Non-human primates used in biomedical research are highly social animals, and solitary housing is a recognised welfare failure that causes psychological suffering.
Solitary housing of highly social primate species represents one of the clearest and most serious welfare failures in laboratory animal care. Primates evolved for continuous social interaction; isolation causes chronic stress, behavioural abnormalities and physical health deterioration. Regulatory requirements for social housing exist but are frequently overridden by claimed scientific necessity that is often not rigorously justified. Research facilities that have committed to social housing consistently report that the great majority of protocols are compatible with pair or group housing. Welfare monitoring of individually housed primates through health checks, behavioural scoring and environmental enrichment is a minimum standard, but social housing should be the default with isolation as the exception requiring specific justification.