Association between management practices, dairy herd characteristics, and somatic cell count of bulk tank milk.

Objective: To determine whether particular dairy management practices and herd characteristics were associated with somatic cell count (SCC) of bulk tank milk.
Design: Analysis of records.
Sample Population: Milk samples collected from 59,435 cows housed in 843 dairy herds between March 1992 and June 1994.
Procedure: Results of bacterial culture of milk samples and data on farm housing, sanitation, milking system, and management were collected. Multiple regression analysis was used to determine sources of variation in bulk tank milk SCC among herds.
Results: Prevalence of Streptococcus agalactiae and Staphylococcus aureus mastitis was associated with bulk tank milk SCC. In herds free of S agalactiae mastitis, prevalence of S aureus and Corynebacterium bovis mastitis were important. For herds without S agalactiae mastitis, use of sawdust bedding was associated with a decrease in SCC and a dirty loose housing area was associated with an increase. Increased milk production, repeated mastitis control visits, and use of particular predip compounds were significantly associated with reduced SCC in all herds, regardless of whether any cows in the herd had S agalactiae mastitis. In herds with S agalactiae mastitis, use of iodine (certain concentrations), chlorhexidine, peroxide, or sodium chlorite-lactic acid as a predip was associated with a decrease in SCC. Only use of sodium chlorite-lactic acid predip was significantly associated with a decrease in SCC in herds without S agalactiae mastitis.
Clinical Implications: Important factors associated with bulk tank milk SCC were prevalence of S agalactiae and S aureus mastitis, careful application of particular predip compounds, avoiding a dirty loose housing area, and use of a service to regularly monitor prevalence of mastitis in the herd.