Association between IGF-1 and IGFBPs in Blood and Follicular Fluid in Dairy Cows Under Field Conditions

Insulin-like growth factor 1 (IGF-1) regulates dairy cow reproduction, while the paracrine IGF system locally influences fertility. In both systems, IGF-1 bioactivity is regulated through binding proteins (IGFBPs) inhibiting IGF-1 binding to its receptor (IGF1R). This study aimed to investigate a possible transfer between this endocrine and paracrine system. Therefore, blood and follicular fluid (FF) from postpartum dairy cows were analysed for ß-hydroxybutyrate (BHB), IGF-1, IGFBP-2, -3, -4, -5, and an IGFBP fragment in two study parts. The mRNA expression of IGFBP-2, IGFBP-4, IGF1R, and the pregnancy-associated plasma protein A (PAPP-A) in granulosa cells was measured. The results showed correlations between plasma and FF for IGF-1 (r = 0.57, p < 0.001) and IGFBP-2 (r = -0.57, p < 0.05). Blood BHB negatively correlated with IGF-1 in blood and FF and IGFBP-3, -5 and total IGFBP in blood (IGF-1 plasma: r = -0.26, p < 0.05; FF: r = -0.35, p < 0.05; IGFBP-3: r = -0.64, p = 0.006; IGFBP-5: r = -0.49, p < 0.05; total IGFBP: r = -0.52, p < 0.05). A negative correlation was found between IGFBP-2 expression and IGF-1 concentration in FF (r = -0.97, p = 0.001), while an IGFBP fragment positively correlated with IGF1R-mRNA in FF (r = 0.82, p = 0.042). These findings suggest a transfer and local regulation between the somatotropic axis and the follicular IGF system, linking the metabolic status with local effects on dairy cow fertility.