Boyle, 55, the creative genius behind the Games' opening gala, recently unveiled the details behind the July 27 spectacular, reported Sun online.
The show will be a green pastoral scene, including 70 sheep, 12 horses, 10 chickens, three sheep dogs, real grass and a plough.
"This is wrong on so many levels. Why would anyone think it was a good idea to subject farmed animals to the pandemonium of an Olympic opening ceremony?
"It smacks of the Roman gladiatorial arena. Many of those animals, especially the sheep, are likely to be terrified. (It's) exploitative and potentially cruel," campaigns director Justin Kerswell said.
A representative for Olympic Games organiser LOCOG said, "The welfare of the animals in the opening ceremony is of the utmost importance."