Efficiency of CIDR-Based Protocols Including GnRH Instead of eCG for Estrus Synchronization in Sheep.

Paula Martinez-Ros,Antonio Gonzalez-Bulnes

doi:10.3390/ani9040146

Abstract

Simple SummaryThis study examines the preovulatory and ovulatory events (in terms of the timing of onset of estrus behavior, preovulatory LH surge, and ovulation) and the yields obtained (in terms of ovulation rate, progesterone secretion, and fertility) after insertion of controlled internal drug release (CIDR) devices for 5 days and treatment with equine chorionic gonadotrophin (eCG) or gonadotrophin-releasing hormone (GnRH).The present study examined, for meat sheep (Segureña breed; 2–5-years old, mean body score of 3.5 ± 0.5), the timings of onset of estrus behavior, preovulatory luteinizing hormone (LH) surge and ovulation, and the ovulation rate and fertility obtained after insertion of controlled internal drug release (CIDR) devices for 5 days plus treatment with equine chorionic gonadotrophin (eCG; single dose at CIDR removal, n = 19 ewes) or gonadotrophin-releasing hormone (GnRH, either in a single dose at 56 h after CIDR removal, group CIDR-GnRH, n = 19 ewes; or in one dose at CIDR insertion and another dose 56 h after CIDR removal, group GnRH-CIDR-GnRH, n = 19 ewes). In all the ewes, the appearance of estrus behavior ranged between 84% and 90% and all females showing estrus signs had subsequent preovulatory LH peaks and ovulations. Onset of these events was earlier in the CIDR-eCG group than in the CIDR-GnRH and GnRH-CIDR-GnRH groups (p < 0.05). These differences were mainly determined by the onset of estrus behavior, since timing and intervals of LH peak and ovulation were similar among treatments. In fact, the range of ovulations was narrower in the GnRH-CIDR-GnRH group, which suggests better synchronization of follicular growth (p < 0.05). In conclusion, protocols with two doses of GnRH offer similar yields to eCG protocols.

Highlights

Reproductive management of sheep, like in other domestic species, is commonly based on the induction and synchronization of estrus and ovulation, either in reproductive or nonreproductive season and either for natural mating or artificial insemination, by the use of pharmacological treatments [1].Such treatments, from seminal studies in the 1950s [2], are mostly based on the administration of progesterone or its analogues for mimicking the activity of the corpus luteum
There were, on the other hand, significant differences in the timing of estrus onset, and the group treated with equine chorionic gonadotrophin (eCG) had a significantly earlier appearance of estrus signs than the groups treated with gonadotrophin-releasing hormone (GnRH) (p < 0.05)
The range of appearance of estrus behavior was similar for the controlled internal drug release (CIDR)-eCG and CIDR-GnRH groups

Summary

Introduction

Reproductive management of sheep, like in other domestic species, is commonly based on the induction and synchronization of estrus and ovulation, either in reproductive or nonreproductive season and either for natural mating or artificial insemination, by the use of pharmacological treatments [1] Such treatments, from seminal studies in the 1950s [2], are mostly based on the administration of progesterone or its analogues for mimicking the activity of the corpus luteum. Without eCG, preovulatory events and fertility after 5 days are better than after 6 or 7 days of CIDR insertion and similar to those obtained by the use of classical treatments with 14 days of CIDR insertion plus eCG at device removal These findings may indicate that the dominant follicle induced by CIDR insertion would be at the height of its growing phase 5 days later and, in case of CIDR withdrawal, would be able to ovulate without eCG stimulation. 1 or 2 days after, it would be in the static or regressing phase and, its ability to ovulate without eCG stimulation would be compromised

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