Bossis I, Wettemann R P, Welty S D, Vizcarra J A, Spicer L J, Diskin M G
Department of Animal Science, Oklahoma Agricultural Experiment Station, Stillwater 74078-0425, USA.
J Anim Sci. 1999 Jun;77(6):1536-46. doi: 10.2527/1999.7761536x.
Angus x Hereford heifers were used to determine endocrine and ovarian function preceding nutritionally induced anovulation. Six heifers were fed to maintain body condition score (M), and 12 heifers were fed a restricted diet (R) until they became anovulatory. Starting on d 13 of an estrous cycle, heifers were given PGF2alpha every 16 d thereafter to synchronize and maintain 16 d estrous cycles. Ovarian structures of M and R heifers were monitored by ultrasonography daily from d 8 to ovulation (d 1 of the subsequent cycle) until R heifers became anovulatory. Concentrations of LH and FSH were quantified in serum samples collected every 10 min for 8 h on d 2 and 15 (48 h after PGF2alpha), and estradiol and IGF-I were quantified in daily plasma samples from d 8 to 16 during the last ovulatory cycle (Cycle -2) and the subsequent anovulatory cycle (Cycle -1). During the last two cycles before anovulation, M heifers had 50% larger (P < .0001) ovulatory follicles than R heifers and 61% greater (P < .0001) growth rate of the ovulatory follicles. There was a treatment x cycle x day effect (P < .001) for concentrations of estradiol. The preovulatory increase in estradiol occurred in the R and M heifers during Cycle -2 but only in M heifers during Cycle -1. A treatment x cycle x day effect (P < .05) influenced LH concentrations. During Cycle -2, LH concentrations were similar for M and R heifers, but during Cycle -1, M heifers had greater LH concentrations than did R heifers. Concentrations of FSH were greater (P < .05) in R than M heifers after induced luteolysis when R heifers failed to ovulate. There was a treatment x cycle interaction (P < .05) for IGF-I concentrations, and M heifers had 4.7- and 8.6-fold greater IGF-I concentrations than did R heifers during Cycle -2 and -1, respectively. We conclude that growth rate and diameter of the ovulatory follicle, and concentrations of LH, estradiol, and IGF-I are reduced before the onset of nutritionally induced anovulation in beef heifers.
选用安格斯×海福特小母牛来确定营养诱导无排卵前的内分泌和卵巢功能。6头小母牛饲喂以维持体况评分（M组），12头小母牛饲喂限饲日粮（R组）直至出现无排卵。从发情周期的第13天开始，此后每隔16天给小母牛注射一次PGF2α，以同步并维持16天的发情周期。从第8天至排卵（后续周期的第1天）每天通过超声检查监测M组和R组小母牛的卵巢结构，直至R组小母牛出现无排卵。在第2天和第15天（PGF2α注射后48小时）每隔10分钟采集一次血清样本，持续8小时，对LH和FSH浓度进行定量；在最后一个排卵周期（周期-2）和随后的无排卵周期（周期-1）从第8天至第16天每天采集血浆样本，对雌二醇和IGF-I进行定量。在无排卵前的最后两个周期中，M组小母牛的排卵卵泡比R组小母牛大50%（P <.0001），排卵卵泡的生长速度快61%（P <.0001）。雌二醇浓度存在处理×周期×天数效应（P <.001）。在周期-2中，R组和M组小母牛在排卵前雌二醇均升高，但在周期-1中仅M组小母牛出现升高。LH浓度受处理×周期×天数效应影响（P <.05）。在周期-2中，M组和R组小母牛的LH浓度相似，但在周期-1中，M组小母牛的LH浓度高于R组小母牛。在诱导黄体溶解后R组小母牛未排卵时，R组小母牛的FSH浓度高于M组小母牛（P <.05）。IGF-I浓度存在处理×周期交互作用（P <.05），在周期-2和周期-1中，M组小母牛的IGF-I浓度分别比R组小母牛高4.7倍和8.6倍。我们得出结论，在肉用小母牛营养诱导无排卵开始前，排卵卵泡的生长速度和直径以及LH、雌二醇和IGF-I的浓度均降低。
