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Milk samples were collected from 108,312 dairy cows during 1601 farm visits made between January 1991 and June 1995. The herd visits were made by personnel from the Central Laboratory of the Quality Milk Promotion Services at Cornell University (Ithaca, NY) to farms located in central New York and northern Pennsylvania. Dairy Herd Improvement Association records were available for 32,978 cows in 327 herds. Intramammary infections, as defined by positive milk cultures, were present in 48.5% of all cows and in 36.3% of cows in herds enrolled in the Dairy Herd Improvement Association. Over 75% of the intramammary infections were caused by Streptococcus agalactiae, Streptococcus spp. other than Strep. agalactiae, Staphylococcus aureus, and coagulase-negative staphylococci. Mean days in milk at the time of diagnosis, linear score of the somatic cell count, cost of milk loss per lactation, and milk production effects were calculated for 24 etiologic agents of bovine mastitis.

Objective: To determine whether particular dairy management practices and herd characteristics were associated with somatic cell count (SCC) of bulk tank milk., Design: Analysis of records., Sample Population: Milk samples collected from 59,435 cows housed in 843 dairy herds between March 1992 and June 1994., Procedure: Results of bacterial culture of milk samples and data on farm housing, sanitation, milking system, and management were collected. Multiple regression analysis was used to determine sources of variation in bulk tank milk SCC among herds., Results: Prevalence of Streptococcus agalactiae and Staphylococcus aureus mastitis was associated with bulk tank milk SCC. In herds free of S agalactiae mastitis, prevalence of S aureus and Corynebacterium bovis mastitis were important. For herds without S agalactiae mastitis, use of sawdust bedding was associated with a decrease in SCC and a dirty loose housing area was associated with an increase. Increased milk production, repeated mastitis control visits, and use of particular predip compounds were significantly associated with reduced SCC in all herds, regardless of whether any cows in the herd had S agalactiae mastitis. In herds with S agalactiae mastitis, use of iodine (certain concentrations), chlorhexidine, peroxide, or sodium chlorite-lactic acid as a predip was associated with a decrease in SCC. Only use of sodium chlorite-lactic acid predip was significantly associated with a decrease in SCC in herds without S agalactiae mastitis., Clinical Implications: Important factors associated with bulk tank milk SCC were prevalence of S agalactiae and S aureus mastitis, careful application of particular predip compounds, avoiding a dirty loose housing area, and use of a service to regularly monitor prevalence of mastitis in the herd.

Objective: To evaluate efficacy of florfenicol treatment for bovine mastitis caused by Streptococcus agalactiae, Staphylococcus aureus nonagalactiae streptococci, coagulase-negative staphylococci, Escherichia coli, Klebsiella sp, and others., Design: Double blind study with cases randomly assigned to 1 of 2 treatment groups., Sample Population: 861 cows/10 commercial dairy farms., Procedure: Experimental (750 mg of florfenicol) or control (200 mg of cloxacillin) treatment was administered by intramammary infusion every 12 hours for 3 treatment to all cases. Treatments were randomly assigned identified only by numerical labels. To retain blinding, the longer withdrawal time was adhered to for all cases. Cases remained in the study only if there was no other treatment. Quarter samples were recultured 14, 21, and 28 days later. If all samples after day 1 were culture negative, the case was defined as cured. If only 1 of the follow-up results was positive, the case was considered cured if the day-28 somatic cell count was < 300,000/ ml. Failure of treatment was defined as 2 or more culture positive follow-up samples., Results: Florfenicol and cloxacillin did not differ significantly in efficacy versus clinical (n = 85) or subclinical (n = 71) bovine mastitis, or for any etiologic agent (X2). Overall cure rates for mastitis were: Str agalactiae, 5 of 8 (63%); Sta aureus, 5 of 54 (9%); Streptococcus sp, 16 of 35 (46%); Staphylococcus sp, 7 of 33 (21%); E coli, 5 of 11 (46%); Klebsiella sp, 3 of 6 (50%); others, 1 of 9 (11%); and all cases, 42 of 156 (27%)., Conclusions: Florfenicol did not offer any advantage over cloxacillin in efficacy against bovine mastitis. Overall cure rates were low. As with most mastitis treatment regimens poor efficacy may be partly attributable to the short duration of treatment.