The effects of gonadotrophin releasing hormone in prostaglandin F_2α-based timed insemination programs for beef cattle

Abstract

R. 2001. The effects of gonadotrophin releasing hormone in prostaglandin F 2α α -based timed insemination programs for beef cattle. Can. J. Anim. Sci. 81: 335-343. Trials were conducted in the spring (May; n = 324) and fall (October; n = 132) with crossbred continental-type beef cows assigned on the basis of parity and postpartum interval to one of three timed-AI treatments and one of two post-AI treatments. The timed-AI treatments were: (DPG) double (14 d apart) PGF 2α (Lutalyse ® ) and AI (day = 0) 72 h after the second PGF 2α (day -3); (OVS) Ovsynch ® with the second GnRH (Factrel ® ) at 48 h and AI at 66 h; and (BRC) the same as OVS except that the second GnRH was given at the time of AI. Half of the cows within each treatment were given GnRH on day 14. Plasma progesterone concentrations were determined for the day of the first injection and on days -3, 0, 14, and 21. Timed-AI pregnancy was diagnosed by ultrasonography at day 42 and confirmed at calving. For DPG, OVS and BRC, PGF 2α responder rates were 75.9, 51.4 and 71.3%, respectively, in spring (P < 0.05) and 70.4, 70.4 and 59.1% in fall (P > 0.05), and AI pregnancy rates were 28.7, 44.9 and 44.4% in spring (P < 0.05) and 25.0, 40.9 and 43.2% in fall (P > 0.05). Post-AI GnRH had no significant effect on pregnancy or conception rates or day 21 progesterone. The use of GnRH in the PGF 2α based timed-AI program improved pregnancy rates and the BRC treatment was as effective as OVS. Neither postpartum interval nor initial progesterone concentration influenced (P > 0.05) the effect of GnRH on AI pregnancy rate, and GnRH had no effect (P > 0.05) on twinning rate or gender ratio.

Effects of postpartum energy intake on pregnancy rates in beef cattle subjected to GnRH- or CIDR-based timed artificial insemination protocols

“…In agreement with other studies using similar protocols in suckled beef cows (Geary et al 1998;Martinez et al 2000;Small et al 2001) both the OVS and CIDR protocols resulted in a high degree of ovulation synchrony, with acceptable TAI pregnancy rates. This appeared to hold true over a range of postpartum ME intakes.…”

“…To attain acceptable TAI pregnancy rates, ovulation must be highly synchronous and should occur on or around the day of insemination (Small et al 2001). To achieve this, truncation of the randomly staged follicular waves, and the induction of new, synchronous follicular waves must occur approximately 1 wk before the synchronous ovulation is required, so dominant follicles in all cows reach maturity at approximately the same time.…”

Effects of presynchronization and eCG on pregnancy rates to GnRH-based, fixed-time artificial insemination in beef heifers

“…The TAI pregnancy rates in these studies seemed generally comparable to those reported previously (Pursley et al 1997;Small et al 2001;Johnson and day 2004;Lamb et al 2006), except for the somewhat lower pregnancy rates in Herd A in exp. 3.…”

“…Mots clé s: Pre´-synchronisation, gonadotrophine chorionique e´quine, GnRH, inse´mination artificielle a`pe´riode fixe, progeste´rone Current gonadotropin releasing hormone (GnRH)-based synchronization protocols for fixed-time AI (TAI) of cattle (Pursley et al 1995;Small et al 2001) typically consist of two GnRH treatments 9 d apart, with prostaglandin F 2a (PGF) 7 d after the first GnRH, and TAI either 16 to 18 h after the second GnRH (Ovsynch), or concurrent with the second GnRH (COSynch). Pregnancy rates have been lower in heifers than cows subjected to these protocols (Pursley et al 1997;, but were generally improved in heifers by inseminating those observed in estrus prior to scheduled TAI (Johnson and Day 2004).…”

In vitro assessment of corpus luteum function in cattle following Ovsynch and CIDR ovulation synchronization protocols

“…Both are PGF 2α -based protocols modified to synchronize the development of the ovulatory follicle as well as ovulation. The Ovsynch procedure uses an initial injection of GnRH to synchronize follicular wave emergence and a second GnRH to synchronize ovulation (Pursley et al 1995;Hirad et al 1999;Small et al 2001). The CIDR protocol uses an initial injection of progesterone and estradiol-17β and an intravaginal progesterone-releasing device to synchronize follicular wave emergence and a second estradiol-17β to synchronize ovulation (Martinez et al 2000).…”