Ovarian function in Nelore ( Bos taurus indicus) cows after post-ovulation hormonal treatments

• Published in: Theriogenology 2008-04, Vol.69 (7), p.798-804
• Main Authors: Machado, R., Bergamaschi, M.A.C.M., Barbosa, R.T., de Oliveira, C.A., Binelli, M.
• Format: Article
• Language: English
• Subjects: accessory corpus luteum; Animals; Antiluteolytic strategies; beef cows; Buserelin - therapeutic use; Cattle; Cattle - physiology; Chorionic Gonadotropin - administration & dosage; Cloprostenol - administration & dosage; corpus luteum; Drug Administration Schedule; Estradiol; Estradiol - administration & dosage; Estrous Cycle - drug effects; estrus; Estrus Synchronization - methods; Female; follicular development; gonadotropin-releasing hormone; Gonadotropins; hormonal regulation; hormone secretion; human chorionic gonadotropin; luteal function; luteolysis; Luteolytic Agents - administration & dosage; Male; Nellore; Organ Size - drug effects; ovarian follicles; Ovary; Ovary - anatomy & histology; Ovary - drug effects; Ovary - physiology; ovulation; Ovulation - drug effects; Ovulation Induction - methods; Ovulation Induction - veterinary; progesterone; prostaglandins
• ISSN: 0093-691X; 1879-3231
• DOI: 10.1016/j.theriogenology.2007.10.025

Maternal recognition of pregnancy in the cow requires successful signaling by the conceptus to block luteolysis. Conceptus growth and function depend on an optimal uterine environment, regulated by luteal progesterone. The objective of this study was to test strategies to optimize luteal function, as well as prevent a dominant follicle from initiating luteolysis. Nelore ( Bos taurus indicus) beef cows ( n = 40) were submitted to a GnRH/PGF 2α/GnRH protocol. Cows that ovulated from a dominant ovarian follicle (ovulation = Day 0) were allocated to receive: no additional treatment (G C; n = 7); 3000 IU of hCG on Day 5 (G hCG; n = 5); 5 mg of estradiol-17β on Day 12 (G E2; n = 6); or 3000 IU of hCG on Day 5 and 5 mg of estradiol-17β on Day 12 (G hCG/E2; n = 5). Ultrasonographic imaging of the ovaries, assessment of plasma progesterone concentration, and detection of estrus were done daily from Day 5 to the day of subsequent ovulation. Treatment with hCG induced an accessory CL, increased CL volume, and plasma progesterone concentration throughout the luteal phase ( P < 0.01). Estradiol-17β induced atresia and recruitment of a new wave of follicular growth; it eliminated a potentially estrogen-active, growing ovarian follicle within the critical period for maternal recognition of pregnancy, but it also hastened luteolysis (Days 16 or 17 vs. Days 18 or 19 in non-treated cows). In conclusion, the approaches tested enhanced luteal function (hCG) and altered ovarian follicular dynamics (estradiol-17β), but were unable to extend the life-span of the CL in Nelore cows.