Validation in well- and poorly nourished rats of a method to collect milk for compositional analysis

Abstract

The nursing method of milk collection is a procedure in which milk is collected from the stomachs of rat pups after they are allowed to suckle. When dams are undernourished, higher volumes can be obtained this way than by expressing milk from the dam's nipple. However, composition of the milk is changed by being in the pups' stomachs. To validate the nursing method of milk collection for use among pups differing in nutritional status, we determined whether this change in composition is the same in well- and poorly nourished pups. Milk was collected from well-nourished dams, pooled, and its macronutrient composition determined. This milk was fed by garage to 14-d- old pups of rat dams given free access to diet AIN-93G(TM) (control) or restricted to 50% of the average intake of control rats (food-restricted). Their stomach contents were collected 30 min later. There were no significant differences between the pups of control and food-restricted dams in the composition of the milk curd recovered from the pups' stomachs. As expected, the pups' stomach contents had significantly lower water, fat and lactose concentrations than the pooled milk fed. Thus, the nursing method of milk collection does not provide a sample suitable for the determination of the absolute composition of the milk fed. Inasmuch as pup undernutrition does not differentially affect the compositional changes that occur when milk is in the pups' stomachs, the nursing method of milk collection provides a valid comparison of the relative composition of the milk consumed for pups who differ in nutritional status.