In Switzerland, 64% of experimental animals are mice, amounting to more than 369 436 mice used for experimental purposed in 2021 (Bundesamt für Lebensmittelsicherheit und Veterinärwesen BLV, 2021). We assume that these mice are born from healthy breeders, but we do not have solid evidence to support this notion. The current breeding methods are structured to maximise the reproductive success and can thus result in the breeding dam experiencing multiple cycles of concurrent pregnancy and lactation. We presume that concurrent pregnancy and lactation leads to some metabolic and physical strain on the dam, yet whether it affects the wellbeing of the dam is poorly understood.

The aim of this study was to determine whether the current breeding methods reduce the welfare of the mouse dams. The physiological health and behaviour of the dams were analysed after 1, 2, or 4 pregnancy cycles. Dam body weight and food intake were monitored during the entire experiment. Pup retrieval tests were conducted on postpartum day three, six, and nine. Finally, immunohistochemistry of dam brains was performed to analyse leptin sensitivity and quantify oxytocin expression in the hypothalamus.

An effect of number of pregnancy cycles was observed in the body weight and food intake parameters. Multiparous dams were significantly heavier than primiparous dams and female virgins and had a lower food intake than primiparous dams. We found that maternal behaviour during pup retrieval test is more influenced by strain than by reproductive experience.

Immunostaining of mouse dam hypothalamus demonstrated the presence of neurons expressing oxytocin and leptin-responsiveness, yet further analysis is required to draw conclusions about the impact of concurrent pregnancy and lactation on these measures.