Equine chorionic gonadotropin and gonadotropin-releasing hormone enhance fertility in a norgestomet-based, timed artificial insemination protocol in suckled Nelore (Bos indicus) cows

Abstract

Two experiments were conducted to investigate the effects of equine chorionic gonadotropin (eCG) at progestin removal and gonadotropin-releasing hormone (GnRH) at timed artificial insemination (TAI) on ovarian follicular dynamics (Experiment 1) and pregnancy rates (Experiment 2) in suckled Nelore (Bos indicus) cows. Both experiments were 2x2 factorials (eCG or No eCG, and GnRH or No GnRH), with identical treatments. In Experiment 1, 50 anestrous cows, 134.5+/-2.3 d postpartum, received a 3mg norgestomet ear implant sc, plus 3mg norgestomet and 5mg estradiol valerate im on Day 0. The implant was removed on Day 9, with TAI 54 h later. Cows received 400 IU eCG or no further treatment on Day 9 and GnRH (100 microg gonadorelin) or no further treatment at TAI. Treatment with eCG increased the growth rate of the largest follicle from Days 9 to 11 (means+/-SEM, 1.53+/-0.1 vs. 0.48+/-0.1mm/d; P<0.0001), its diameter on Day 11 (11.4+/-0.6 vs. 9.3+/-0.7 mm; P=0.03), as well as ovulation rate (80.8% vs. 50.0%, P=0.02), whereas GnRH improved the synchrony of ovulation (72.0+/-1.1 vs. 71.1+/-2.0 h). In Experiment 2 (n=599 cows, 40 to 120 d postpartum), pregnancy rates differed (P=0.004) among groups (27.6%, 40.1%, 47.7%, and 55.7% for Control, GnRH, eCG, and eCG+GnRH groups). Both eCG and GnRH improved pregnancy rates (51.7% vs. 33.8%, P=0.002; and 48.0% vs 37.6%, P=0.02, respectively), although their effects were not additive (no significant interaction). In conclusion, eCG at norgestomet implant removal increased the growth rate of the largest follicle (LF) from implant removal to TAI, the diameter of the LF at TAI, and rates of ovulation and pregnancy rates. Furthermore, GnRH at TAI improved the synchrony of ovulations and pregnancy rates in postpartum Nelore cows treated with a norgestomet-based TAI protocol.

Follicle and corpus luteum size and vascularity as predictors of fertility at the time of artificial insemination and embryo transfer in beef cattle

“…Follicle and CL size were also positive related (Wecker et al 2012), but no interference in fertility was noted. In the present study, no relationship between CL size with fertility was noted, similarly as observed by Nuñes et al (2011), although disagreeing with findings from Baruselli et al (2003), Baruselli et al (2004) and Sá Filho et al (2010a, 2010b, 2010c.…”

Preovulatory follicle diameter, growth rate and time of ovulation during induced oestrus using a CIDR® in trypanotolerant female Bos taurus N’Dama cattle

“…Animals injected with eCG (300 IU) present a greater ovulating follicle diameter (10.1±1.4 mm) than the control group (9.3±1.2 mm). Similar differences were observed after injection of 400 IU of eCG in Nelore cows (Bos indicus) (11.2 ±0.9 mm vs. 9.4±1.1 mm) (Sà Filho et al 2010a) This is lower than the diameters observed by several authors after injecting 400 IU of eCG in Nelore cattle: 10.6±0.2 mm, 11.2±0.9 and 12.55±0.36 mm (Baruselli et al 2004;Sà Filho et al 2010a, c), or Senepol cattle: 13.6±0.4 mm (Alvarez et al 2000). These differences could be attributed to speculation and therefore the different physiological statuses of the B. taurus breeds.…”

“…Injection of 400 IU of eCG in 90 Nelore heifers presented a preovulatory follicle growth rate of 1.1±0.1 mm/day, while this was 0.6 ±0.1 mm/day in the 87 animals in the control group (Sà Filho et al 2010b). The same is true of Nelore cows treated with 400 IU of eCG: follicle growth rate was 1.5±0.1 mm/day compared to 0.56±0.2 mm/day in untreated cows (Sà Filho et al 2010a). Animals injected with eCG (300 IU) present a greater ovulating follicle diameter (10.1±1.4 mm) than the control group (9.3±1.2 mm).…”

“…Injections of eCG had no effect on this interval. Intervals of 72.9±2.1 h and 70.5± 2.7 h were observed after dairy cattle were treated with a CIDR® and 400 IU of eCG (Souza et al 2009) and Nelore cattle treated using a norgestomet implant and 400 IU of eCG (Sà Filho et al 2010a). Injection of 400 IU of eCG did not lead to significant differences in this interval in Nelore cows treated using progesterone, 74.2±4.0 h in treated cattle compared to 78.0±3.1 h in cows in the control group (Baruselli et al 2004).…”

“…Ovulation takes place 26.7±5.4 h after the start of heat in dairy breeds (Walker et al 1996). The interval between stopping progesterone-based treatment and ovulation varies between 69.6±2.4 h to 73.1±1 h in the Zebu Nelore (Sà Filho et al 2010a) and from 65.4±2.2 to 66.0±3.3 h in other dairy breeds (Uslenghi et al 2014). Few data are available in the literature on this interval in N'Dama cattle.…”