Vestergaard M, Purup S, Frystyk J, Løvendahl P, Sørensen M T, Riis P M, Flint D J, Sejrsen K
Department of Animal Nutrition and Physiology, Danish Institute of Agricultural Sciences, Foulum, DK-8830 Tjele, Denmark.
J Anim Sci. 2003 Sep;81(9):2189-98. doi: 10.2527/2003.8192189x.
Prepubertal Friesian heifer calves (n = 24, initial BW = 195 +/- 5 kg) were assigned to a 2 x 2 factorial block design and used to evaluate the effects of daily GH treatment (0 or 15 mg/d) at either a low or a high feeding level in a 5-wk treatment period on endocrine measurements, hormone receptors, muscle growth, and overall performance. In the pretreatment period, a low feeding level was employed for all calves. During the treatment period, animals at the low feeding level had free access to a roughage-based mixture, whereas animals at the high feeding level had free access to a concentrate mixture and were offered 2 kg/d of the roughage-based mixture. Blood samples were collected weekly starting 3 wk before treatment. Longissimus (LM) and supraspinatus (SS) muscles were obtained at slaughter. Metabolizable energy intake was 81% higher, digestible CP intake was 140% higher, and ADG was 115% higher (all P < 0.001) at the high vs. low feeding level. Feed (DMI, ME, and protein) intake was not affected by GH treatment, but ADG was 18% higher (P < 0.13) in GH-treated than in control heifers at both feeding levels. Although of different magnitudes, the muscle anabolic effects of GH treatment and high vs. low feeding level were additive, and both treatments increased carcass weights (P < 0.02 and P < 0.001, respectively), LM (P < 0.05 and P < 0.001), and SS (P < 0.06 and P < 0.003). The anabolic effect of GH treatment was similar in both muscles, whereas the effect of feeding level was most pronounced in LM. Overall, GH treatment increased plasma GH, IGF-I (both P < 0.001), and IGFBP-3 (P < 0.02); however, GH treatment increased total IGF-I, free IGF-I, and IGFBP-3, and decreased IGFBP-2 mainly at the high feeding level (GH x feeding level interaction; P < 0.02, 0.01, 0.03, and 0.10, respectively). The high feeding level increased insulin, free and total IGF-I, and IGFBP-3 (all P < 0.001), but decreased GH and IGFBP-2 (both P < 0.001). High feeding increased type-1 IGF receptor density (P < 0.02), mainly in LM, in accordance with the largest anabolic response in this muscle, whereas GH treatment had no effect on type-1 IGF receptors. The results suggest that in skeletal muscle, the anabolic effects of exogenous GH are related to endocrine changes in the GH-IGF axis, whereas the effects of feeding level also seem to rely on IGF receptor density in the muscles.
将青春期前的弗里生小母牛犊牛（n = 24，初始体重 = 195±5 kg）分配到一个2×2析因区组设计中，用于评估在为期5周的治疗期内，低或高饲养水平下每日生长激素（GH）处理（0或15 mg/d）对内分泌指标、激素受体、肌肉生长和整体性能的影响。在预处理期，所有犊牛采用低饲养水平。在治疗期，低饲养水平的动物可自由采食基于粗饲料的混合物，而高饲养水平的动物可自由采食精料混合物，并每日提供2 kg基于粗饲料的混合物。从治疗前3周开始每周采集血样。屠宰时获取背最长肌（LM）和冈上肌（SS）。与低饲养水平相比，高饲养水平下的代谢能摄入量高81%，可消化粗蛋白摄入量高140%，平均日增重高115%（所有P < 0.001）。采食量（干物质采食量、代谢能和蛋白质）不受GH处理的影响，但在两个饲养水平下，GH处理的小母牛的平均日增重均比对照高18%（P < 0.13）。尽管程度不同，但GH处理和高与低饲养水平的肌肉合成代谢作用是相加的，两种处理均增加了胴体重（分别为P < 0.02和P < 0.001）、背最长肌（P < 0.05和P < 0.001）和冈上肌（P < 0.06和P < 0.003）。GH处理在两块肌肉中的合成代谢作用相似，而饲养水平的作用在背最长肌中最为明显。总体而言，GH处理增加了血浆GH、胰岛素样生长因子-I（IGF-I，两者P < 0.001）和胰岛素样生长因子结合蛋白-3（IGFBP-3，P < 0.02）；然而，GH处理主要在高饲养水平下增加了总IGF-I、游离IGF-I和IGFBP-3，并降低了IGFBP-2（GH×饲养水平交互作用；分别为P < 0.02、0.01、0.03和0.10）。高饲养水平增加了胰岛素、游离和总IGF-I以及IGFBP-3（所有P < 0.001），但降低了GH和IGFBP-2（两者P < 0.001）。高饲养增加了1型IGF受体密度（P < 0.02），主要在背最长肌中，这与该肌肉中最大的合成代谢反应一致，而GH处理对1型IGF受体没有影响。结果表明，在骨骼肌中，外源性GH的合成代谢作用与GH-IGF轴的内分泌变化有关，而饲养水平的作用似乎也依赖于肌肉中的IGF受体密度。
