Measuring Temporal Patterns of the Nest-building Process in Mice for Animal Welfare and Disease Monitoring

Nesting behavior in rodents is a species-typical ethological behavior used as a naturalistic instrument for measuring animal welfare/illness and behavioral aspects related to instrumental tasks. It is also proposed as valuable for disease monitoring, evaluating potential risk factors and preventive/therapeutical interventions. The reliability of Deacon’s scale to score nests at 24 h is well-recognized, and it is based on a 5-point ordinal scale ranging from 'not noticeably touched nesting material' to 'perfect nest'. In previous work using an animal model of Alzheimer's disease and wild-type counterparts, we proposed a 3-day protocol to discard false negatives, thus unveiling genotype-, sex- and age-dependent differences. Now, we propose the size of nesting as a numeric variable complementary to the ordinal scale. This would allow the required parametric repeated measures analysis to identify and evaluate temporal patterns in the nest-building process. For this purpose, nests of male and female mice with normal (C57BL/6) and AD-pathological aging were measured using paper nesting material and our 3-days protocol. The results showed that the nest-building process responded to a linear equation in wild-type animals or when female sex was considered. However, the lineal progression was found disrupted in males or the AD-genotype. Genotype per sex interaction indicated that the nest-building process was optimal in wild-type females, as they build the best nests at 72h. On each day, data were consistent with the ordinal scale, but the identification of temporal patterns with the numeric variable confirmed nest-building as a complex process, which is sensitive to sex and genotype.