Velayudhan B T, Govoni K E, Hoagland T A, Zinn S A
Department of Animal Science, University of Connecticut, Storrs 06269, USA.
J Anim Sci. 2007 Nov;85(11):2866-72. doi: 10.2527/jas.2007-0281. Epub 2007 Aug 20.
To determine the effects of bovine somatotropin (bST) treatment beginning at 3 ages on the growth rate and components of the somatotropic axis, 40 beef cattle (200 +/- 21 d of age) were randomly assigned to 1 of 4 treatments (10 animals/treatment). Three of the treatment groups received bST (33 mug/kg of BW) daily beginning at 200, 250, or 300 d of age until all animals reached 400 d of age; the fourth group served as controls (0 bST). Animals were housed in pens (5 animals per pen; 2 pens per treatment) and fed a diet formulated for an ADG of 1.2 kg/d. Feed intake (per pen) was measured daily, and BW was determined weekly. Blood samples (10 mL) and ultrasound measurements were collected at 200, 250, 300, 350, and 400 d of age. Serum concentrations of ST and IGF-I were determined by RIA and IGFBP-2 and -3 by ligand blot procedures. Overall, cattle gained 284.0 +/- 14.7 kg of BW with a treatment x week interaction (P < 0.01), such that during the treatment period ADG was 11.6, 8.7, and 15.8% greater (P < 0.05) in cattle treated with bST beginning at 200, 250, and 300 d, respectively, relative to controls during the same time frame. Average DMI was 13.6% less (P < 0.05) in bST-treated cattle than in controls. Increases in ADG coupled with a reduction in DMI resulted in 11.7, 14.0, and 26.4% increases (P < 0.01) in the efficiency of gain (G:F) in bST-treated cattle beginning at 200, 250, and 300 d of age, respectively, compared with contemporary controls. Backfat thickness increased (P < 0.05) over time, but the magnitude of the increase was less in the bST-treated cattle (treatment x week interaction; P < 0.05). Area of the LM increased (P < 0.05) over time but was similar across treatment groups. Serum concentrations of ST, IGF-I, and IGFBP-3 increased (P < 0.05), whereas IGFBP-2 decreased (P < 0.05) over time. The changes in the components of somatotropic axis were more pronounced in bST-treated cattle compared with controls, with the greatest magnitude of response in animals that began bST treatment at 300 d of age. In conclusion, the exogenous bST-induced growth response was greater in animals that began to receive bST administration at 300 d of age and received it for a shorter period (100 d) compared with animals that received bST beginning at 200 or 250 d of age.
为了确定在3个年龄开始使用牛生长激素（bST）处理对生长速率和生长激素轴组成部分的影响，将40头肉牛（200±21日龄）随机分配到4种处理中的1种（每组10头动物）。其中3个处理组从200、250或300日龄开始每天接受bST（33μg/kg体重），直到所有动物达到400日龄；第四组作为对照组（不使用bST）。动物被饲养在栏舍中（每栏5头动物；每种处理2栏），并饲喂一种为日增重1.2kg/d配制的日粮。每天测量采食量（每栏），每周测定体重。在200、250、300、350和400日龄采集血样（10mL）并进行超声测量。通过放射免疫分析法测定血清生长激素（ST）和胰岛素样生长因子-I（IGF-I）的浓度，通过配体印迹法测定胰岛素样生长因子结合蛋白-2（IGFBP-2）和-3（IGFBP-3）的浓度。总体而言，肉牛体重增加了284.0±14.7kg，存在处理×周的交互作用（P<0.01），因此在处理期，相对于同期对照组，从200、250和300日龄开始使用bST处理的肉牛日增重分别高出11.6%、8.7%和15.8%（P<0.05）。bST处理的肉牛平均干物质采食量比对照组低13.6%（P<0.05）。日增重增加且干物质采食量减少，使得从200、250和300日龄开始使用bST处理的肉牛，与同期对照组相比，增重效率（生长育肥比）分别提高了11.7%、14.0%和26.4%（P<0.01）。随着时间推移，背膘厚度增加（P<0.05），但bST处理的肉牛增加幅度较小（处理×周的交互作用；P<0.05）。随着时间推移，腰大肌面积增加（P<0.05），但各处理组之间相似。随着时间推移，血清ST、IGF-I和IGFBP-3浓度增加（P<0.05），而IGFBP-2浓度降低（P<0.05）。与对照组相比，bST处理的肉牛生长激素轴组成部分的变化更为明显，在300日龄开始bST处理的动物中反应程度最大。总之，与从200或25日龄开始接受bST的动物相比，在300日龄开始接受bST处理且处理时间较短（100天）的动物中，外源性bST诱导的生长反应更大。
