Norbrook Holdings, the Newry-based pharmaceutical firm, saw its pre-tax profits almost halve to ?4.2m in the past year.
Output was disrupted by the effect of the pandemic in the first half of the financial year.
Chief executive Liam Nagle said the firm lost 20% of its manufacturing capacity for a four-month period.
He said investments in factories and staff facilities allowed a return to full capacity later in the year.
Norbrook produces veterinary medicines and is one of Northern Ireland's biggest exporters.
Progress in US expansion
Mr Nagle said that "as with all businesses, the coronavirus has presented a number of significant issues for us to deal with, primarily around employee welfare, customer demand and operational challenges".
Turnover for the year was ?212m down 11% from ?237m in 2019.
Mr Nagle added that in spite of challenges the business was able to make good progress with its US expansion plans. pg
Turnover in the US was up by 6% on 2018 with sales of pet medicines up by 31%.
Norbrook employs about 1,800 people, mostly in Newry.
Mr Nagle said most non-manufacturing staff, about 400 people, had been working from home since March.