Use of Laboratory Mice to Study Genetic Relationships Among Milk Yield and Number of Somatic Cells

Preliminary results of bidirectional selection for increased and decreased somatic cell counts in milk of laboratory mice were used to assess the usefulness of the laboratory mouse as a pilot organism for the study of yield and somatic cell count relationships in dairy cattle. Procedures developed permit relatively rapid and accurate determination of somatic cell counts in milk of mice. Concentration of somatic cells was three to four times greater in mice than in dairy cows, but counts were distributed similarly. A large effect for stage of lactation existed with high counts in late lactation. Within lactation, repeatability of somatic cell counts and relationships between somatic cell counts and milk yield were similar to those reported for dairy cattle. Heritability of lactation average somatic cell count (3 sample d, log base 2, adjusted for stage of lactation) was .24, indicating lines genetically divergent for somatic cell count can be developed.