The milestone lamb was from Peter McCrostie, a Kaitangata sheep and beef farmer whose family estate has supplied livestock to Finegand for much of the plant's 99-year history.
The chosen carcass made its way down the chain about 12.15pm, workers and plant management taking photographs as it went.
Mr Williams, cooling floor supervisor, has worked for nearly 51 years at Finegand, and for him it was a proud day, the latest in a string of plant milestones, including the first time it processed more than one million lambs in a season (1959) and its 50th anniversary celebration.
Mechanisation and awareness of health and safety had given workers longevity in what was once an extremely hard and dangerous industry.
In the old days, accidents were common, and the way they were dealt with was very different than today. If a worker was cut, he was stitched and back on the chain within half an hour. If an injury was chronic, such as a repetitive strain, they were often told to leave.
"They would just say 'You're not suited for this kind of work'," Mr Williams said.
The move to chilling meat, rather than freezing it, in the late 1970s, meant strict hygiene measures. Smoking on the chain was banned and proper hand-washing introduced.
Once, only cold sloshing water in a drum was available for washing while working, and Mr Williams remembered the feeling of fat accumulating on the hairs of his arms.
"At the end of the day, your arm was half as big again," he said.
A slaughterman for 48 years, Mr Brown said the job, while still repetitive, was not "drudgery" any more.
He valued the many friendships made on the job.
"It's not the buildings ... it's the mates and the people you work for, that's the real thing."
Both men have sons employed at the plant, and agreed the makeup of the workforce had changed significantly.
Once, there had been no women, plenty of "cockies' sons" saving to buy a farm, and a big contingent of itinerant butchers following the killing season through New Zealand and Australia.
And a hostel over the road from the plant once housed up to 180 workers.
