Production and Turnover of IgG1 and IgG2 Immunoglobulins in the Bovine around Parturition

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Abstract
Production rates (entry rate into blood plasma) and other metabolic parameters for the IgG1 [immunoglobulin G1] and IgG2 subclasses in mammary secretions (ratio of about 7:1) were determined in cows around the time of parturition by single-injection and continuous-infusion isotope-dilution techniques. Four cows were given a single dose of 150-200 .mu.Ci of 125I labeled IgG1 and 100-250 .mu.Ci of 131I labeled IgG2 at 1-2 wk before parturition. Four cows, including 2 of the above, were infused continuously with constant amounts of the labeled Ig starting at 11-4 days before parturition. All cows were maintained until 4-6 days after parturition for monitoring the specific activities of 125I labeled IgG1 and 131I labeled IgG2 in the plasma and mammary secretions. Maximum entry rates of IgG1 and IgG2 were 1-3 days prepartum with means of 125 and 60 g/500 kg body wt per day. The exchangeable pool means for IgG1 and IgG2 were 619 and 643 g/500 kg body weight, and both Ig were divided almost equally between the intra- and extravascular pools. A greatly increased production and a shortened half-life or greater turnover for plasma IgG1 occurs around the time of parturition which can account for the large accumulation of IgG1 in colostrum.