Characterization of Biodefense Factors in the Bovine Mammary Gland Secretions and their Variation during the Periparturient Periods

Mammary gland secretions (MGS) of dairy cows at different lactating stages were studied for somatic cell (SC) counts (SCC), concentrations of bioactive proteins secreted from SC such as lactoferrin (Lf), α-1 acid glycoprotein (α-lAG), and fibronectin (FN), and for immunoglobulin subclasses of IgGl and IgG2. The SCC were low during the lactation period, but increased after the drying off started. Accompanying the increase in SCC, Lf increased and reached a maximum at early stage of drying off. Concentrations of α-1 AG and FN also increased and reached a maximum at middle stage of drying off. IgG1, which was consisted of a major Ig population in the MGS during the lactation period, increased further in the drying off and resulted in a high IgG1/lgG2 ratio with a maximum of 60-70 at latter stage of drying off when the colostrum was accumulated. These results suggest that the infiltration of SC and rapid production and accumulation of their bioactive secretory proteins in the MGS may be required for the transfer of mammary gland from the secretory phase to the drying off, and also help the accumulation of colostrum in the mammary gland preceding the parturition.