Environmental streptococcal intramammary infections of the bovine mammary gland.

Characteristics of environmental streptococcal IMI were investigated over a 7-yr period for a herd in total confinement. A total of 374 new environmental streptococcal IMI was detected. Approximately 50.5% of IMI were new in the dry period, and 49.5% were new in lactation. The rate of new IMI was .00312 IMI/cow day during the dry period and .00054 IMI/cow day during lactation. The percentages of cows and quarters with an environmental streptococcal IMI present at calving were 10.6 and 3.2%, respectively. The percentage of heifers with an environmental streptococcal IMI at calving was similar to that for cows. The rate of new environmental streptococcal IMI was greater during the 1st mo of lactation than during the remainder of lactation. The rate of IMI during late lactation was higher for older cows than for either heifers or cows in second lactation. The rate of environmental streptococcal IMI during the dry period and during lactation was greatest during summer. The mean days of lactation that cows were infected for all IMI was 12.3 d. Approximately 41% of IMI had a duration of < 8 d. Stage of lactation, season of the year, and parity influenced the rate of new IMI.