55 Parturition in cattle: predictors and hormonal profile

This study aimed to understand the physiological mechanisms regulating parturition and to identify potential biomarkers to predict the onset of birth. Additionally, we compared hormone profiles between cows with shorter and longer gestation lengths. Twenty-eight days before due date, primiparous and multiparous Holstein cows (n = 18; lactation = 2.3; and body condition score: 3.14) were blood samples daily from 28 days before due date until 3 days postpartum. Circulating progesterone (P4), oestradiol (E2), testosterone (TST), prostaglandin F_2a metabolite (PGFM), and pregnancy-specific protein B (PSPB) concentrations were evaluated daily and normalized to day of gestation and day of parturition to compare cows with shorter (n = 6; 276–278 days) and longer (n = 9; 282–285 days) gestation lengths. Cortisol (CTS) and lactate were only normalized to the day of parturition to compare the gestation length. Progesterone and E2 were evaluated by radioimmunoassay, TST, CTS, PGFM, and PSPB by ELISA, and lactate by colourimetric assay. Data were analysed by GLIMMIX procedure of SAS. At the end of gestation, P4 decreases (P < 0.01) gradually from Day −14 to −4 (from 3.6 ± 0.4 to 1.4 ± 0.2 ng/mL, respectively) with a rapid decrease to undetectable concentrations from Day −2 to parturition (from 1.3 ± 0.2 to 0.1 ± 0.01 ng/mL, respectively). In contrast, PGFM increased (P < 0.01) only from Day 2 to parturition (from 249.7 ± 41.1 to 2868.4 pg/mL, respectively). E2 increased (P < 0.01) gradually from Day 13 to parturition ~9-fold (from 27.8 ± 5.3 on Day −14 to 258.5 ± 50.2 pg/mL, respectively). The PSPB first increased on d-12, followed by an increase of ~8-fold by d-3 (from 4.3 ± 0.1 to 583.9 ± 78.9 ng/mL), and then a gradual decrease occurred by d3 (268.5 ± 36.7 ng/mL). TST decreased (P < 0.01) from Day −5 to 3 (from 109.8 ± 15.2 to 12.9 ± 1.8 pg/mL, respectively). Cortisol (2.7 ± 0.5 to 6.1 ± 0.6 to 3.4 ± 0.5 ng/mL for Day −10, 0, and 1, respectively) and lactate (8.7 ± 0.7 to 19.4 ± 1.6 to 10.9 ± 0.9, mmol/L for Day −10, 0, and 1, respectively) increased (P < 0.01) only at calving and decreased the subsequent day. Normalized to the day of gestation, cows with shorter gestation lengths had a lower circulating P4 concentration and greater circulating E2, PGFM, and PSPB concentrations at same times in gestation period compared to cows with longer gestation. Normalized to parturition, a slight difference was detected in the circulating E2 and PGFM patterns between shorter and longer gestation cows. When data were normalized to parturition, no difference was observed in circulating P4 and PSPB. In both normalizations, TST did not differ by gestation length. Thus, the first significant hormonal changes associated with parturition begin at 14 days before parturition. Moreover, two clear biomarkers of impending parturition are E2 and PSPB, and these could also be used as markers of final placental maturation before parturition. Cows with shorter and longer gestation had substantial differences in hormones when data were normalized to gestation day; however, only slight differences (E2 and PGFM) when normalized to day of parturition.

This work was funded by USDA NIFA Grant 2020–67015–31260 and Dairy Innovation Hub.