Jones E J, Armstrong J D, Harvey R W
Physiology Program, North Carolina State University, Raleigh 27695-7621.
J Anim Sci. 1991 Apr;69(4):1607-15. doi: 10.2527/1991.6941607x.
We determined changes in insulin, glucose, free fatty acids (FFA), growth hormone (GH), insulin-like growth factor I (IGF-I) and LH before puberty in Angus, Braford, Charolais, and Simmental heifers. Our primary objective was to identify metabolites and metabolic hormones that serve as metabolic cues for onset of puberty. Angus (n = 12). Braford (n = 7), Charolais (n = 9), and Simmental (n = 7) heifers were assigned at weaning (289 +/- 25 d of age; 264 +/- 23 kg) to open-sided pens with slotted floors, and they were fed a corn silage-concentrate diet formulated to provide gains of .91 kg/d. Puberty was defined as the 1st d (d 0) that serum progesterone (determined in blood samples collected at weekly intervals) exceeded 1 ng/ml. Blood samples were collected before and after feeding at 15-min intervals for 8 h at 21-d intervals before puberty in a subsample of heifers (at least five per breed). Angus and Simmental heifers weighed less and were younger (P less than .05) at puberty than Charolais and Braford heifers. Serum FFA before feeding and frequency of LH release increased (P less than .05) from d-40 +/- 3 to d-17 +/- 3 in all breeds. Conversely, concentrations of insulin were greater (P less than .05) at -40 than at -17 d from puberty in Angus, but not in Braford, Charolais, or Simmental heifers. Frequency of GH release was greater at d -40 than at d -17 in Angus heifers; however, in Braford and Charolais heifers frequency of GH release was greater at d -17 than at d -40. Concentrations of IGF-I (measured every 2 wk) increased linearly (P less than .07) from d -56 to 0 from puberty in Angus but not in other breeds. In conclusion, frequency of LH release and concentrations of FFA increased before puberty in all breeds; however, consistent changes in other metabolites and hormones were observed only in Angus heifers.
我们测定了安格斯、布拉福德、夏洛来和西门塔尔小母牛青春期前胰岛素、葡萄糖、游离脂肪酸（FFA）、生长激素（GH）、胰岛素样生长因子I（IGF-I）和促黄体生成素（LH）的变化。我们的主要目标是确定作为青春期开始代谢信号的代谢物和代谢激素。安格斯（n = 12头）、布拉福德（n = 7头）、夏洛来（n = 9头）和西门塔尔（n = 7头）小母牛在断奶时（年龄289±25天；体重264±23千克）被分配到带缝隙地板的开放式牛舍，饲喂玉米青贮-精料日粮，设计日增重为0.91千克。青春期定义为血清孕酮（每周采集的血样中测定）超过1纳克/毫升的第1天（第0天）。在青春期前，以21天为间隔，对小母牛的一个亚组（每个品种至少5头）每隔15分钟在采食前后采集血样，持续8小时。安格斯和西门塔尔小母牛在青春期时体重比夏洛来和布拉福德小母牛轻且年龄小（P < 0.05）。在所有品种中，采食前血清FFA和LH释放频率从第-40±3天到第-17±3天增加（P < 0.05）。相反，安格斯小母牛青春期前-40天时胰岛素浓度比-17天时高（P < 0.05），但布拉福德、夏洛来或西门塔尔小母牛并非如此。安格斯小母牛第-40天时GH释放频率比第-17天时高；然而，布拉福德和夏洛来小母牛第-17天时GH释放频率比第-40天时高。安格斯小母牛青春期前从第-56天到第0天，IGF-I浓度（每2周测定一次）呈线性增加（P < 0.07）而其他品种并非如此。总之，所有品种在青春期前LH释放频率和FFA浓度均增加；然而，仅在安格斯小母牛中观察到其他代谢物和激素的一致变化。
