Development and validation of a nephelometric immunoassay for IgG1 in milk

A nephelometric immunoassay, with a detection range of 0.3 to 5 g IgG(1)/l, was developed for the determination of immunoglobulin in bovine milk. The assay exhibited no significant cross-reactivity with alpha(S1)-casein, alpha(S2)-casein, beta-casein, kappa-casein or beta-lactoglobulin and 39% cross-reactivity with IgG(2). The nephelometric assay was compared with ELISA and RID (24 h and 48 h incubations) assays using 105 duplicate milk samples covering IgG(1) values ranging from 0.45 to 1.8 g(1). The results obtained from all assays showed good agreement, with the exception of those obtained by the RID assay (24 h incubation) which gave tower results in samples containing more than 1.2 g IgG(1)/l. It was concluded that the nephelometric assay is a reliable, rapid and convenient method suitable for the quantification of IgG(1) in milk. The assay can be configured for routine high-throughput milk quality assurance for IgG(1) in dairy laboratories.