All samples are stored at -80°C in 1 mL aliquots and are accompanied by maternal demographic information and milk macronutrient analysis. A particularly valuable subset of 500 samples (Southern Cross) has been extensively characterised beyond macronutrient composition to include hormones (leptin and adiponectin), immune proteins, proteomics, and metabolomics. With known composition across multiple analytes, these 500 samples provide a readily available resource for optimising existing assays and developing new ones, removing the time and burden of primary sample collection.