Duration of daily test pup exposure in adult, nulliparous rats alters maternal behavior induction rates: implications for animal use numbers.

Testing for the induction of maternal behavior in rats involves the use of adult nulliparous experimental females, lactating donor dams, and their pups. In the present study, the effects of reducing the daily pup exposure from 23 h to 1 h on maternal induction latencies were assessed. In addition, because a 1-h daily exposure would reduce the non-nutritive period and potential discomfort in the pups, the effect of the reduction in pup exposure on animal use numbers was compared under these two conditions. Exposure to test young for 23 h daily for 15 days significantly increased the proportion of test animals that became maternal compared with 1 h of exposure (92% versus 35%). Moreover, animals in the 23-h group that became maternal had shorter latencies (5 days versus 11 days) and responded faster to the pups on the first day that maternal behavior was displayed than did the 1-h exposure group. A mathematical comparison of numbers of rats required to induce maternal behavior in 30 nulliparous rats under both exposure conditions revealed that the 1-h group requires 2.6 times more animals. These findings indicate that compared with the 1-h scheme, the 23-h exposure protocol is significantly more efficient in both inducing maternal care as well as reducing the overall use of animals. Therefore, when selecting an animal testing protocol, one must consider the effect of reducing potential pup discomfort in light of the implications on the number of animals used and the behavioral outcome in a given test paradigm.