The RSPCA has increased the circulation of some editions of its quarterly magazine by 1,400 per cent from 30,000 to 450,000.
The animal life magazine, first published in 1990, was previously sent only to RSPCA members, but will now be sent twice a year to direct debit donors, cash givers and people who have pledged to remember the charity in their wills.
A spokeswoman for the RSPCA said the costs of expanding the circulation were not yet known, but some would be covered by increased advertising revenue.
She said the charity aimed to encourage people to continue to donate by giving them a fuller understanding of its work, which would, in turn, help it retain supporters for longer.
"We're confident the benefits will outweigh the costs," she said.
The spring issue is the first of two bumper runs this year. The circulation of the summer and winter issues will remain unchanged.
The spokeswoman said the magazine was printed on paper certified as Forest Stewardship Council stock and recyclable.