Outcome of clinical mastitis in dairy heifers assessed by reexamination of cases one month after treatment.

Heifers that were treated for clinical mastitis prior to parturition or within 14 d postpartum were reexamined approximately 1 mo after treatment. Clinical examination of the heifers and microbiological examination of quarter milk samples were carried out on both occasions. Of the 1000 heifers included in the study, 10.9% were culled within 28 d after treatment. Udder damage caused by mastitis was the only or main reason for culling in 96% of those heifers. In comparison, 4.5% of nonmastitic heifers from the same herds were culled within 30 d postpartum. Twenty-five percent of those heifers that were not culled at d 28 after treatment had at least one nonfunctional quarter at that time. One thousand one hundred twenty-two quarters that were clinically affected at the time of treatment were reexamined; 22% were nonfunctional, 14% were still affected by clinical mastitis, 12% had subclinical mastitis, 5% had a latent infection with coagulase-positive staphylococci or Streptococcus dysgalactiae, and 46% were bacteriologically negative and had a normal cell count at the time of reexamination. High percentages of nonfunctional quarters were observed among those quarters that were infected with Arcanobacterium pyogenes or with coagulase-positive staphylococci at treatment. When all quarters that were clinically affected at treatment were considered, 40% of quarters were cured and were still in lactation at reexamination. Quarters infected with coagulase-negative staphylococci had a higher cure rate than quarters infected with other organisms. At reexamination, clinical signs of thelitis were observed in many of those quarters that were nonfunctional following the episode of clinical mastitis and also in 25% of lactating quarters in which clinical mastitis persisted.