Protease Inhibitor Levels in Porcine Mammary Secretions

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Abstract
The total trypsin inhibiting capacity (TIC), and the content of the individual protease inhibitors, both the specific colostrum protease inhibitor (SCTI) and the serum-type inhibitors, i.e., α2-macroglobulin f and s, inter-α-trypsin inhibitor, α2-antitrypsin and α1 protease inhibitor, were quantified in porcine mammary secretions throughout lactation using immunoprecipitation methods. In addition, albumin, of serum origin, and β-lactoglobulin, a milk-specific protein, were quantified and used as references. In presuckled colostrum, high levels of TIC, SCTI, albumin and β-lactoglobulin were found, while the serum-type inhibitors appeared in amounts related to their molecular weights ranging from 3–6% of the adult serum levels for the macroglobulins to 42% for αi-protease inhibitor. These parameters all decreased during lactation. The levels of TIC and SCTI especially decreased during the first days of lactation, and SCTI disappeared from milk after 5–7 days. Mature milk showed low TIC levels, about 0.1 IU/ml, which originated from the low amounts of the serum-type inhibitors (1–4% of the adult serum level). The levels of both α2-macroglobulin f and s decreased less than albumin did in sow milk, while the other inhibitors decreased more or on the same order as albumin. A considerable variation in the amounts of the protease inhibitors between individuals and also between different teat secretions of the same sow, especially in colostrum, was evident. The possible physiological functions of the protease inhibitors in the mammary gland of the sow and in the gastrointestinal tract of her nursing offspring are discussed.