A woman has pleaded guilty to 12 offences of animal rights extremism.
Darley Oaks Farm closed in January 2006
Deborah Morrison, 35, from Dorchester, Dorset, pleaded guilty to the offences which include six charges of blackmail at Stafford Crown Court.
The offences involved sending threatening letters and emails to companies and individuals, said police.
One of the firms had links with Darley Oaks Farm in Newchurch, Staffordshire. Morrison was granted bail and the case was adjourned for pre-sentence reports.
The date of sentencing is yet to be fixed.
Most of the victims who received letters and emails had connections with animal research organisations, said Staffordshire Police.
The companies involved included Darley Oaks Farm, which bred guinea pigs for research until January 2006.
Morrison also pleaded guilty to one charge of attempted blackmail, three charges of interference with a contractual relationship so as to harm an animal research organisation, and two charges of attempting to interfere with contractual links to animal research organisations.