Abstract: A method for lowering somatic cell count in the milk of a lactating ruminant is disclosed. IgY antibodies are first obtained from the egg of a hen which has been actively immunized against one or more mastitis-causing pathogenic organisms by injection with an immunogen containing immunogenic determinants specific to elicit such antibodies. The immunogenic determinant may comprise only a specific portion of the pathogenic organism, e.g., the fimbria of a piliated bacterium. The IgY antibodies are then administered orally to a ruminant in which it is desired to lower milk somatic cell count. Antibody administration may occur during a ruminant's dry period as well as during lactation. In a preferred embodiment, the antigen used in immunization of the hen comprises one or more of Staphylococcus aureus and Streptococcus agalactiae. The method of this invention has been shown to be efficacious in lowering somatic cell count in dairy cattle.