Changes in Plasma Insulin-like Growth Factor (IGF)-1, IGF Binding Protein (IGFBP)-2 and IGFBP-3 during Fasting in Holstein Adult Steers and Calves

This study was conducted to investigate the effect of fasting on plasma insulin-like growth factor (IGF)-1, IGF binding protein (IGFBP)-2 and IGFBP-3 in two different growth stages of Holstein steers. Eight 4 month-old Holstein steer calves were treated with normal feeding and fasting for 3 days and four 18 month-old Holstein adult steers were treated 6 days. Plasma IGFBP-2 and IGFBP-3 were determined by western immunoblotting using the rabbit anti-bovine IGFBP-2 and-3 following SDS-PAGE electrophoresis. The immnunoblotting analysis demonstrated that the plasma IGFBP-3 band appeared at 38-43 kDa and plasma IGFBP-2 was localized at 34 kDa in plasma of adult and calves. Plasma IGF-1 and IGFBP-3 levels were higher in adult steers than calves (P<0.01) but plasma IGFBP-2 was lower in adult steers than in calves (P<0.01). Plasma IGF-1 and insulin levels were depressed during the fasting in adult steers and calves (P<0.05). On the other hand, plasma GH increased with fasting in both growth stages (P<0.05). Fasting from day two increased plasma IGFBP-2 and decreased IGFBP-3 in calves (P<0.05). In fasted adult steers, plasma IGFBP-2 increased from day three, whereas plasma IGFBP-3 decreased from day five (P<0.05). In conclusion, the contrasting response of plasma IGFBP-2 (positive) and IGFBP-3 (negative) to feed deprivation is similar in both adult and calves. The plasma IGFBP-2 was more sensitive to fasting than plasma IGFBP-3 in adult steers but not in calves. Thus, these results suggest that the different responses of IGFBP-2 and IGFBP-3 to nutritional status in blood may play an important role in the circulation of IGF-1 in all growth stages of steers, and that sensitivity to nutritional status between plasma IGFBP2 and IGFBP-3 is different according to age.