BACTERIAL-GROWTH, INFLAMMATORY CYTOKINE PRODUCTION, AND NEUTROPHIL RECRUITMENT DURING COLIFORM MASTITIS IN COWS WITHIN 10 DAYS AFTER CALVING, COMPARED WITH COWS AT MIDLACTATION

Objective-To define causes of increased susceptibility to coliform mas titis after parturition. Animals-12 healthy Holstein cows assigned to 2 groups. Group-1 cows (n = 6) had carved between 6 and 10 days earlie r. Group-2 cows (n = 6) were in midlactation. Procedure-Cows from each group were paired and challenge exposed with Escherichia coil in 1 ma mmary gland. Mastitis severity was determined by bacterial concentrati on in milk, pyrexia, and milk production. Measures of host defense wer e neutrophil chemotaxis, adhesion molecule expression, leukocyte recru itment, and cytokine production. Results-After challenge exposure, gro up-1 cows had more rapid E coil growth, higher peak bacterial concentr ation, and higher fever. Leukocyte recruitment was poor in 1 group-1 c ow that had peracute mastitis. In contrast, leukocyte recruitment in 5 other group-1 cows began sooner than that in group-2 cows. In these g roup-1 cows, prechallenge-exposure milk somatic cell counts (SCC) were significantly lower than those in group-2 cows. Prechallenge-exposure SCC were correlated to stimulated CD18 expression (R(2) = 0.79), and both measures correlated inversely with bacterial growth rate (R(2) = -0.75). Values for tumor necrosis factor alpha, interleukin 1, and int erleukin 8 in group-1 cows after challenge exposure were greater than or equal to those in group-2 cows. Conclusions-Weak leukocyte recruitm ent to the mammary gland is associated with increased severity of coli form mastitis. Impaired production of cytokines measured is not a caus e of increased susceptibility to coliform mastitis in early lactation. Clinical Relevance-Low milk SCC after calving may increase susceptibi lity to severe coliform mastitis.