Health staff were split into two groups and 24 workers were tested at one time, which took about 10 minutes per person.
Findlay said Alliance staff had been "very welcoming to health professionals and keen to participate".
• Covid19.govt.nz: The Government's official Covid-19 advisory website
"They [Alliance staff] feel its important that we do this work to know whether there are any pockets of the virus in the community and so they feel like they're helping out."
Ongoing testing would mean health officials would have a better idea of when it was safest to move from Alert Level 3 to Level 2.
Health professionals had come from Queenstown, Wanaka and Dunedin to help Southland staff carry out testing efficiently.
Alliance Group chief executive David Surveyor said the co-operative wanted to "play its part" in the fight against Covid-19.
Tests would be carried out at the Pukeuri plant near Oamaru next week.