Howard J M, Manzo R, Dalton J C, Frago F, Ahmadzadeh A
Animal and Veterinary Science Department, University of Idaho, P.O. Box 442330, Moscow, ID 83844, USA.
Anim Reprod Sci. 2006 Oct;95(3-4):224-33. doi: 10.1016/j.anireprosci.2005.10.010. Epub 2005 Dec 6.
The objectives of this study were to determine the effect of administration of exogenous GnRH 5days after artificial insemination (AI) on ovarian structures, serum progesterone concentration, and conception rates in lactating dairy cows. In experiment 1, 23 Holstein cows were synchronized using the Ovsynch protocol. Five days after AI (day 0) cows were assigned randomly to receive either saline (saline; n=11) or 100microg GnRH (GnRH; n=12). To examine ovarian structures, ultrasonography was performed on day 1 and every other day beginning on day 5 until day 13. On days 5 and 13 blood samples were obtained to measure serum progesterone concentrations. All cows in the GnRH-treated group developed an accessory corpus luteum (CL), whereas cows in the saline group did not. Mean serum progesterone concentrations did not differ between GnRH and saline groups on day 5 (1.64+/-0.46ng/ml versus 2.04+/-0.48ng/ml). On day 13 serum progesterone concentrations were greater (P<0.05) in the GnRH group compared with saline (5.22+/-0.46ng/ml versus 3.36+/-0.48ng/ml). In experiment 2, 542 lactating cows, at two different commercial dairies, were used to test the effect of administering GnRH 5 days after AI on conception rates. Cows were synchronized and detected for estrus according to tail chalk removal. Cows detected in estrus received AI within 1h after detection of estrus. Five days after AI, cows were assigned randomly to receive either GnRH (n=266) or saline (n=276). Pregnancy status was determined by palpation per rectum of uterine contents approximately 40 days after AI. There was no effect of farm on conception rate. There was no effect of treatment as conception rates did not differ between GnRH and saline groups (26.7% GnRH versus 24.3% saline). Regardless of treatment, days in milk, parity, milk yield, and number of services had no effect on the odds ratio of pregnancy. In summary, the results of this study indicated that GnRH administered 5 days after AI increased serum progesterone by developing an accessory CL but did not improve conception rates in dairy cattle.
本研究的目的是确定人工授精（AI）后5天给予外源性促性腺激素释放激素（GnRH）对泌乳奶牛卵巢结构、血清孕酮浓度和受孕率的影响。在实验1中，23头荷斯坦奶牛采用Ovsynch方案进行同期发情处理。人工授精后5天（第0天），奶牛被随机分配接受生理盐水（生理盐水组；n = 11）或100μg GnRH（GnRH组；n = 12）。为检查卵巢结构，在第1天以及从第5天开始每隔一天直至第13天进行超声检查。在第5天和第13天采集血样以测定血清孕酮浓度。GnRH处理组的所有奶牛均形成了副黄体（CL），而生理盐水组的奶牛未形成。在第5天，GnRH组和生理盐水组的平均血清孕酮浓度无差异（1.64±0.46ng/ml对2.04±0.48ng/ml）。在第13天，GnRH组的血清孕酮浓度高于生理盐水组（P<0.05）（5.22±0.46ng/ml对3.36±0.48ng/ml）。在实验2中，来自两个不同商业奶牛场的542头泌乳奶牛用于测试人工授精后5天给予GnRH对受孕率的影响。奶牛根据尾迹粉笔清除情况进行同期发情处理和发情检测。检测到发情的奶牛在发情检测后1小时内接受人工授精。人工授精后5天，奶牛被随机分配接受GnRH（n = 266）或生理盐水（n = 276）。在人工授精后约40天通过直肠触诊子宫内容物确定妊娠状态。奶牛场对受孕率没有影响。处理对受孕率没有影响，因为GnRH组和生理盐水组的受孕率没有差异（GnRH组为26.7%，生理盐水组为24.3%）。无论处理如何，泌乳天数、胎次、产奶量和输精次数对妊娠优势比均无影响。总之，本研究结果表明，人工授精后5天给予GnRH通过形成副黄体增加了血清孕酮，但并未提高奶牛的受孕率。
