Police said three people were arrested on suspicion of burglary at the site, a 29-year-old man from Sheffield, a 23-year-old man from York, and a 33-year-old woman, of no known address.
Nine people from addresses across the UK were also arrested on suspicion of aggravated trespass in connection with the protest.
Two others were arrested at Stevenage police station on suspicion of burglary, the force said.
It added: “Our aim is to ensure staff at the site are able to go about their lawful work, while protesters are able to express their views peacefully and safely, within the law.”
In photographs released by Animal Rebellion, protesters appeared to pass a dog over the top of a metal fence.
The protest group said in a statement it was “not true” that animal testing was necessary.
“There are better alternatives,” it said.
MBR Acres said it was “a fully licensed establishment and a lawful breeder of beagle dogs that are specially bred for human and animal research in an environment compliant with our licences”.
In a statement it said it was “appalled by these actions”.
