Physiological and Pathological Factors Influencing Bovine Immunoglobulin G2 Concentration in Milk

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Abstract
Bovine IgG2 concentration was determined by radial immunodiffusion in 355 milk samples of uninfected quarters, 101 milk samples of infected quarters, and 118 blood serum samples from 42 Holstein-Friesian cows taken at 30, 150, and 270 d. Concentration of IgG2 in blood serum (11.3 mg/ml) was highest at the beginning of lactation (30 d). Immunoglobulin G2 concentration in milk (16.81 .mu.g/ml) from cows with uninfected quarters was not affected by quarter location but was correlated with IgG2 concentration in blood serum (.30; P < .001). The IgG2 concentration in milk was lower in midlactation (150 d: 14.81 .mu.g/ml) and in the two first lactations. Immunoglobulin G2 concentration in milk was correlated with SCC. Quarter infection by Corynebacterium bovis or major pathogens increased IgG2 concentration up to 47.9 .mu.g/ml for Staphylococcus aureus. Only S. aureus influenced IgG2 concentration in blood serum. Correlation between IgG2 content and SCC in milk decreased when quarters were infected, regardless of bacterial species.