An outbreak of salmonella was found in the stock of battery hens at the farm, with the decision made to slaughter a large portion in an effort to contain the outbreak.

Of 330,000 stock, 55,000 were killed, according to BNS. Gassing was used to carry out the operation; however some hens had escaped their cages and air guns were then used to kill these.

"Behaving in such a way toward animals is unacceptable," said Kristina Mering, president of Nahtamatud Loomad, an organization which highlights the plight of animals used in farming, including battery hens. Footage of the incident was obtained by the Estonian Society for the Protection of Animals (ESPA).

"In addition to the hens being denied a dignified life due to their confinement in cages, the footage also shows that they were denied their right to a dignified torture-free death," Mering continued, noting that the footage draws attention to the unethical farming of hens in battery cages more broadly.

The name and location of the farm in question was not reported.

Studies suggest that battery farming increases the likelihood of salmonella outbreaks, compared with free-range hens, leading to the bacteria infected eggs sold to market.

A single battery cage can reportedly hold 60 hens, with around an A4 paper-sized space afforded per hen. Caged hens also reportedly suffer psychological problems and are known to peck at each other's feathers.

Nahtamatud Loomad says it has already convinced 40 percent of Estonia's retail sector to stop selling battery hen eggs by 2025.

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