Celebrities including Jamie Oliver, Sara Cox and Jarvis Cocker attended Thursday's launch - but Banksy himself left before the party to avoid the spotlight.
Banksy, from Bristol and whose real name is Robin Banks, has been hailed as "Britain's most celebrated graffiti artist" and designed Blur's latest album cover.
He avoids exhibiting in galleries - but his latest show, Turf War, has taken over a warehouse in east London for five days.
The exhibition includes pigs painted in police colours, sheep painted in concentration camp stripes and a cow covered in images of Andy Warhol's face.
They are all show animals from Cheddar, Somerset, which are used to being on public view, and the paint was animal-friendly, a spokeswoman said.
Protest
And an inspector from the RSPCA approved the animals' conditions, she added.
"I think he was a bit dazed by the whole event. But he OK'd it all."
But one woman took offence to animals being used as art, and chained herself to railings surrounding a decorated cow.
Debbie Young and two other protesters were demonstrating at what they saw as animal cruelty.
Turf War also includes a sculpture of Rodin's The Thinker with a traffic cone on its head and "piles of burnt-out police cars".
Banksy, who prefers to avoid publicity to retain his anonymity, left the warehouse at about 1700 BST on Thursday - before the party started.
The spokeswoman said the exhibition did not mark Banksy's entrance into mainstream culture.
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