The operations at ninty-seven farms had been "blocked" while the NVWA investigated whether the banned substance was present.
Risk-based samples were taken, with no residues of furazolidone found, therefore the NVWA has given the green light for the pigs to be released.
The investigation had been prompted by the earlier discovery of the banned antibiotic in a calf, which was found to have originated from its feed. The NVWA begun the process of investigating all other farms which had also received this batch of feed.
Last month the NVWA announced it was investigating a manufacturer of animal feed which was suspected of having produced feed which had been contaminated with the prohibited substance.
Its Intelligence and Investigation Service searched an office building and house used by a feed manufacturer as part of a criminal investigation into the use of the banned substance, with documents seized as the search for further investigation.
Furazolidone has been banned in food producing animals in the European Union since 1995, because it is potentially carcinogenic. Eating meat from animals treated with this medicine may have harmful effects on human health, said a statement from the country’s Public Prosecution Service.