Reconstitution of mastitic milk by adding blood plasma and leukocytes into low cell count milk

Milk from inflamed quarters is high in somatic cells, proteolytic activity and lysosomal enzyme activity. Addition of homologous blood plasma and leukocytes into low cell count milk did not increase the plasmin activity, total proteolytic activity or N-acetyl-beta-D-glucosaminidase (NAGase) as anticipated, even if the reconstituted milk samples were stimulated by endotoxin or opsonized zymosan. Addition of urokinase activated the latent proteolytic system in plasma-supplemented milk. The reactive sulfhydryls in milk samples with different treatments decreased significantly after incubation, indicating the presence of an oxidative mechanism in milk (eg, sulfhydryl oxidase). The high background resazurin reduction of fresh milk might be due, in part, to the cellular activity of somatic cells. This study indicates that a more complex system including inflammatory mediators and complex cellular interactions is required for expression of plasmin-activator activity and for full activation of the proteolytic and lysosomal enzymes in mastitic milk.