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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.