WARNING: CONTAINS DISTRESSING CONTENT
The distressing clips have been released by German animal rights organisation Soko Tierschutz and Cruelty Free International, who claim to have uncovered monkeys being strapped into metal harnesses and kept in tiny containers at the lab in Mienenbüttel in Neu Wulmstorf, Lower Saxony.
Cats and dogs are also apparently left bleeding and dying following toxicity testing.
The footage was obtained as part of a joint operation, which saw an undercover worker secure a job at the lab after the LPT Laboratory of Pharmacology and Toxicology put out an advert for new employees in Autumn 2018.
Friedrich Mülln from Soko Tierschutz said: "In 2013, we also tried to get a job there, but were not successful. From December 2018 to March 2019, the undercover investigator worked in the lab."
The undercover worker reported seeing toxicology testing on the animals - including beagles, monkeys, cats and rabbits - supposedly carried out for companies in Germany as well as worldwide, claiming animals were kept in horrific conditions.
Beagles reportedly also had pipes forced down their throats and were given capsules, before being left to bleed and suffer following the experiments.
Mülln said: "The animals were even still waggling their tails when they were being taken to be killed, the dogs were desperate for human contact."
Photos also show monkeys strapped to seats in rows along the wall, while others have their heads in restraints - desperately trying to escape.
Mülln continued: "The worst treatment was kept for the monkeys. The macaques breed of monkeys are small, relatively light primates, which are often used for animal experiments at LPT.
"They are kept in cramped conditions in small cages. Many of the animals have developed compulsive tendencies and are seen going round in circles."
The cats, meanwhile, are reportedly given up to 13 injections per day by untrained professionals, and left to suffer.
The undercover activist also said the animals are treated with violence by the workers, who are not trained animal carers.
According to Cruelty Free International, LPT is a family-owned contract-testing laboratory carrying out toxicity testing for pharmaceutical, industrial and agro-chemical companies from all over the world, in order to meet the requirements of governments and regulatory authorities.
Cruelty Free International said: "Toxicity testing involves poisoning animals to see how much of a chemical or drug it takes to cause serious harm, in an attempt to measure what a 'safe' dose for humans might be.
"Animals are injected with or made to eat or inhale increasing amounts of a substance to measure the toxic effects which can be severe and include vomiting, internal bleeding, respiratory distress, fever, weight loss, lethargy, skin problems, organ failure and even death. No anaesthetics or pain relief are provided."
Michelle Thew, Chief Executive of Cruelty Free International, stated: "Our investigation has uncovered appalling animal suffering, inadequate care, poor practices and breaches of European and German law.
"We are calling for the Laboratory of Pharmacology and Toxicology (LPT) to be closed. We are also calling for a comprehensive review into the use of animals in regulatory toxicity testing in Europe, including the UK.
"Every investigation, without fail, shows a similar tale of misery and disregard of the law."
The animal activists have reported the case to police, who are investigating.
They are also calling for laws in Germany protecting animals to be tightened, arguing they are not strict enough.
LADbible has contacted LPT Laboratory of Pharmacology and Toxicology for comment.