Some recommendations in the latest Guide for the Care and Use of Laboratory Animals (see http://go.nature.com/i9y7fr) have stirred up controversy in the research community. As former members of the committee that updated the guide, we would like to comment informally on these objections (see disclaimer).

The guide was released last year by the US National Research Council. Recommendations may apply to institutions funded by the US Public Health Service, but will, however, be used by the Association for the Assessment and Accreditation of Laboratory Animal Care International, a non-profit organization based in Frederick, Maryland, to evaluate and accredit research institutions.

Because of its many users and settings, the guide is written in broad statements of desired outcomes (performance standards) and is largely devoid of detailed specifications. This enables research institutions to create customized procedures and programmes within the context of the recommendations for high-quality care, from external acquisition or in-house breeding of lab animals to their final disposition.

The latest edition of the guide expands on this approach, partly on the basis of overwhelming support for performance standards by the research community. Despite this, some are urging the National Institutes of Health's Office of Laboratory Animal Welfare (OLAW) not to adopt the eighth edition, spurred by fears over how OLAW will interpret and implement the guide's recommendations. OLAW is currently considering implementation of the guide and is due to issue a position statement soon.

Objections mainly focus on the guide's space recommendations, particularly for breeding rodents. Optimal space requirements depend on factors including strain, sex, age, enrichment and animal psychology. The guide points out the necessity for study and assessment of the space requirements of laboratory species, while leaving previous recommendations essentially unaltered. Emphasis is placed instead on performance standards that are critical for deciding on minimal cage space.

Lobby groups representing commercial rodent vendors (among others) estimate that compliance with this new standard will cost upwards of US$500 million. But many institutions have already implemented performance standards to prevent overcrowding or are voluntarily using larger breeding cages. Standards for rodent husbandry should not be bound by commercial profitability.

Further research is needed into space and housing requirements and the provision of enrichment, exercise and human contact. We believe that the latest recommendations and a performance-standards approach will eventually help to define the highest welfare standards for research animals.