The plants in Northern Ireland have reported good supplies of lambs coming forward for slaughter with 13,314 lambs killed in the North last week, the Livestock and Meat Commission (LMC) has said.
This takes total lamb throughput for September to 52,384 head, which it said is an 8% increase on September 2014 levels when 48,600 lambs were killed in plants in Northern Ireland.
A further 7,388 sheep were exported from the North to the Republic for direct slaughter last week.
The LMC said that the Republic provides an important alternative market for the Northern Ireland sheep industry. During 2014 exports to the Republic for direct slaughter accounted for 43% of total output from the North's sheep flock, it said.
During 2015, as of mid-September 38% of Northern Ireland origin sheep slaughtered were killed in plants in the Republic.
Republic's sheep kill running 1% ahead of last year's levels
The national sheep kill to date is running 1% ahead of 2014 levels, figures from the Department of Agriculture show.
According to the figures for the week ending September 27, the total cumulative kill at export sheep meat plants has increased by 13,672 head on 2014 levels, with 1.88m sheep slaughtered in 2015.
However, despite the cumulative increase, the weekly kill has dropped by 3% on the corresponding week last year.
This reduction in slaughterings has occurred due to a smaller number of 2014 born lambs and cast (ewes and rams) slaughterings.
Weekly slaughterings of these lots have dropped by 29% (3,249) and 93% (1,476) respectively.
The figures from the Department of Agriculture also show that the cumulative number of spring lambs slaughtered in Irish plants has increased by 9%, while the weekly kill is up by 5% or 88,557 and 2,780 head of sheep respectively.