Gobikrushanth M, Dutra P A, Bruinjé T C, Colazo M G, Butler S T, Ambrose D J
Department of Agricultural Food and Nutritional Science, University of Alberta, Edmonton, AB, T6G 2P5 Canada.
Livestock Research and Extension Branch, Alberta Agriculture and Forestry, Edmonton, AB, T6H 5T6 Canada.
J Dairy Sci. 2017 Aug;100(8):6753-6762. doi: 10.3168/jds.2016-12529. Epub 2017 May 30.
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.
主要目标是确定促性腺激素释放激素（GnRH）诱导的促黄体生成素（LH）反应的变异性和重复性。次要目标是评估血浆LH、促卵泡生成素（FSH）、雌二醇（E2）和孕酮（P4）浓度之间的关联。100头泌乳期荷斯坦奶牛（35头初产牛，65头经产牛）最初接受预同步方案（第0天，前列腺素F2α；第3天，GnRH），7天后进行Ovsynch方案（第10天，GnRH；第17天，前列腺素F2α；56小时后，GnRH），并在最后一次GnRH注射后16小时进行定时人工授精。在预同步的GnRH注射前以及Ovsynch的第二次GnRH注射前立即采集血样，以测定血浆LH、FSH和P4的浓度。在上述每次GnRH注射后2小时采集第二份血样，以测定GnRH诱导的LH和FSH浓度。在Ovsynch的第二次GnRH注射前采集的样本中也测定了E2的血浆浓度。符合以下条件的奶牛被排除在分析之外：（1）GnRH注射后0小时的LH浓度高于2小时；（2）出现持续的自发性LH峰；（3）对GnRH无反应；（4）在预同步的GnRH和Ovsynch的第二次GnRH时P4≥0.5 ng/mL。根据预同步的GnRH和Ovsynch的第二次GnRH注射后2小时采集的样本，确定GnRH诱导的LH反应的变异性（变异系数）和重复性[动物间方差/（动物内方差+动物间方差）]。在Ovsynch的第二次GnRH时确定血浆LH、FSH、E2和P4之间的关联。GnRH注射前LH的平均（±标准误）浓度分别为0.5±0.04和0.6±0.03 ng/mL，而在预同步的GnRH和Ovsynch的第二次GnRH注射后2小时，LH的平均浓度分别为9.8±1.0和12.1±0.8 ng/mL。在预同步的GnRH和Ovsynch的第二次GnRH时，GnRH诱导的LH的变异性分别为76.1%和52.1%。预同步的GnRH和Ovsynch评估之间GnRH诱导的LH浓度的重复性估计值为0.10。在Ovsynch的第二次GnRH时，血浆LH浓度与FSH和E2呈正相关（r分别为0.61和0.30），与P4呈负相关（r=-0.46）。总之，GnRH诱导的LH反应高度可变且不可重复，LH浓度与FSH和E2呈正相关，与P4呈负相关。
