Dec 21 (Reuters) - Dairy producer Synlait Milk said on Monday its full-year profit would halve as a result of key customer and shareholder a2 Milk trimming its guidance after the COVID-19 pandemic hit demand in China.

Synlait now expects net profit after tax for fiscal 2021 to be about half of last year's result, and total consumer-packaged infant formula volumes to be about 35% lower.

The company's net profit after tax for the 12 months to July 31 had come at NZ$75.2 million ($53.54 million).

a2 Milk on Friday lowered its half yearly and full yearly revenue guidance.

Synlait told shareholders that there has been no disruption to manufacturing or demand for its lactoferrin ingredient or consumer-goods businesses, and said it was actively taking steps mitigate the impact of this development.

($1 = 1.4045 New Zealand dollars) (Reporting by Arundhati Dutta in Bengaluru; Editing by Angus MacSwan and Jane Merriman)