Madonna may want to cross the RSPCA off her Christmas list.

The singer has reportedly outraged the animal rights group after dyeing her pet sheep different colours for a photo shoot.

The 49-year-old and director hubby Guy Ritchie have been branded "irresponsible" after colouring their sheep blue, pink, yellow and green for a Vogue spread at their English country estate, in Wiltshire, England.

A spokesman for the Royal Society for the Prevention of Cruelty to Animals (RSPCA) said: "Why is it necessary and what are they trying to prove? It is an irresponsible publicity stunt."

The couple say the shoot - which will feature in new book Vogue Living: House, Gardens, People - was staged in homage to legendary photographer Cecil Beaton. 

Yet the pair insist that the dye used was temporary and did not harm the animals.

However, the RSPCA do not accept their reasoning, and are adamant the stunt could lead to dangerous copycat incidents.

The source added: "We would really question the need to do it. It really does send out the wrong message about how to use animals.

"Animals used in this sort of publicity stunt can lead to copycats. Even if the dye used in this instance is safe for the animals, other people might copy it with a dye that isn't safe."