Changes in insulin-like growth factor-binding proteins in bovine mammary secretions associated with pregnancy and parturition.

The bovine mammary gland accumulates large quantities of insulin-like growth factors (IGFs) and IGF-binding proteins (IGFBPs) during late gestation which are secreted at parturition. The present study was conducted to determine the changes in the profiles of IGFBPs secreted by the mammary gland and in blood during late gestation and early lactation in dairy cows. Ligand blotting of serum and mammary secretions showed that IGFBPs of Mr 25,000, 30,000, 34,000, 42,000, 46,000 and greater than 200,000 were present in both fluids. The binding activity of the 42-46,000 Mr IGFBP predominated in prepartum mammary secretions and colostrum but was reduced postpartum. The binding activities of the 30,000 and 34,000 Mr IGFBPs, relative to other IGFBPs, were increased postpartum. Concentrations of IGF-I and IGF-II in mammary secretions declined from 347.1 and 181.1 nmol/litre 1 week prepartum to 0.7 and 0.3 nmol/litre 1.5 weeks postpartum. The volume of mammary secretions obtained was 0.109 litre and 6.690 litres at 1 week prepartum and 1.5 weeks postpartum respectively. In prepartum serum, the greatest binding activity was at Mr 42-46,000. The activity at this Mr decreased at parturition but was restored postpartum. The binding activities of the 30,000 and 34,000 Mr IGFBPs were increased around parturition. The 25,000 Mr IGFBP had minor activity during all periods. IGF-I concentrations decreased from 10.6 nmol/litres 1 week prepartum to 4.7 nmol/litres 1.5 weeks postpartum but IGF-II concentrations remained constant. In conclusion, IGFBP activity secreted by the mammary gland shifts from primarily Mr 42-46,000 prepartum to Mr 30,000 postpartum.(ABSTRACT TRUNCATED AT 250 WORDS)