Influence of standing estrus before an injection of GnRH during a beef cattle fixed-time AI protocol on LH release, subsequent concentrations of progesterone, and steriodogenic enzyme expression

https://doi.org/10.1016/j.domaniend.2011.08.002Get rights and content

Abstract

Beef cows that exhibit estrus before fixed-time AI have been reported to have increased pregnancy success and increased concentrations of progesterone during the subsequent estrous cycle. Therefore, these experiments were conducted to evaluate if initiation of standing estrus before an injection of GnRH during a fixed-time AI protocol affected LH pulses, subsequent concentrations of progesterone, and luteal steroidogenic enzyme expression. In Experiments 1 and 2, cows were treated with the CO-Synch protocol (100 μg GnRH day −9, 25 mg PGF day −2, and 100 μg GnRH day 0) and allotted to one of two treatments: 1) cows that initiated estrus before GnRH on day 0 (estrus; n = 5) or 2) cows that did not initiate estrus and were induced to ovulate by the GnRH on day 0 (no estrus; n = 5). In Experiment 1, blood samples were collected at 15-min intervals from 0 to 6 (bleed 1), 12 to 20 (bleed 2), 26 to 34 (bleed 3), and 40 to 48 (bleed 4) h after GnRH. Daily blood samples were collected for 17 d. Initiation of estrus before the GnRH injection had no effect on LH release or the pattern of progesterone increase; however, cows detected in estrus had overall increased (P = 0.002) concentrations of progesterone compared with cows not in estrus. In Experiment 2, estrus was detected with the HeatWatch system. Location and size of the ovulatory follicle was determined on day 0 by transrectal ultrasonography at time of injection with GnRH. Blood samples were collected on days 3, 4, 5, 7, and 9; luteal tissue was collected on day 10 (n = 4 estrus and n = 9 no estrus) from corpus luteum (CL) originating from similar-sized follicles (13.0 to 16.0 mm). Total cellular RNA was extracted, and relative mRNA levels were determined by real-time reverse transcription PCR and corrected for GAPDH. There was no effect of estrus on CL weight or concentrations of progesterone. In addition, there was no effect of estrus, follicle size, or CL weight on luteal expression of LH receptor, StAR, CYP11A1, or 3βHSD. However, there was a correlation between follicle size and CL weight (P = 0.01; R2 = 0.43); for every increase of 1 mm in follicle size, CL weight increased by 1.5 g. In summary, estrus did not influence release of LH, CL weight, progesterone concentrations, or expression of steriodogenic enzymes. However, as follicle size increased, CL weight increased; therefore, both follicle size and CL weight were associated with progesterone concentrations.

Introduction

An injection of GnRH has been reported to cause ovulation of a large dominant follicle; [1], [2] therefore, it is used at time of insemination in fixed-time artificial insemination (FTAI) protocols to synchronize ovulation [3]. However, some animals exhibit standing estrus, whereas others do not initiate standing estrus before time of FTAI, and animals that initiated estrus within 24 h of FTAI had increased pregnancy rates compared with those that did not [4], [5].

Progesterone is essential for maintenance of pregnancy and embryo survival [6]. One proposed method to increase pregnancy success through increased corpus luteum (CL) function was with an injection of GnRH at time of insemination to increase or extend the LH surge [7], [8]. However, when GnRH was given at time of insemination, there have been conflicting results in the effect on subsequent concentrations of progesterone. Studies have reported an increase [7], decrease [9], [10], or no change [11] in subsequent concentrations of progesterone compared with controls.

Luteinizing hormone has been reported to play an important role in CL development and function [8], [12], [13], and duration of the LH surge may play a role in luteal development, causing a more functional CL to be produced. One of the reasons for variation in the response to GnRH at insemination could be that pulses of LH around the time of ovulation have been reported to be important for early luteal function [12], [13], [14], and the interval from the onset of estrus to GnRH administration affected LH release around the time of ovulation [14]. Therefore, the objectives of these experiments were to determine whether initiation of standing estrus in beef cows before an injection of GnRH during a FTAI protocol affected LH pulses, subsequent concentrations of progesterone, and luteal steroidogenic enzyme expression.

Section snippets

Materials and methods

Two experiments were conducted at the South Dakota State University with the use of Angus-cross nonpregnant, nonlactating, cyclic mature beef cows. All animals were handled according to procedures approved by the South Dakota State University Institutional Animal Care and Use Committee.

Follicle size and concentrations of estradiol

Animals detected in standing estrus had larger ovulatory follicles (15.4 ± 0.76 mm; P = 0.02) than animals not detected in standing estrus (12.1 ± 0.76 mm). No effects of time, treatment, or treatment × time for concentrations of estradiol were observed during the first sampling period of intensive bleeds. Animals detected in standing estrus had 5.34 ± 0.21 pg mL−1 of estradiol, and animals not detected in standing estrus had 5.02 ± 0.21 pg mL−1 of estradiol. This indicates that cows that

Discussion

An injection of GnRH has been reported to cause ovulation of a large dominant follicle; [1], [2] therefore, it is used at time of insemination in FTAI protocols to synchronize ovulation [3]. Synchronized ovulation eliminates the need for animals to exhibit estrus or estrus detection. However, some animals exhibit standing estrus, whereas others do not initiate standing estrus, and animals that initiated estrus within 24 h of FTAI had increased pregnancy rates compared with those that did not [4]

Acknowledgments

This research was supported by the South Dakota Research Support Fund and the South Dakota Agricultural Experiment Station. The authors acknowledge the South Dakota State University Fund to Enhance Scholarly Excellence in Undergraduate Research for financial support, and the use of the SDSU-FGCF supported in part by NSF/EPSCoR grant Number 0091948 and by the State of South Dakota. Mention of a proprietary product does not constitute a guarantee or warranty of the product by South Dakota Agric.

References (36)

  • M.W. Peters et al.

    Timing of final GnRH of the Ovsynch protocol affects ovulatory follicle size subsequent luteal function, and fertility in dairy cows

    Theriogenology

    (2003)
  • J.H. Britt et al.

    Ovulation, estrus and endocrine response after GnRH in early postpartum cows

    J Anim Sci

    (1974)
  • E.J. Schmitt et al.

    Use of a gonadotropin-releasing hormone agonist or human chorionic gonadotropin for timed insemination in cattle

    J Anim Sci

    (1996)
  • G.A. Perry et al.

    Relationship between follicle size at insemination and pregnancy success

    Proc Natl Acad Sci U S A

    (2005)
  • G.A. Perry et al.

    Relationship between size of ovulatory follicle and pregnancy success in beef heifers

    J Anim Sci

    (2007)
  • L.E. McDonald et al.

    Study of corpus luteum ablation and progesterone replacement therapy in cattle

    Am J Vet Res

    (1952)
  • M.O. Mee et al.

    Administration of GnRH at estrus influences pregnancy rates, serum concentrations of LH, FSH, estradiol-17 beta, pregnancy-specific protein B, and progesterone, proportion of luteal cell types, and in vitro production of progesterone in dairy cows

    J Anim Sci

    (1993)
  • M.C. Lucy et al.

    Gonadotropin-releasing hormone at estrus: luteinizing hormone, estradiol, and progesterone during the periestrual and postinsemination periods in dairy cattle

    Biol Reprod

    (1986)
  • Cited by (16)

    • Effect of estradiol preceding and progesterone subsequent to ovulation on proportion of postpartum beef cows pregnant

      2021, Animal Reproduction Science
      Citation Excerpt :

      A major finding of this study was that E2 concentrations before ovulation had a positive effect on proportions of postpartum cows pregnant following embryo transfer; whereas, there was only a positive effect of P4 concentrations after ovulation on proportion of cows pregnant when E2 concentrations before ovulation were relatively low. Plasma E2 concentration preceding ovulation has previously been associated with diameter of the dominant follicle and establishment of pregnancy in cattle when ovulation was induced (Perry et al., 2007; Fields et al., 2012; Atkins et al., 2013; Jinks et al., 2013). Furthermore, plasma E2 concentrations at the time of GnRH-induced ovulation (GnRH2; d 0) were greater in postpartum beef cows that ovulated in response to the first GnRH injection (GnRH1; d -9), likely due to the presence of a physiologically more mature follicle that had developed at a greater rate (Atkins et al., 2010, 2013).

    • Different doses of equine chorionic gonadotropin on ovarian follicular growth and pregnancy rate of suckled Bos taurus beef cows subjected to timed artificial insemination protocol

      2016, Theriogenology
      Citation Excerpt :

      As a result, we observed a linear positive association between the development of the LF diameter and the P/AI in suckled B taurus beef cows. Synchronized females displaying estrus before TAI exhibited a larger dominant follicle and greater P/AI when compared to females that did not display estrus [28–31]. In agreement with these studies, the present results showed that suckled B taurus cows receiving eCG treatment regardless of the dose, in E2-plus P4–based TAI protocols, had a greater proportion of cows displaying estrus, allowing greater pregnancy rate after TAI than non-eCG–treated cows.

    • Effect of estradiol cypionate and amount of progesterone in the intravaginal device on synchronization of estrus, ovulation and on pregnancy rate in beef cows treated with FTAI based protocols

      2014, Animal Reproduction Science
      Citation Excerpt :

      Estrus detection was performed twice daily from PID removal to ovulation. Onset of estrus was determined as the first of three mounts within a 4-h period that lasted 2 s or longer in duration (Fields et al., 2012). To help heat detection, tail paint was applied at the time of device removal, to estimate the amount of tail paint rubbed off by mounts.

    • Manipulation of the proestrous by exogenous gonadotropin and estradiol during a timed artificial insemination protocol in suckled Bos indicus beef cows

      2013, Livestock Science
      Citation Excerpt :

      Furthermore, beef heifers exposed to a longer exposure of E2 during the proestrous, present alterations in the pattern of receptor expression and other proteins associated with the uterine receptivity pregnancy (Bridges et al., 2012). Therefore, the concentration of E2 during the proestrus either from ovarian follicle or exogenous administration could influence the uterine environment and fertility after AI (Allrich, 1994; Fields et al., 2012; Lyimo et al., 2000; Perry et al., 2007; Sá Filho et al., 2011b). In the present study, the multiparous cows had a greater P/AI than the primiparous cows.

    View all citing articles on Scopus
    View full text