Use of Estradiol Cypionate as a Substitute for GnRH in Protocols for Synchronizing Ovulation in Dairy Cattle

Abstract

Our purpose was to determine whether estradiol cypionate (ECP) could be substituted for the second GnRH injection of the standard Ovsynch protocol (injection of GnRH given 7 d before and 48 h after PGF(2alpha), with timed AI [TAI] 12 to 20 h after the second GnRH injection). Lactating dairy cows ranging from 61 to 82 d in milk at TAI were studied in 14 replicates. Main effects were hormone (ECP vs. GnRH) to induce ovulation and exposure to progesterone (P4) or not during the week preceding PGF(2alpha)-induced luteolysis. Four treatments were: 1) 100 microg of GnRH at 48 h after PGF(2alpha) (Ovsynch; n = 27); 2) same as Ovsynch, plus a P4-releasing intravaginal insert (CIDR) placed for 7 d beginning at the first GnRH injection (Ovsynch + CIDR, n = 20); 3) same as Ovsynch, but substituting 1 mg of ECP for GnRH, and injecting ECP at 24 h after PGF(2alpha) (Heatsynch; n = 33); or 4) Heatsynch + CIDR (n = 26). The largest follicle was identified by ultrasonography 24 h after PGF(2alpha) and was monitored every 6 h until ovulation. Incidence of estrus was less after GnRH (54%) than after ECP (87%), but more GnRH-treated cows had LH surges detected (95 vs. 65%) and ovulated (100 vs. 86%). Duration of LH surges, but not peak concentrations, was less after GnRH than after ECP (6.1 +/- 0.7 vs. 12.2 +/- 0.9 h). Pre-treatment with P4 reduced the incidence of LH surges but had no effects on incidence of estrus or ovulation. Intervals to the LH surge and ovulation were less after GnRH than after ECP, but intervals between onset of the LH surge and ovulation did not differ (26 +/- 2 vs. 30 +/- 3 h). We concluded that substituting ECP for GnRH resulted in more cows in estrus and slightly fewer ovulating.

Effects of preovulatory estradiol on embryo survival and pregnancy establishment in beef cows

“…Cows treated with ECP had two surges of LH the first 25 h after treatment with ECP and the second after treatment with GnRH. This is a shorter interval than the 42 h interval from ECP treatment to the LH surge reported by Stevenson et al (2004); however, a greater dose of ECP was utilized in the present study. Cows in both the EB and CON treatments had a LH surge following treatment with GnRH.…”

Development of Ovulation Synchronization and Fixed Time Artificial Insemination in Dairy Cows

“…More recently, Presynch-Ovsynch protocol, which administers PGF 2α twice at a 14 d interval before Ovsynch/TAI, was developed [65]. Occurrence of estrus and ovulation before TAI during Ovsynch protocol can also be eliminated by using CIDR inserted from the day of Ovsynch to the PGF 2α administration (CIDR-Ovsynch) [66]. Heatsynch is basically similar to Ovsynch [67].…”

Inducing ovulation with oestradiol cypionate allows flexibility in the timing of insemination and removes the need for gonadotrophin-releasing hormone in timed AI protocols for dairy cows

“…In terms of animal handling, the use of EC at device removal or GnRH at TAI as ovulatory stimuli requires is the same. However, several studies have reported on the use of GnRH 10-24 h before TAI (Pancarci et al 2002;Stevenson et al 2004;Sellars et al 2006;Souza et al 2008Souza et al , 2009Herlihy et al 2012;Ayres et al 2013). In these cases, the replacement of GnRH with EC at device removal can bring about the advantage of reducing animal handling by one time (Souza et al 2009).…”