Gerrits W J, Decuypere E, Verstegen M W, Karabinas V
Wageningen Institute of Animal Sciences, Wageningen Agricultural University, The Netherlands.
J Anim Sci. 1998 May;76(5):1356-63. doi: 10.2527/1998.7651356x.
We conducted two experiments with preruminant calves weighing 80 to 240 kg to study the long-term nutritional regulation of circulating IGF-I, thyroxine (T4), and triiodothyronine (T3). The two experiments were similar in design but were performed with calves of two live weight ranges: 80 to 160 kg (Exp. 1) and 160 to 240 kg (Exp. 2). In each experiment, 36 calves were allocated to one of 12 dietary treatments, which consisted of six protein intake levels at each of two energy intake levels. Digestible protein intakes ranged between .90 and 2.72 g N x BW(-.75) x d(-1) in Exp. 1 and between .54 and 2.22 g N x BW(-.75) x d(-1) in Exp. 2. The energy intake levels were kept constant on a protein-free basis; increased energy intakes were realized by increasing energy intake from fat and carbohydrates in a fixed ratio. The digestible protein-free energy intakes were 663 and 851 kJ x BW(-.75) x d(-1) in Exp. 1 and 564 and 752 kJ x BW(-.75) x d(-1) in Exp. 2. Blood samples were taken 5 to 6 h after feeding once every 14 d until the calves reached their target weight. In both experiments, plasma IGF-I and T4 concentrations increased with increasing protein intake (P < .01), but they were unaffected by protein-free energy intake (P > .10). In both experiments, plasma T3 levels were markedly higher at the high protein-free energy intake level (P < .01) and increased slightly with increasing protein intake in Exp. 1 (P = .19) and Exp. 2 (P < .01). Results of these experiments suggest the involvement of IGF-I in the response of protein deposition to increased protein intakes and the involvement of the active thyroid hormone T3 in the response of protein deposition to increased protein-free energy intakes.
我们对体重在80至240千克的反刍前犊牛进行了两项实验，以研究循环中胰岛素样生长因子-I（IGF-I）、甲状腺素（T4）和三碘甲状腺原氨酸（T3）的长期营养调节。这两项实验设计相似，但使用的是两个体重范围的犊牛：80至160千克（实验1）和160至240千克（实验2）。在每个实验中，36头犊牛被分配到12种日粮处理中的一种，每种日粮处理由两个能量摄入水平下的六个蛋白质摄入水平组成。实验1中可消化蛋白质摄入量在0.90至2.72克氮×体重（-0.75）×天（-1）之间，实验2中在0.54至2.22克氮×体重（-0.75）×天（-1）之间。能量摄入水平在无蛋白质基础上保持恒定；通过以固定比例增加脂肪和碳水化合物的能量摄入来实现能量摄入量的增加。实验1中无蛋白质可消化能量摄入量为663和851千焦×体重（-0.75）×天（-1），实验2中为564和752千焦×体重（-0.75）×天（-1）。每隔14天在喂食后5至6小时采集血样，直到犊牛达到目标体重。在两项实验中，血浆IGF-I和T4浓度均随蛋白质摄入量的增加而升高（P < 0.01），但不受无蛋白质能量摄入量的影响（P > 0.10）。在两项实验中，高蛋白无能量摄入水平时血浆T3水平显著更高（P < 0.01），且在实验1（P = 0.19）和实验2（P < 0.01）中随蛋白质摄入量的增加略有升高。这些实验结果表明IGF-I参与了蛋白质沉积对蛋白质摄入量增加的反应，而活性甲状腺激素T3参与了蛋白质沉积对无蛋白质能量摄入量增加的反应。
