Immunoglobulin isotype concentrations in milk as affected by stage of lactation and parity.

Quarter milk samples were collected during lactation and analyzed for immunoglobulins from 32 first and 16 third lactation Holstein cows that were equally distributed progeny of sires selected for yield or merit. Variance component estimates indicated large variation for cow, quarter within cow, and stage of lactation. All immunoglobulin isotype concentrations were lowest at wk 21. Significant differences between first and third lactation cows were observed for milk immunoglobulin A (.012 and .018 mg/ml) and immunoglobulin M (.074 and .101 mg/ml). Quarters with cell counts above 1 X 10(6) cells/ml had higher concentrations of immunoglobulin G1, (.619 vs. .394 mg/ml) immunoglobulin G2 (.103 vs. .063 mg/ml), immunoglobulin A (.028 vs. .014 mg/ml), and immunoglobulin M (.117 vs. .087 mg/ml). There were no significant differences in immunoglobulin isotype concentrations due to genetic group (yield or merit), suggesting that selection for milk production has no significant effect on immunoglobulin concentration in milk. Degree of parity, however, must be considered when comparing immunoglobulin A and immunoglobulin M concentrations in milk.