Yelich J V, Wettemann R P, Marston T T, Spicer L J
Animal Science Department, Oklahoma Agricultural Experiment Station, Stillwater 74078-0425, USA.
Domest Anim Endocrinol. 1996 Jul;13(4):325-38. doi: 10.1016/0739-7240(96)00046-x.
Fall born Angus x Hereford heifers were allotted to treatments at 9 mo of age to achieve the following growth rates: 1) fed to gain 1.36 kg/d (n = 10; HGAIN); and 2) fed to gain 0.23 kg/d for 16 wk, then fed to gain 1.36 kg/d (n = 9; LHGAIN). Growth hormone (GH), insulin-like growth factor-I (IGF-I0, insulin, glucose, nonesterified fatty acids (NEFA), and progesterone were quantified in twice weekly blood samples until onset of puberty. Body weight, hip height, and pelvic area were recorded every 28 d. Frequent blood samples (n = 8 heifers/treatment) were collected every 14 d, commencing on day 29 of treatment until onset of puberty to evaluate secretion of luteinizing hormone (LH) and GH. The HGAIN heifers were younger (369 d; P < 0.001), were shorter at the hip (115 cm; P < 0.05) and had smaller pelvic area (140 cm2; P < 0.10), but body weight (321 kg) did not differ at puberty compared with LHGAIN heifers (460 d; 119 cm; 155 cm2; 347 kg, respectively). The HGAIN heifers had greater (P < 0.05) concentrations of LH, IGF-I, and insulin in serum and glucose in plasma during the first 84 d of treatment than LHGAIN heifers, whereas LHGAIN heifers had greater (P < 0.05) concentrations of GH in serum and NEFA in plasma than HGAIN heifers. On day 68 of treatment, HGAIN heifers had less mean GH (P < 0.01) and greater (P < 0.05) LH pulse frequency than LHGAIN heifers, whereas LH pulse amplitude and mean LH did not differ (P < 0.10) between treatments. Treatment did not influence secretion of LH and GH at 1 and 3 wk before puberty. Mean GH concentrations in serum and GH pulse amplitude in all heifers were greater (P < 0.05) 2 to 9 d (12.9 and 40.7 ng/ml, respectively) than 16 to 23 d (10.4 and 20.0 ng/ml, respectively) before puberty. Nutrient restriction decreased LH pulse frequency and delayed puberty in beef heifers. Furthermore, dramatic changes in mean concentration and amplitude of GH pulses just before puberty in beef heifers may have a role in pubertal development.
秋季出生的安格斯×海福特杂交小母牛在9月龄时被分配到不同处理组，以实现以下生长速度：1）饲喂使其日增重1.36千克（n = 10；高增重组）；2）前16周饲喂使其日增重0.23千克，之后饲喂使其日增重1.36千克（n = 9；低-高增重组）。在青春期开始前，每周采集两次血样，对生长激素（GH）、胰岛素样生长因子-I（IGF-I）、胰岛素、葡萄糖、非酯化脂肪酸（NEFA）和孕酮进行定量分析。每28天记录一次体重、髋高和骨盆面积。从处理第29天开始，每14天采集一次频繁血样（每组8头小母牛），直至青春期开始，以评估促黄体生成素（LH）和GH的分泌情况。高增重组小母牛年龄较小（369天；P < 0.001），髋部较矮（115厘米；P < 0.05），骨盆面积较小（140平方厘米；P < 0.10），但与低-高增重组小母牛（分别为460天、119厘米、155平方厘米、347千克）相比，青春期时体重（321千克）无差异。在处理的前84天，高增重组小母牛血清中的LH、IGF-I和胰岛素以及血浆中的葡萄糖浓度高于（P < 0.05）低-高增重组小母牛，而低-高增重组小母牛血清中的GH和血浆中的NEFA浓度高于（P < 0.05）高增重组小母牛。在处理第68天，高增重组小母牛的平均GH较低（P < 0.01），LH脉冲频率较高（P < 0.05），而处理组之间的LH脉冲幅度和平均LH无差异（P < 0.10）。处理对青春期前1周和3周时LH和GH的分泌没有影响。所有小母牛血清中的平均GH浓度和GH脉冲幅度在青春期前2至9天（分别为12.9和40.7纳克/毫升）高于（P < 0.05）16至23天（分别为10.4和20.0纳克/毫升）。营养限制降低了肉牛小母牛的LH脉冲频率并延迟了青春期。此外，肉牛小母牛青春期前GH脉冲的平均浓度和幅度的显著变化可能在青春期发育中起作用。
