Bacterial and Somatic Cell Counts in Bulk Tank Milk from Nine Well Managed Herds1

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Abstract
Factors associated with bulk tank milk bacterial and somatic cell counts were investigated for one year on nine well managed dairies. Geometric mean total bacterial count among dairies was 4.4 × 103 colony cfu/ml. Geometric mean bulk tank milk somatic cell counts among herds was 265 × 103ml. Bacterial counts in bulk tank milk were correlated with rates of coliform and environmental streptococcal clinical mastitis cases. Rates of total clinical cases were also correlated with bulk tank milk somatic cell counts. Correlations were measured among bulk tank milk bacterial counts and gram-negative bacterial, coliform, Klebsiella species, and streptococcal counts in materials used to bed lactating cows. Total bacterial and staphylococcal bulk tank milk counts increased when synthetic rubber liners were used greater than 800 quarter milkings. Correlations measured indicated that monitoring bulk tank milk may be an effective means of detecting management changes in herds with low bacterial and milk somatic cell counts.