Insulin-like growth factor-I (IGF-I) and thyroid hormone concentrations in colostrum of Holstein-Friesian cows before and after calving

The concentration of biologically active molecules in colostrum is strongly related to the metabolic and endocrine status of the cow during the early postpartum period. The aim of this study was to determine concentrations of insulin like growth factor-I (IGF-I), triiodothyronine (T3) and thyroxine (T4) in mammary gland secretion during the late dry and colostral period and its possible association with the energy status of the cows as represented by blood glucose concentration. Ten healthy Holstein-Friesian dairy cows were involved in this study. Two samples of colostrum were taken from each animal: one between 19 and 53 hours (mean [sd] 32.10 [9.47] hours) before calving, and the second 2 hours after calving. Concentrations of IGF-I, T3 and T4 tended to decrease at the start of lactation but the changes were not statistically significant. Linear regression of colostral IGF-I and protein concentration before calving revealed a positive relationship (R2 = 0.668, p<0.01) before calving but not post partum (R2 = 0.348, p>0.05). Blood glucose concentration was 2.88 ± 0.32 mmol/L before and 2.28 ± 0.29 mmol/L after calving and the decrease was statistically significant (p<0.001). Blood glucose levels after calving were positively correlated with colostral IGF-I concentration after calving (R2 = 0.695, p<0.01), but not before parturition (R2 = 0.383, p>0.05).