Comparison of methods for obtaining milk samples from well-nourished and malnourished rats

Milk samples from well-nourished and malnourished rats were obtained at day 14 of lactation by a standard pumping procedure and an alternative procedure in which the pups were allowed to nurse and milk was collected from their stomachs. Samples obtained by the 2 methods from well-nourished rats did not differ in their concentrations of water, protein, and fat. However, among malnourished rats, pumped samples had significantly higher protein and fat concentrations than nursed samples because they were excessively dehydrated. For both dietary groups, a consistently larger proportion of the available milk was obtained by the nursing method. The results suggest that the nursing method is superior to pumping for obtaining milk samples when rats varying in nutritional status are to be compared.