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IN VITRO ASSESSMENT OF THE CORPUS LUTEUM FUNCTION IN CATTLE FOLLOWING "OVSYNCH" AND CIDR ESTRUS SYNCHRONIZATION PROTOCOLS.
Aali, Muhammad1, Small, Julie2, Cheng, Kimberly1, Rajamahendran, Rajadirai1, 1 2
ABSTRACT- The objective of this experiment was to compare in vitro progesterone (P4) production in corpora lutea (CL) collected at different stages of the estrous cycle, early (E), middle (M), and late (L), following synchronization of estrus and ovulation with the controlled intravaginal drug release device (CIDR) and "Ovsynch" synchronization protocols. Thirty-three beef cows were randomly divided into the "Ovsynch" group (n = 17) and the CIDR group (n = 16). The "Ovsynch" protocol consisted of a gonadotropin-releasing hormone (GnRH) injection (100 
g), followed by prostaglandin- F2
(PGF2) injection (25 g) 7 d later and a second GnRH injection (100 g) 48 h after PGF2; the CIDR protocol consisted of insertion of CIDR and injection of P4 (100 mg) and estradiol (E2; 5 mg) on Day 0, a PGF2 injection (25 mg) 7 d later, and a second E2 injection on d 9 after removal of CIDR on d 8. Following synchronization, CL enucleation was carried out on days 6-8 (E), 13-15 (M), and 19-21 (L) of the synchronized cycle. CL tissue (50 mg) cultured (pre-incubation, without treatments, 1 h; with treatments, 6 h) in serum-contained DMEM/HAM-F-12 media with four different hormone treatments; LH (500 ng/ml), PGF2 (500 ng/ml), LH + PGF2 (500 ng/ml + 500 ng/ml), and without hormone treatment (control). At the end of the culture period (1 h and 6 h), media was collected and analyzed by by RIA for P4. In relation to treatments effects, the P4 production was similar (p > 0.05) between "Ovsynch" and CIDR at all stages of the cycle. A stage X hormone interaction (p < 0.05) indicated that in the early and middle stages of the cycle, P4 production was highest in LH + PGF2 treatment in both protocols, followed by LH and PGF2 which were not different (p > 0.05) from the control. Conclusion: The CL formed after the CIDR and "Ovsynch" synchronization protocols yielded similar in vitro P4 concentrations at different stages of the synchronized cycle.
KEY WORDS: CATTLE, PROGESTERONE, CIDR, OVSYNCH