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Milk samples from 45 quarters containing mastitis pathogens were collected from lactating cows to determine the viability of those pathogens after freezing. An initial bacteria count was conducted, and samples were divided into 2-ml portions and frozen. Weekly bacteria counts were conducted for 6 wk. Viability after freezing was determined on five isolates of nine bacterial species: Staphylococcus aureus, Staphylococcus hyicus, Staphylococcus chromogenes, Staphylococcus xylosus, Streptococcus agalactiae, Streptococcus dysgalactiae, Streptococcus uberis, Corynebacterium bovis, and Escherichia coli. Bacteria counts were converted to logarithm base 10, and analysis of variance was conducted to determine alterations in viability over the 6-wk period. Freezing of quarter milk samples for 6 wk did not affect viability of any of these pathogens.

A powdered teat dip designed for winter usage was evaluated for bacteriological efficacy and teat conditioning qualities. A positive control, natural exposure field trial was conducted for 3 mo on 509 lactating cows. Two sets of cows, primiparous and multiparous, were used. The trial compared efficacy of a powdered teat dip with a teat dip of 1% iodine plus 10% glycerin. Bacteriological efficacy among primiparous cows was equivalent for all major mastitis pathogens, environmental pathogens, and streptococci other than Streptococcus agalactiae. Efficacy was not equivalent against coagulase-negative staphylococci and all mastitis pathogens. Results suggested that the positive control product was more efficacious. Among multiparous cows, efficacy was equivalent against environmental mastitis pathogens and bacteriologically negative, clinical mastitis. The products were not equivalent against Staphylococcus aureus, coagulase-negative staphylococci, or all major mastitis pathogens, once again suggesting that the positive control product was more efficacious. Data indicated that germicidal activity of the powdered dip was not sufficient to reduce the incidence of new IMI caused by contagious or minor pathogens normally associated with teat skin. Application of a powdered postmilking teat dip during 3 winter mo in Idaho resulted in improved teat end condition among primiparous and multiparous dairy cows. Teat skin condition improved among primiparous but not among multiparous cows.

The ability of verocytotoxin‐producing Escherichia coli (VTEC) O157: H7 to enter selected human (RPMI‐4788 and HeLa) and bovine (MAC‐T, mammary secretory; MDBK, kidney) epithelial cell lines was evaluated. All VTEC evaluated efficiently entered RPMI‐4788 and MAC‐T cell lines. VTEC entered MDBK cells at approximately 4% of MAC‐T cells. VTEC were not able to invade HeLa cells. Presence of plasmid had no influence on efficiency of entry, nor did production of shiga‐like toxin (SLT I or SLT II). Internalization required microfilaments, but not microtubules. Two types of adherence, localized and diffuse, were exhibited depending on isolate and cell line evaluated. Ability of VTEC to invade bovine mammary epithelial cells may be important in pathogenesis in the bovine, may indicate a route by which raw milk may potentially become contaminated, and may provide a reservoir of bacteria for the contamination of workers, equipment and carcass at time of slaughter.

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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.

A natural exposure field trial a with positive control was conducted to evaluate bacteriological efficacy and teat conditioning qualities of an experimental postmilking teat dip. An experimental 1% iodine postmilking teat sanitizer with a 10% emollient system was compared with a 1% iodine plus 10% glycerin teat sanitizer. Efficacy of the two sanitizers was equivalent for all new IMI, major pathogens, and environmental pathogens. The products were not equivalent for efficacy against coliforms and coagulase-negative staphylococci. Fewer coliform IMI were diagnosed in the control group than in the treatment group. Differences were determined for efficacy against coagulase-negative staphylococci in favor of the treatment product. The products were equivalent for all clinical mastitis, including previously existing IMI that became clinical. The products were not equivalent for all or new clinical IMI with major pathogens, all environmental pathogens, or coliforms. Fewer infections were diagnosed in the control group than in the treatment group. Teat end and teat skin conditions improved with the use of the triple emollient, postmilking teat sanitizer under the winter conditions experienced during this field trial.