Relationship between milk production and somatic cell count in dairy cows in East Gippsland

The analysis of records for 75,821 herd tests on 23,700 cows in the Macalister Irrigation District of East Gippsland, using a model that also included stage of lactation, herd and cow effects, found a strong relationship between somatic cell count and milk production. Unit increases in the natural logarithm of the somatic cell count were associated with decreases in production of up to 2.6% in the range 54,598 to 403,429 cells per mL. This is equivalent to a decrease of 1.9% for a doubling of cell count from 100,000 to 200,000 cells per mL. Subclinical mastitis was assessed to be a significant source of loss in milk production in the study area.