The Memorial Day holiday in the United States also contributed to the reduction.
In Canada, it was the former XL Packers plant at Brooks, Alta., that was shut down because it is now owned by JBS USA.
Beef production was down 14.5 per cent last week from the prior week at an estimated 443 million pounds.
That compares to a decline of 4.5 per cent for the same holiday-shortened week in 2019, said the Daily Livestock Report which is published by Steiner Consulting Group. Slaughter last week was about 50,000 head below the same period in 2019.
The publication said it will take some time to catch up on the backlog of slaughter-ready cattle, but will be faster for hogs.
The report said pork production last week at 424.4 million pounds, down by 17 per cent from the previous week and by 7.5 per cent from the same week in 2019.
The extent of the cyberattack's impact on broiler production will become clearer when the United States Department of Agriculture releases its estimates later this week.
