the body of a baby girl had been found at the same site 18 months earlier but there was no DNA link to the boy.
Police had hoped to trace the mother using DNA from the body but only a partial profile was found.
This partial profile did not match any women on the West Yorkshire or North Yorkshire databases.
A post mortem examination revealed numerous fractures to the body which were probably caused by sorting machines at the waste depot.
The unclothed body had an umbilical cord stump but there wasn’t a clip attached.
Coroner Oliver Longstaff, who recorded an open verdict, said it was not known how or where the baby died.
He said it was not possible to be certain whether the baby was stillborn or not.
“On the balance of probability, I cautiously express the view that it is slightly more likely than not that this baby was born alive and then died.”
He said the police investigation remained open and he hoped the mother could still get help.
“The mother may still require assistance as a result of this very sad case.”