Effects of cage-cleaning frequency on laboratory rat reproduction, cannibalism, and welfare.
Regular cage-cleaning is important for health, but for breeding rats it disrupts the nest and removes olfactory signals important for parental care. To investigate how different cage-cleaning frequencies affect breeding rats' health and welfare, we monitored reproductive output, pup mortality, pup sex-ratios, parental chromodacryorrhoea and in-cage ammonia levels for rats in a commercial breeding facility. Cages were cleaned twice-weekly, once-weekly or every two weeks (18 cages/group), replicated in two buildings, for the entire 36-week reproductive period. Frequent cage-cleaning had no clear benefits or major negative effects, showing no significant reductions in ammonia levels, or affects on health or overall pup mortality. However, frequent cage-cleaning slightly but significantly increased cannibalistic behaviour. This was because: (i) vulnerable 0-2 day old pups were more likely to be exposed to a cage-cleaning event in the more frequent cage-cleaning regimes, physically disturbing them, and disrupting the nest and scent marks; and (ii) in the twice-weekly and weekly-cleaned groups, pups under 2 days old at their first cage cleaning were more likely to be cannibalised. Possible mechanisms behind these effects are discussed, including that cleaning might induce premature births, or stress the parents through noise or olfactory and physical disturbance. Finally, the cage cleaning frequency producing most pups differed between the two buildings – an interactive effect corroborating previous findings that same-strain rodents’ phenotypes can differ with environment. Overall, we suggest that for breeding rats, cage-cleaning regimes should minimise noise, dissemination of unfamiliar conspecific odours, and physical disturbance during very late pregnancy and the first days following birth.