Role of progesterone concentrations during early follicular development in beef cattle: I. Characteristics of LH secretion and oocyte quality

• Published in: Animal reproduction science Vol. 196; pp. 59 - 68
• Main Authors: Abreu, F.M., Coutinho da Silva, M.A., Cruppe, L.H., Mussard, M.L., Bridges, G.A., Harstine, B.R., Smith, G.W., Geary, T.W., Day, M.L.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01-09-2018
• Subjects: Animals; Cattle; Corpus Luteum - cytology; Corpus Luteum - drug effects; Corpus Luteum - physiology; Estrus Synchronization; Female; Luteinizing hormone; Luteinizing Hormone - drug effects; Luteinizing Hormone - secretion; Oocyte competence; Oocytes - cytology; Oocytes - drug effects; Oocytes - physiology; Ovarian Follicle - cytology; Ovarian Follicle - drug effects; Ovarian Follicle - physiology; Ovulation; Progesterone; Progesterone - pharmacology; Progestins - pharmacology; Used CIDR; Luteinizing hormone; Progesterone; Used CIDR; Oocyte competence
• ISSN: 0378-4320; 1873-2232
• DOI: 10.1016/j.anireprosci.2018.06.020

Objective was to investigate the effect of different progesterone (P4) concentrations during early follicular development on luteinizing hormone (LH) secretion and oocyte characteristics in beef cows. Primiparous cows (n = 24) were estrous pre-synchronized and follicular ablation was performed (d 0) 6 days following the time of ovulation. At the time of follicular ablation, cows were assigned to either: 1) high P4 treatment - HiP4; a new CIDR was inserted on d 0 to supplement P4 from the existing corpus luteum [CL], or 2) low P4 treatment - LoP4; a previously-used CIDR and two doses of PGF 8 to 12 h apart were given on d 0. Concentrations of P4 were greater (P < 0.01) in the cows of the HiP4 than LoP4 group on d 1.5, 2.5, and 3.5. Peripheral concentrations of E2 were greater (P < 0.05) in the cows of the LoP4 than HiP4 group on d 2.5 and 3.5. Frequency of LH pulses was greater (P <  0.05) in the LoP4 than HiP4 group on d 2.5, but mean LH concentration and pulse amplitude did not differ between treatments. Number of follicles aspirated per cow, total oocytes recovered, recovery rate, percentage of oocytes graded 1 to 3, oocyte diameter, percentage BCB+ oocytes, and relative abundance of oocyte mRNA for FST did not differ (P >  0.10) between treatments. In conclusion, lower P4 concentrations during early follicular development resulted in increased LH pulse frequency and E2 concentrations, but did not affect characteristics of oocyte developmental competence.