The eighth edition of the Guide for the Care and Use of Laboratory Animals, published last year, calls for new size requirements for cages with litters, and researchers worry that compliance will be costly, Nature reported. The new guidelines, which apply to breeding mice and rats, state that  rat mothers and their pups should receive a minimum of about 800 square centimeters (125 square inches) of floor space, with single adult getting about 450 square centimeters. For mice, 330 square centimeters are recommended for a mouse litter, and 97 square centimeters for adults weighing over 25 grams. Though previous editions did not explicitly outline minimum cage size requirements, researchers see the new guidelines are a significant step up from current US practices.

Some researchers have reacted with consternation, calculating that meeting the requirements could increase their rodent care budgets by hundreds of thousands of dollars....

However, the guidebook’s authors at the US National Academies and National Institutes of Health officials argued that the guidelines are merely starting points and are open to interpretation by each institution as necessary. The NIH has already adopted the new guide in its own facilites, and the Association for Assessment and Accreditation of Laboratory Animal Care International is implementing the new standards as well.

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