An Efficient Single-Person Technique for Milk Sampling from Laboratory Mice

Rodent models have been widely used in biology since the early 20th century to study basic physiology and biochemical mechanisms. In lactation and neonatal development research, there is a need to sample milk to determine the composition and how milk may be affected by experimental manipulations, thereby impacting newborn development. Collecting biofluids in sufficient amounts from small rodents can be difficult. Several studies have demonstrated different techniques to obtain milk from mice. However, these techniques often require at least two trained personnel, which may be challenging in some cases.  Here, we demonstrate a modified milk sampling technique based on a method published in 2009. With this affordable and easy-to-assemble method, one trained person can routinely obtain 0.1-0.5 mL of milk from a dam under anesthesia in less than 10 min. Using this method, we collected sufficient milk on post-delivery day 2 (PD2) and post-delivery day 10 (PD10). We measured milk macronutrient components and compared them with the existing literature to validate our collection method.  We recorded that on PD2, milk protein averaged at 70.1 ± 5.2 g/L, milk fat was 174.4 ± 7.1 g/L, and milk lactose was 12.3 ± 0.6 g/L. On PD10, while milk lactose and protein remained at similar concentrations as on PD2, milk fat was significantly higher (224.4 ± 17.1 g/L). We also observed that the relative abundance of individual milk proteins varied between PD2 and PD10. More specifically, αS1-casein and whey acidic protein were higher, while β-casein was lower at PD10 compared with PD2. Overall, we demonstrate an efficient single-person technique for milk sampling from mice using a device that can easily be assembled with commonly used laboratory equipment.