How does housing quality affect maternal investment and reproduction?

Abstract

Poor housing is linked to reproductive failure in captive mammals, but the mechanisms are rarely tested. To understand the mechanism behind it, we used DBA/2 mice as models and in conventional housing (CH) and well-resourced housing (WR) across three cohorts (N = 36 sister-pair cages; 6 CH and 6 WR per Cohort). We tested two mutually non-exclusive mechanisms: the energy hypothesis (low maternal body condition, measured as BMI, impairs reproduction) and the stereotypic behaviour (SB) hypothesis (SB competes with reproduction and maternal care regardless of body condition). Housing affected maternal care: WR dams built better nests (p = 0.002), nursed more (p = 0.018) and nursed for more days before weaning (p = 0.023), and their pups tended to be heavier at PND 28 (14.2 vs 12.5 g, p = 0.06). Unexpectedly, all CH dams (7/7) retrieved displaced pups, but no WR dams did (0/8), likely reflecting how the test cage was perceived. But housing did not affect mating, pregnancy, litter size, pup survival or pup weight up to postnatal day (PND) 21. CH females performed about 9 times more SB than WR females before mating, and the difference persisted through lactation. BMI did not differ by housing, so the energy hypothesis was not supported. Adding SB to models weakened housing effects on nest quality and nursing, but SB itself did not significantly predict any outcome. Here, we found that housing quality mainly shapes how dams care for pups during lactation but not their capacity to breed. SB may play a partial role, but that needs better-powered testing. This study supports improving housing for captive breeding programmes now, even though the mechanism remains unknown.