Cost of mastitis and its prevention in four dairy cattle herds on St Croix, US Virgin Islands

Nonclinical mastitis in the dairy herds on St Croix, US Virgin Islands, represents a prevalent (97%) and severe problem (44% of quarters had California Mastitis Test results of 2 or 3). Streptococcus agalactiae (26%) and Staphylococcus aureus (22%) were the most prevalent pathogens. More than half (54%) of all organisms isolated and tested for resistance were resistant to ampicillin and benzyl penicillin; 29% were resistant to trimethoprim/sulfadiazine. Estimates of the loss of milk production suggested that there was a loss of 4.40 to 13.33 lb/cow/day. The yearly economic cost of prevention was estimated for each cow ($22.07); yearly income loss attributable to mastitis was estimated to be from $339 to $1,022/cow/yr. Suggestions for the prevention and control of mastitis are included.