"A Very Silent Night" is said to have been recorded at such a high sound frequency that only dogs can hear it, The Daily Telegraph reported Sunday.

The song was issued as a CD by the Royal New Zealand Society for the Prevention of Cruelty to Animals just before Christmas as a fundraiser.

The novelty song sold 6,000 CDs, a considerable achievement in the tiny New Zealand market. Now distributors in the United States and Australia are vying for the rights to international sales, the society has announced.

"We are delighted with the success of the CD in New Zealand, and are very grateful for the time and expertise given," said Bob Kerridge, chief executive of the RNZSPCA.