Characterization of Endocrine Events During the Periestrous Period in Sheep After Estrous Synchronization with Controlled Internal Drug Release (CIDR) Device

Abstract

The Controlled Internal Drug Releasing (CIDR) device is an intravaginal pessary containing progesterone (P 4) designed for synchronizing estrus in ruminants. To date, there has been little information available on the timing, duration, and quality of the follicular phase after CIDR removal and how those characteristics compare with natural periovulatory endocrine events. The present communication relates the results of methods we used to characterize the endocrine events that followed CIDR synchronization. Breeding-season ewes were given an injection (10 mg) of Lutalyse (PGF 2α), and then studied during three consecutive estrous cycles, beginning in the luteal phase after the estrus induced by PGF 2α. Cycle 1 estrus was synchronized with 1 CIDR (Type G) inserted for 8 d beginning 10 d after PGF 2α. Cycles 2 and 3 were synchronized with two CIDRs for 8 d beginning 10 d after previous CIDR removal. Cycle 1 estrous behavior and serum gonadotropins showed a follicular phase (the interval from CIDR withdrawal to gonadotropin surge [surge] peak) of 38.2 ± 1.5 hr. Two CIDRs lengthened the interval to 46.2 ± 1.5 hr (P < 0.0001). At CIDR removal, circulating P 4 concentrations were higher in ewes treated with two CIDRs (5.1 ± 0.3 and 6.4 ± 0.4 ng/mL in Cycles 2 and 3 vs. 2.7 ± 0.3 ng/mL in Cycle 1), whereas estradiol concentrations were higher in the 1 CIDR cycle (3.3 ± 0.5 pg/mL in Cycle 1 vs. 0.5 ± 0.1, and 0.7 ± 0.2 pg/mL in Cycles 2 and 3), suggesting that the lower levels of P 4 achieved with one CIDR was not sufficient to arrest follicular development. There were no differences in any other endocrine variable. Both one and two CIDR synchronization concentrated surges within a 24-hr period in 92% of the ewes in Cycles 1 and 2. Cycle 3 ewes were euthanized at estimated luteal, early follicular, late follicular, LH surge, and secondary FSH rise timepoints. Endocrine data and ovaries showed that 88% of the ewes synchronized with two CIDRs were in the predicted stage of the estrous cycle. These data demonstrate that the CIDR device applied during the luteal phase effectively synchronizes estrus and results in a CIDR removal-to-surge interval of similar length to a natural follicular phase.