Background

The common use of neonatal mice in developmental studies can result in maternal rejection (or even, in some circumstances, cannibalization) after experimental or genetic manipulations. In other situations, neonatal mice may be unable to suckle on their own; for example, anosmic mutant mice face severe difficulties in their suckling behavior (Brunet et al., 1996; Fujimoto, et al., 2023). These difficulties make it hard to determine whether altered development is due to the manipulation or simply due to a lack of maternal feeding.

In these cases, it is often necessary to hand rear the pups to prevent any difficulties. Successful hand rearing is dependent on more than simply delivering sufficient nutrients. For example, nesting conditions can have an influence on thermal stress and postnatal development (Gaskill et al., 2012; Mason et al., 2018). However, the majority of previous attempts have focused on nutrient delivery. To this end, a variety of techniques have been employed, such as force feeding with a syringe (Pleasants, 1959; Hoshiba, 2004) or directly adding nutrients to the stomach via a gavage (Messer et al., 1969; Hall, 1975). However, these methods were either only partially effective or technically difficult, which resulted in unreliable results or a low success rate. Additionally, varying the type of milk only produced worse results (Smart et al., 1984; Tonkiss et al., 1987).

Could a combination of improving the environmental conditions, feeding techniques, and neonatal care result in more effective and reliable growth of pups? There is a wide array of non-academic advice on how to rear mice (Creek Valley Critters, https://www.youtube.com/user/CreekValleyCritters), and we sought to harness this knowledge and apply it to biological research (Fujimoto et al., 2023). We discovered that the key features for successful growth were warm temperatures, regular feeding every two hours, and belly massages to avoid bloating. While this technique is manually very intensive, it produces pups that are healthy, and it does not require technically difficult procedures.