Effects of equine chorionic gonadotropin and type of ovulatory stimulus in a timed-AI protocol on reproductive responses in dairy cows

Abstract

The objectives were to evaluate the effects of equine chorionic gonadotropin (eCG) supplementation (with or without eCG) and type of ovulatory stimulus (GnRH or ECP) on ovarian follicular dynamics, luteal function, and pregnancies per AI (P/AI) in Holstein cows receiving timed artificial insemination (TAI). On Day 0, 742 cows in a total of 782 breedings, received 2mg of estradiol benzoate (EB) and one intravaginal progesterone (P4) insert (CIDR). On Day 8, the CIDR was removed, and all cows were given PGF2 alpha and assigned to one of four treatments in a 2 x 2 factorial arrangement: (1) CG: GnRH 48 h later; (2) CE: ECP; (3) EG: eCG+GnRH 48 h later; (4) EE: eCG+ECP. There were significant interactions for eCG x ovulatory stimulus and eCG x BCS. Cows in the CG group were less likely (28.9% vs. 33.8%; P<0.05) to become pregnant compared with those in the EG group (odds ratio [OR]=0.28). There were no differences in P/AI between CE and EE cows (30.9% vs. 29.1%; OR=0.85; P=0.56), respectively. Thinner cows not receiving eCG had lower P/AI than thinner cows receiving eCG (15.2% vs. 38.0%; OR=0.20; P<0.01). Treatment with eCG tended to increase serum progestesterone concentrations during the diestrus following synchronized ovulation (P<0.10). However, the treatment used to induce ovulation did not affect CL volume or serum progesterone concentrations. In conclusion, both ECP and GnRH yielded comparable P/AI. However, eCG treatment at CIDR removal increased pregnancy rate in cows induced to ovulate with GnRH and in cows with lower BCS.

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

“…In the Holstein breed, the diameter of the ovulatory follicle in the control group and the group treated with an average of 400 IU of eCG injected upon removal of the CIDR® were, respectively, 13.1±0.6 mm and 14.7±0.6 mm. This difference was primarily observed in animals presenting a weaker body condition (Souza et al 2009). Similarly, the effect of eCG is more obvious in cattle with higher milk production ( Garcia-Ispierto et al 2012) and those over the age of five (Bryan et al 2010).…”

“…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).…”

“…The majority of ovulations observed took place within 72 to 96 h after removal of the CIDR®. It is possible that injecting eCG increases synchronisation of ovulation, favouring the use of systematic inseminations (Souza et al 2009;Garcia-Ispierto et al 2012). …”

Exogenous hormonal manipulation to increase reproductive efficiency in dairy cows

“…This strategy resulted in greater synchronization of wave emergence, presence of CL during the protocol and greater ovulation rate. Although E2/P4-based protocols (BO et al, 1993) have limitations due to prohibition in some countries, they have been effectively used for FTAI in other countries ( SOUZA et al, 2009;VASCONCELOS et al, 2011;PEREIRA et al, 2013PEREIRA et al, , 2014. Despite been widely used, P4/E2-based FTAI protocols also present a relatively high incidence of ovulation failure, and not optimized P/AI (around 30%) (SOUZA et al, 2009), requiring more studies to understand the cause of these failures in dairy cows.…”

“…Although E2/P4-based protocols (BO et al, 1993) have limitations due to prohibition in some countries, they have been effectively used for FTAI in other countries ( SOUZA et al, 2009;VASCONCELOS et al, 2011;PEREIRA et al, 2013PEREIRA et al, , 2014. Despite been widely used, P4/E2-based FTAI protocols also present a relatively high incidence of ovulation failure, and not optimized P/AI (around 30%) (SOUZA et al, 2009), requiring more studies to understand the cause of these failures in dairy cows. Currently, a 2.0 mg dose of estradiol benzoate (EB) at the onset of the protocol has been used in Nelore (Bos indicus) cattle with good results (MENEGHETTI et al, 2009;PERES et al, 2009;SA FILHO et al, 2009).…”