Physiological and pathological factors influencing bovine immunoglobulin G2 concentration in milk.

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 micrograms/ml) from cows with uninfected quarters was not affected by quarter location but was correlated with IgG2 concentration in blood serum (.30; P less than .001). The IgG2 concentration in milk was lower in midlactation (150 d: 14.81 micrograms/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 micrograms/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.