Genetic parameters of bovine serum immunoglobulins.

Radial immunodiffusion techniques were used to determine serum concentrations of immunoglobulins G1, G2, M, and A in 1,293 daughters of 282 Holstein-Friesian sires from 31 herds in southwestern Ontario, Canada. Mean serum immunoglobulin concentrations (mg/100 ml) were 2,163, 2,409, 531, and 107 for immunoglobulins G1, G2, M, and A, respectively. Herd effects were significant for all four immunoglobulin isotypes. Age of cow effects were significant for immunoglobulins G1 and G2 only. Both immunoglobulins G1 and G2 increased with age, but the rate of increase of G2 was twice that of G1. Stage of lactation had a significant effect on G2 and M. Immunoglobulin G2 was highest in the first 200 d post-calving and immunoglobulin M was highest late in lactation and during the dry period. Paternal half-sib heritabilities for immunoglobulins G1, G2, M, and A were .10, .10, .09, and .14, respectively. Genetic correlations among the four immunoglobulin isotypes ranged from .49 to 1.02. Genetic correlations between immunoglobulin G2 and 305-d milk and fat yields were .36 and .13 and between immunoglobulin A and 305-d milk and fat yields were .37 and .63. Genetic correlations between immunoglobulin M and milk and fat production were negative (-.83 and -.34). Phenotypic correlations between immunoglobulin isotypes were low except for the correlation between immunoglobulins G1 and G2, which was .36.