Altered progesterone concentrations by hormonal manipulations before a fixed-time artificial insemination CO-Synch + CIDR program in suckled beef cows

Abstract

We hypothesized that pregnancy outcomes may be improved by inducing luteal regression, ovulation, or both (i.e., altering progesterone status) before initiating a timed AI program in suckled beef cows. This hypothesis was tested in two experiments in which cows were treated with either PGF 2 (PG) or PG + GnRH before initiating a timed AI program to increase the proportion of cows starting the program in a theoretical marginal (< 1 ng/mL; Experiment 1) or elevated (≥ 1 ng/mL; Experiment 2) progesterone environment, respectively. The control was a standard CO-Synch + CIDR program employed in suckled beef cows (100 µg GnRH im locations (n = 1,537) were assigned to either: (1) control or (2) PrePG (same as control with a PG injection on study Day −13). The PrePG cows had larger (P < 0.05) follicles on study Day −10 and more (P < 0.05) ovulated after GnRH-1 compared with control cows (60.6 vs. 36.5%), but pregnancy per TAI was not altered (55.5 vs. 52.2%, respectively). In Experiment 2, cows (n = 803) at 4 locations were assigned to: (1) control or (2) PrePGG (same as control with PG injection on study Day −20 and GnRH injection on study Day −17). Although pregnancy per TAI did not differ between control and PrePGG cows (44.0 vs. 44.4%, respectively), cows with BCS > 5.0 or ≥ 77 d postpartum at TAI were more (P < 0.05) likely to become pregnant than thinner cows or those with fewer days postpartum. Presynchronized cows in both experiments were more (P < 0.05) likely than controls to have luteolysis after initial PG injections and reduced (P < 0.05) serum progesterone; moreover, treatments altered the proportion of cows and pregnancy per TAI of cows in various progesterone categories before the onset of the TAI protocol. In combined data from both experiments, cows classified as anestrous before the study but with elevated progesterone on D −10 had increased (P < 0.05) pregnancy outcomes compared with anestrous cows with low progesterone concentrations. Progesterone concentration had no effect on pregnancy outcome of cycling cows. In summary, luteal regression and ovulation were enhanced and progesterone concentrations were altered by presynchronization treatments before the 7-d CO-Synch + CIDR program, but pregnancy per TAI was not improved.3

Impact of Equine Chorionic Gonadotropin Associated with Temporary Weaning, Estradiol Benzoate, or Estradiol Cypionate on Timed Artificial Insemination in Primiparous Bos Indicus Cows

“…The results of the present study showed no differences between treatments applied in three groups of cows to TAI (table 1). However our results (PR) of TAI in primiparous shown to be superior to Sá Filho et al (2009) and Hill et al (2014), which worked with Bos taurus indicus and Bos taurus taurus. On the other hand data from this study confirm very good results in PR when there wasclean up of the bulls for cows previously submitted to P 4 and EB in the end of the breeding season, corroborating studies of Baruselli et al (2012), which found strong increase in PR in cows pretreated with progestin and EB ( Table 1).…”

Role of preovulatory concentrations of estradiol on timing of conception and regulation of the uterine environment in beef cattle

“…At estrus there is also an up-regulation of several genes involved in remodeling of the extracellular matrix (Bauersachs et al 2005), and changes in transcript abundance of inhibin beta A subunit (a member of the TGF-beta signaling pathway) in the bovine intercaruncle area suggests it is involved in coordinating endometrial remodeling (Ishiwata et al 2003). The TGF-beta superfamily is known to be involved in changes in the endometrium, development of the placenta, and maintenance of the pregnancy (Jones et al 2006).…”

“…These protocols are possible since gonadotropin-releasing hormone (GnRH) is capable of inducing ovulation regardless of estrus expression or the corresponding rise in estradiol (Ryan et al 1998). However, induction of ovulation without expression of estrus has been reported to have decreased conception rates (Bridges et al 2012a;Whittier et al 2013;Hill et al 2014) likely from inadequate estrogen concentrations to properly regulate the uterine environment for subsequent sperm transport and gamete-conceptus survival Perry 2008a, 2008b). Thus, cows that did not exhibit standing estrus around the time of GnRH-induced ovulation (± 24 h) had decreased concentrations of estradiol at AI and decreased pregnancy success compared to cows that did exhibit estrus (Perry et al 2005(Perry et al , 2007Richardson et al 2016).…”

Prostaglandin F2α 7 d prior to initiation of the 7-d CO-synch + CIDR protocol failed to enhance estrus response and pregnancy rates in beef heifers

“…In beef heifers, administration of PGF 2α 3 d prior to a TAI protocol increased the percentage of heifers initiating a new follicular wave and increased the synchrony of estrus after controlled internal drug release (CIDR) removal (Grant et al, 2011). Presynchronization with PGF 2α has the potential to improve follicle turnover (Perry et al, 2012;Hill et al, 2014), estrus synchrony (Grant et al, 2011), and pregnancy rates (Perry et al, 2012) in beef cattle.…”