Environmental and physiological factors affecting mastitis at drying off and postcalving.

Duplicate milk samples from udder quarters were collected from 3987 cows when the cows were dried off and again postcalving. Samples were cultured for staphylococcal, Streptococci agalactiae, other streptococci species, and coliform organisms. Cows were treated with one of five dry cow therapy drugs or left as untreated controls after collection of samples at dry off. Cows treated with dry cow therapy drugs had more quarters cured during the dry period than did untreated control cows for all organisms considered. A program of dry cow treatment plus teat dipping was superior to dry cow treatment only, teat dipping only, or neither. Cows were more vulnerable to mastitis infections with increasing age. Month of year of drying off affected mastitis infection, although trends were erratic and varied by organism. Mastitis infections at dry off under different herd management systems of type of milking equipment, type of milking facility, and type of housing were dependent on the organism. Management systems had little influence on mastitis infections postcalving. Higher producing cows had fewer mastitis infections when dried off, but milk production the previous lactation had little influence on mastitis infections postcalving.