The effect of oral immunization on the population of lymphocytes migrating to the mammary gland of the sow.

Sows were immunized orally with live Escherichia coli according to various immunization schedules. Six pregnant gilts were used; 4 immunized at various intervals during the last month of gestation, 1 control immunized after parturition following suppression of lactation by weaning and 1 non-immunized control. The effect of oral vaccination on cell populations from lymphoid organs was studied.