Beyond comfort: Basic environmental enrichment accelerates sexual development in mouse pups

Most studies on environmental enrichment utilize 'super-enrichment' protocols, which are challenging to implement routinely in animal facilities; furthermore, few explore the effects of environmental enrichment on offspring development and fertility. The objectives of this study were to investigate the effects of standard housing (S) or basic environmental enrichment (EE) conditions across two experiments: 1) reproduction and fertility of adult male and female mice; and 2) physical, neurobiological, and sexual development of the offspring (F1) from S and EE dams (as well as from dams enriched only starting from mating -EEc-) including their fertility in adulthood. EEc group was included to distinguish F1 outcomes resulting from enrichment since birth versus those resulting from mother's pre-reproductive enrichment. Standard conditions involved group housing in polypropylene cages with wood shavings. For EE, paper strips and PVC tubes were added. Experiment 1 showed no differences in reproduction or fertility between S and EE mice, nor in reproductive endocrinology or corticosterone levels. Experiment 2 revealed that, independent of body weight, EE-and to a lesser extent, EEc-significantly accelerated F1 sexual maturation and incisors eruption. No differences were observed in F1 female fertility. In F1 males, mild but significant alterations in sperm quality were recorded, though these were insufficient to affect fertility. Worsening in sperm quality was possibly secondary to the significantly increased anxiety and aggressiveness observed in EE males, despite no differences in plasma corticosterone. In conclusion, basic EE accelerated postnatal development in mice, which could, in the long term, improve facility productivity.