The RSPA say it is finding it harder to rehome abandoned pets, with 12,711 dogs rehomed in 2011, compared with 16,659 in 2009.
They rehomed 29,880 cats in 2011, less than the 36,070 two years before.
Both species are taking longer to rehabilitate and rehome than a year ago meaning their average cost of stay is also rising, the RSPCA said.
The average stay for a dog in the year so far is 59 days, five more than last year and their average cost of stay has risen from £810 to £885.
Cats have also averaged stays of 59 days this year, four more days than in 2011 and the average cost of their stay as risen to £554.60 from £517.