Growth hormone, IGF-I and insulin in mammary gland secretion before and after parturition and possibility of their transfer into the calf.

The aim of this study was to monitor the changes of growth hormone (GH), insulin-like growth factor I (IGF-I) and insulin in the secretion of the bovine mammary gland from day 70 ante partum (AP) till 6 days post partum (PP) and during entire lactation period. For comparable reasons additional blood concentrations were evaluated. The association of IGF-I with its binding proteins in milk was analysed. In a further experiment the possible transfer of IGF-I and insulin into the peripheral circulation of calves was evaluated after application of an enriched and from content defined colostrum pool. The hormones were determined by RIA. Highest level of IGF-I and insulin in milk were found 2 weeks AP followed by a rapid decrease during the first milkings PP. Blood concentrations were much lower and decreased at that time. Striking differences were found in the distribution of bound and free IGF-I AP compared with the first milkings (colostrum) PP. Most of the IGF-I was in a free form (not associated with binding proteins) in colostrum which contrasted to the secretion AP or 4 days after parturition or during entire lactation. Application of a colostrum pool (4.62 mg/2 1 vs milk 0.042 mg/2 l) to calves 6 h after parturition did not increase peripheral blood levels of IGF-I in contrast to insulin. Local effects of the peptide hormones in colostrum to the mammary gland and intestinal tract of the calf are assumed.(ABSTRACT TRUNCATED AT 250 WORDS)