The laboratory rat : improved welfare for mothers andpups through breeding in an enriched environment?

Sammanfattning: Maternal behaviour is crucial for the development of the rat pups’ behaviour and stressresponses later in life. There are numerous studies evaluating the effects of the dams’behaviours on the pups, but not many addressing what can be made for wellbeing of the ratdams when breeding. Few studies have addressed the question of how the commonly usedrearing environment effects the dams’ behaviour and in the long run how it effect the ratsreared to become our research models. In this study, rats were therefore reared in twodifferent cage systems; one cage type with elevated top and enriched by a shelf and climbablenetting (RT) was compared to the type of cage most commonly used today, the makrolon typeIV cage (M IV). Dams were equipped with telemetrical devices to measure activity, bloodpressure and heart rate, and direct observations of their maternal behaviour were made. Urinecorticosterone/creatinine quote was measured and behavioural tests (defensive withdrawaltest, elevated plus maze test and open field with novel object) were performed in both damsand pups. The dams in the RT cages showed more activity and a transient increase in bloodpressure, and a tendency towards less urine corticosterone levels. They also spent less timelicking/grooming and arched back nursing their young. The pups showed differences in urinecorticosterone levels as well as in the behavioural tests, where the RT pups had significantlyless corticosterone excretion, and showed less fearful and anxiety-like behaviours in thebehavioural tests. There were greater differences between the groups of female pups thanbetween the male ones, pointing to the female pups being more sensitive to improvements ofthe environment. We have shown that the rat dams’ activity increases and stress decreases inthe RT enriched cage, and that the rat pups from the RT cages show less stress response, lessfearful and less anxiety-like behaviours even though the dams spend less timelicking/grooming and arched back nursing them. These findings support the argument that anenriched optimised environment and voluntary maternal separation give mentally healthierrats, possibly better as a model for mentally healthy humans.