Abattoir at centre of animal cruelty allegations in clear after 20-month investigation

Animal rights campaigners say they are "very disappointed" after a Tasmanian meatworks accused of animal cruelty was cleared after factory inspections, and footage from activists was deemed unusable as evidence.

The allegations against Gretna Quality Meats, revealed in an ABC report featuring video of a series of alleged mistreatments of livestock in 2016, were the subject of a prolonged investigation by the Department of Primary Industries, Parks, Water and Environment (DPIPWE).

The footage was obtained with hidden cameras installed by unidentified activists at a number of locations within the facility and given to media by Animal Liberation Tasmania.

On Monday, the department announced the probe as being finalised, with the decision being taken that no further action would take place.

In a statement, Biosecurity Tasmania general manager Lloyd Klumpp said "no prosecution will be undertaken following ongoing audits of the facility, as well as a review of DPIPWE's investigation by the Director of Public Prosecutions".

"Our ongoing audits of the facility have found the facility is complying with its requirements in relation to animal welfare," Dr Klumpp said.

"An investigation of the allegations made against the facility was also considered by the DPP … who had determined there is no reasonable prospect of conviction on the allegations and based on that no prosecution should be undertaken."

The footage, purportedly filmed over several days and showing workers at the facility handling the livestock, was considered as part of the investigation, Dr Klumpp said, adding "anonymously-supplied footage is rarely admissible in court matters due to the potential for it to be edited and spliced".

Gretna Meatworks owner Michael Munnings said he had cooperated with investigators.

"They looked at the plant, they looked at the way we process stock. We had Biosecurity [Tasmania] here on a number of occasions.

"We still have random drop-in visits by biosecurity and we've complied with all our audit requirements, as well."

Animal Liberation Tasmania campaign director Mehr Gupta said she was "very, very disappointed" at the decision not to pursue action.

"Unfortunately, we're not completely surprised," she said.

Ms Gupta said if the activists came forward to give evidence, along with the video to increase the likelihood of prosecution, they could face prosecution themselves.

The airing of Animal Liberation-supplied vision shot covertly at another Tasmanian facility in 2016 prompted the operator of the meatworks to admit mistreatment of animals had occurred, but that the workers involved were no longer employed and the company was working to ensure it did not happen again.

The delays in the DPIPWE meatworks investigations and lack of information regarding the deaths of 16 polo ponies in the back of a truck that crossed Bass Strait on the Spirit of Tasmania in January were cited as reasons behind the resignation of a long-term adviser to the Tasmanian Government on animal welfare.

DPIPWE has been approached by the ABC for comment about the Gretna Quality Meats decision.