Milk composition in the North American opossum (Didelphis virginiana)

The composition of milk samples collected from captive opossums ( Didelphis virginiana ) was determined at various intervals during lactation. The milk solids increased from 9% at week one to a maximum of 34% at 11 weeks post-partum. There were changes in the relative proportions of protein, lipid and carbohydrate at different stages of lactation. Lipid represented the greatest fraction of the solids except for a period at mid-lactation when there was a peak in protein concentration. The concentrations of sodium, potassium and magnesium were relatively constant, 41 ± 4, 35 ± 11 and 9.2 ± 1.6 mmol respectively, although calcium increased from 13 ± 5 mmol at week one to a peak of 112 ± 35 mmol at 9 weeks.