Serum concentrations of progesterone in cows treated with injectable progesterone

The aim of the study was to evaluate the profile of circulating progesterone (P4) induced by treatment with injectable P4 in cows. Two products were used: Afisterone® (1 g/100 mL, Hertape Calier, Brazil) and Progestar® (2.5 g/100 mL, Syntex, Argentina). Non-lactating and non-pregnant Holstein cows (n = 20) were remained for 7 d with an intravaginal P4 device (Sincrogest®, Ourofino, Brazil). After withdrawal (D-8), a norgestomet ear implant (Crestar®, MSD, Brazil) was inserted and maintained for 8 d. At D-8 and D-7, 0.526 mg of PGF2α (Sincrocio®, Ourofino, Brazil) was applied. At D0, cows were randomized to receive Afisterone (50 mg, n = 10) or Progestar (50 mg, n = 10). From the time of P4 injection, blood samples were taken at 0, 2, 6, 12, 24, 48, 72, 96, 120, 144, 168 and 192 h to verify the profile of serum P4 by enzyme immunoassay (ELISA, Enzyme-Linked immunosorbent Assay, adapted Rasmussen et al., J. Dairy Sci, v.79, p.227-234, 1996). Statistical analysis was performed using Proc-Mixed of SAS (9.2; repeated measures), accepting significance at P < 0.05. Data are shown as least squares means ± SEM. There was no effect of treatment, but there was effect of time. At 2 h, Progestar treatment reached the highest concentration of P4 (1.21 ± 0.18 ng/mL), while for Afisterone, the peak occurred at 6 h (0.95 ± 0.16 ng/mL). The average circulating P4 concentration over all periods after treatments were 0.41 ± 0.04 and 0.44 ± 0.04 ng/mL for Afisterone and Progestar, respectively. At other periods, circulating P4, regardless of treatment, was: 12 h (0.70 ± 0.13 ng/mL), 24 h (0.43 ± 0.08 ng/mL), 48 h (0,30 ± 0.09 ng/mL), 72 h (0.20 ± 0.05 ng/mL), 96 h (0.20 ± 0.03 ng/mL), 120 h (0.20 ± 0.04 ng/mL), 144 h (0.18 ± 0.03 ng/mL), 168 h (0.19 ± 0.04 ng/mL) and 192 h (0.20 ± 0.08 ng/mL). Due to the low serum concentrations of P4 obtained by using 50 mg of injectable P4, independent of the commercial product used, it is suggested that this dose routinely recommended in protocols for synchronization of wave emergence is insufficient to aid regression (turnover) of follicles at the beginning of the protocols, in combination with estradiol esters.