Hormonal profiles and biomarkers leading to parturition in cattle†.

This study aimed to understand the physiological mechanisms regulating parturition and to identify potential biomarkers to predict onset of birth. Additionally, we compared hormone profiles between cows with shorter and longer gestation lengths. Twenty-eight days before due date until 3d postpartum, cows (n = 18) were blood-sampled daily. Circulating concentrations were measured for progesterone and estradiol by RIA, testosterone, prostaglandin F2α metabolite, cortisol, pregnancy-specific protein B by enzyme-linked immunosorbent assay, and lactate concentrations by colorimetric assay. At end of gestation, progesterone decreased from d-14 to d-4 (from 3.6 to 1.4 ng/mL), most likely from rapid loss of placental progesterone production (64% of decline in 24 h). A second rapid decrease in progesterone to undetectable concentrations was observed from d-2 to parturition (from 1.4 to 0.1 ng/ml; most likely luteal origin) corresponding to increase in prostaglandin F2α metabolite from d-2 to parturition (249.7 to 2868.4 pg/mL). E2 and pregnancy-specific protein B increased ~8-fold from ~13d before parturition with acute rise in E2 but not pregnancy-specific protein B (45% vs. 13% in first 24 h). Testosterone decreased slightly during the same period. Cortisol and lactate increased only at calving. Comparison of cows with shorter vs. longer gestation, when data were normalized to parturition day, a difference was detected in circulating E2 and prostaglandin F2α metabolite patterns, but not progesterone and pregnancy-specific protein B. Thus, the first significant hormonal changes associated with parturition begin at d-14 with E2 and pregnancy-specific protein B as two clear biomarkers of impending parturition. Cows with shorter and longer gestation had hormonal differences indicative of identifiable earlier placental maturation.