Haplotypes of the FCGRT gene, coding for the MHC Class I α-chain of FcRn, are associated with serum concentrations of IgG in neonatal beef calves [141] and associated with IgG concentrations in colostrum of dairy cows [142] . Haplotypes of the β2-microglobulin gene (β2M) also are associated with serum IgG concentrations in newborn calves [143] . In estimating mass transfer of IgG1 into colostrum in dairy cattle, 10% of cows had mass transfer greater than one standard deviation above the mean, perhaps indicating a genetic or hormonal regulation of the variance of transport [144] . Clearly there is opportunity for genetic manipulation of IgG transport in the mammary gland to enhance the concentrations of immunoglobulins in colostrum and milk. However, it should be remembered that serum IgG concentrations in the periparturient cow are already decreased as a result of the extensive IgG transport into the colostrum [145] , and as indicated above, the cow is in an immunosuppressed state during the peripartum period [88, 89] .