Quality of Vermont bulk tank milk was first surveyed in 1985 as part of a statewide milk quality enhancement program. In a second survey conducted in 1990, bulk tank milk from 1,971 farms was sampled and tested for standard plate count, bacterial type and species distribution, and somatic cell count. Test results from 1,203 duplicate bulk tank milk samples were compared between five Vermont milk processors and the University of Vermont Quality Milk Research Laboratory. Arithmetic mean standard plate count conducted by processors was 2.3 × 104 CFU/ml in 1990 compared with 3.0 × 104 CFU/ml in 1985 (Geometric mean went from 1.3 × 104 CFU/ml in 1985 to 1.1 × 104 CFU/ml in 1990). Trypticase blood-esculin agar was used at the Quality Milk Research Laboratory to determine distribution of bacteria types and species. Comparison of results with a 1985 survey appeared to demonstrate a reduction in the percentage of farms with Streptococcus agalactiae from 47% to 32%. Frequency of other organisms increased with the majority being environmental organisms. Arithmetic mean total raw bacteria count on blood agar was 1.9 × 104 CFU/ml. Correlation between standard plate count and blood agar raw bacteria count was low. Arithmetic mean somatic cell count appeared to decline from 5.4 × 105 cells/ml in 1985 to 3.4 × 105 cells/ml in 1990 (Geometric mean went from 4.1 × 105 cells/ml in 1985 to 2.9 × 105 cells/ml in 1990). Correlation between somatic cell counts conducted by milk processors and the Quality Milk Research Laboratory was high.
1Department of Animal Science,
2Computer and Statistical Services.