Characterization of the variability and repeatability of gonadotropin-releasing hormone–induced luteinizing hormone responses in dairy cows within a synchronized ovulation protocol

Abstract

The primary objective was to determine the variability and repeatability of GnRH-induced LH responses. The secondary objective was to evaluate the associations among plasma LH, FSH, estradiol (E2), and progesterone (P4) concentrations. One hundred lactating Holstein cows (35 primiparous, 65 multiparous) were initially subjected to a presynchronization protocol (d 0, PGF; d 3, GnRH) followed 7 d later by Ovsynch (d 10, GnRH; d 17, PGF; 56 h later, GnRH) and timed artificial insemination 16 h after the last GnRH. Blood samples were collected immediately before the GnRH injection of presynchronization and the second GnRH of Ovsynch to determine plasma concentrations of LH, FSH, and P4. A second blood sample was collected 2 h after each of the above GnRH injections to determine GnRH-induced LH and FSH concentrations. Plasma concentrations of E2 were also determined in samples collected immediately before the second GnRH of Ovsynch. Cows that (1) had higher LH concentrations at 0 h than at 2 h after GnRH, (2) showed an ongoing spontaneous LH surge, (3) did not respond to GnRH, and (4) had P4 ≥ 0.5 ng/mL at GnRH of presynchronization and the second GnRH of Ovsynch were excluded from the analysis. The variability (coefficient of variation) and repeatability [between animal variance/(within animal variance + between animal variance)] of GnRH-induced LH response were determined from samples collected 2 h after the GnRH of presynchronization and the second GnRH of Ovsynch. The associations among plasma LH, FSH, E2, and P4 were determined at the second GnRH of Ovsynch. Mean (±SEM) LH concentrations before GnRH were 0.5 ± 0.04 and 0.6 ± 0.03 ng/mL, whereas mean LH concentrations 2 h after GnRH were 9.8 ± 1.0 and 12.1 ± 0.8 ng/mL at GnRH of presynchronization and the second GnRH of Ovsynch, respectively. The variability of GnRH-induced LH was 76.1 and 52.1% at GnRH of presynchronization and the second GnRH of Ovsynch, respectively. The repeatability estimate for GnRH-induced LH concentration between GnRH of presynchronization and Ovsynch assessments was 0.10. Plasma concentrations of LH were positively associated with FSH and E2 (r = 0.61 and 0.30, respectively) and negatively associated with P4 (r = -0.46) at the second GnRH of Ovsynch. In summary, GnRH-induced LH responses were highly variable and unrepeatable, and LH concentrations were positively associated with FSH and E2 and negatively associated with P4.

Detection of urinary luteinizing hormone in Japanese black cows after administration of gonadotropin-releasing hormone

“…This study demonstrated LH urinary excretion in cows after administration of GnRH. A transient increase was observed in urine LH levels following the increase in plasma LH concentrations in all cows tested, and ovulation was confirmed 48 hr after GnRH administration, as per previous reports [6][7][8][9]. In our experiment, the peak urinary LH-urinary creatinine ratio was observed between 3 and 6 hr (median 5 hr) after GnRH administration in each cow, which was approximately 3 hr later than that of the plasma LH concentration.…”

Carryover effects of pre- and postweaning planes of nutrition on reproductive tract development and estrous cycle characteristics in Holstein heifers

“…Samples were placed on ice upon collection and centrifuged at 1,500 × g for 20 min at 4°C, and plasma was harvested and stored at −20°C until being assayed for progesterone (P4). Plasma P4 concentrations were quantified at Endocrine Lab Services (University of Saskatchewan, Saskatoon, SK, Canada) using a commercial solid-phase RIA kit (ImmuChem; MP Biomedicals LLC, Orangeburg, NY) as in Gobikrushanth et al (2017). The intra-assay coefficients of variation averaged 8.6% for low and 13.0% for high reference samples, the interassay coefficients were 11.7% for low (mean = 0.96 ng/mL) and 15.7% for high (mean = 11.40 ng/mL) reference samples, and the assay sensitivity was 0.11 ng/mL.…”