Changes in concentrations of insulin-like growth factor 1, insulin and growth hormone in bovine mammary gland secretion ante and post partum.

Concentrations of insulin-like growth factor 1 (IGF-1), insulin and growth hormone were measured in the secretion of the bovine mammary gland from day 70 ante partum until 6 d post partum. Highest levels were found during the last 2 weeks ante partum followed by a rapid decrease during the first milkings post partum. The association of IGF-1 with its binding proteins in milk was analysed and striking differences were found in the distribution of bound and free IGF-1. IGF-1 appeared mainly in the bound form (91%) at days 40-2 ante partum. Free IGF-1 preponderated in the first milkings post partum (73%) and changed again to about 85% in the bound form after day 4 post partum. A slightly acidic pH (6.3) of the secretion was correlated with high amounts of free IGF-1. Gel filtration experiments revealed a possible pH-dependent mechanism for the binding of IGF-1 to its binding proteins in milk.