RESUMO
Many people who work in laboratory rodent breeding facilities believe that disrupting certain sensitive rodent lines will result in increased breeding failures and loss of newborn pups. To evaluate this hypothesis, the authors assessed the effect of cage-change frequency on the breeding performances of a mouse strain (C57BL/6NTac) and a rat stock (NTac:NIH-Whn) that were thought to be sensitive to disruption. As per recommendations in the Guide for the Care and Use of Laboratory Animals, personnel changed one half of the breeding cages weekly, regardless of the presence of newborn pups. The other breeding cages were also changed weekly, unless newborn pups were present, in which case the cages were not changed until the following week. The authors assessed breeding performance by calculating the production efficiency index (the total number of pups that survived to weaning divided by the total number of actively breeding females). Breeding performance did not differ significantly between rodents whose cages were changed weekly and those whose pups were not disturbed.