Relation of milk production loss to milk somatic cell count

Milk production loss was studied in relation to increased somatic cell coun t (SCC). Available data were weekly test-day milk yields and SCC (in 1,000 cells/ml), and mastitis incidences. In total, 18,131 records from 274 cows were used. Production loss was determined for test-day kg milk, kg protein, and kg energy-corrected milk. Least-squares analysis of variance was used to estimate the direct effect of Log(10)(SCC) on production. The recorded m easures of production were first corrected for fixed effects, with adjustme nt factors estimated from a healthy data-set. The average daily milk yield was 19.7 kg/day in first lactation and 22.0 in later lactations. The geometric mean of SCC was 63.1 in first lactation an d 107.2 in later lactations. The incidence of clinical mastitis treated by a veterinarian was 19.8% of the lactations-at-risk. Linear relationships we re found between the production parameters and Log(10)(SCC). Quadratic and cubic effects were evaluated, but were found to contribute little to the ov erall fit of the models. The individual milk yield loss was 1.29 kg/day for each unit increase in Log(10)(SCC) for cows in first lactation. Milk yield decreased by 2.04 kg/day per unit Log(10)(SCC) for older cows. Correspondi ng values for protein yield were 0.042 and 0.067 kg/day for first and later lactations, respectively.