Neither plasma progesterone concentrations nor exogenous eCG affects rates of ovulation or pregnancy in fixed-time artificial insemination (FTAI) protocols for puberal Nellore heifers

• Published in: Theriogenology 2011, Vol.75 (1), p.17-23
• Main Authors: Pegorer, M. Figueira, Ereno, R.L., Satrapa, R.A., Pinheiro, V.G., Trinca, L.A., Barros, C.M.
• Format: Article
• Language: English
• Subjects: Animals; artificial insemination; biomarkers; blood plasma; Bos indicus; Cattle - physiology; Chorionic Gonadotropin - pharmacology; cloprostenol; controlled internal drug release devices; cows; equine chorionic gonadotropin; estradiol; Estradiol - analogs & derivatives; Estradiol - pharmacology; estrus synchronization; Female; female fertility; Fixed-time artificial insemination; follicular development; heifers; hormonal regulation; Insemination, Artificial - methods; Insemination, Artificial - veterinary; methodology; Nellore; Nellore heifers; ovulation; Ovulation - drug effects; Ovulation - physiology; Ovulation Induction; Pregnancy; Pregnancy Rate; Progesterone; Progesterone - blood; Progesterone - pharmacology; Prostaglandins F - pharmacology
• ISSN: 0093-691X; 1879-3231
• DOI: 10.1016/j.theriogenology.2010.07.005

The objective was to evaluate the effects of plasma progesterone (P4) concentrations and exogenous eCG on ovulation and pregnancy rates of pubertal Nellore heifers in fixed-time artificial insemination (FTAI) protocols. In Experiment 1 (Exp. 1), on Day 0 (7 d after ovulation), heifers (n = 15) were given 2 mg of estradiol benzoate (EB) im and randomly allocated to receive: an intravaginal progesterone-releasing device containing 0.558 g of P4 (group 0.5G, n = 4); an intravaginal device containing 1 g of P4 (group 1G, n = 4); 0.558 g of P4 and PGF 2α (PGF; 150 μg d-cloprostenol, group 0.5G/PGF, n = 4); or 1 g of P4 and PGF (group 1G/PGF, n = 3). On Day 8, PGF was given to all heifers and intravaginal devices removed; 24 h later (Day 9), all heifers were given 1 mg EB im. In Exp. 2, pubertal Nellore heifers (n = 292) were treated as in Exp. 1, with FTAI on Day 10 (30 to 36 h after EB). In Exp. 3, pubertal heifers (n = 459) received the treatments described for groups 0.5G/PGF and 1G/PGF and were also given 300 IU of eCG im (groups 0.5G/PGF/eCG and 1G/PGF/eCG) at device removal (Day 8). In Exp. 1, plasma P4 concentrations were significantly higher in heifers that received 1.0 vs 0.588 g P4, and were significantly lower in heifers that received PGF on Day 0. In Exp. 2 and 3, there were no significant differences among groups in rates of ovulation (65–77%) or pregnancy (Exp. 2: 26–33%; Exp. 3: 39–43%). In Exp. 3, diameter of the dominant ovarian follicle on Day 9 was larger in heifers given 0.558 g vs 1.0 g P4 (10.3 ± 0.2 vs 9.3 ± 0.2 mm; P < 0.01). In conclusion, lesser amounts of P4 in the intravaginal device or PGF on Day 0 decreased plasma P4 from Days 1 to 8 and increased diameter of the dominant follicle on Day 9. However, neither of these nor 300 IU of eCG on Day 8 significantly increased rates of ovulation or pregnancy.