The WSW method is based on weigh of piglets immediately before and after nursing by the sow.
The WSW sequence is repeated several time during a day. And the sum of the weight gains of the piglet is taken as the amount of milk consumed. Between nursing bouts the piglets are nit allowed access to the sow, and the time interval between nursing is determined by the investigator, not by the piglets or sow. This method suffers several disadvantages. First, it disrupts the social interaction of the sow and litter, and impose an arbitrary nursing interval.