Illius A W, Jessop N S
Division of Biological Sciences, University of Edinburgh, Scotland.
J Anim Sci. 1996 Dec;74(12):3052-62. doi: 10.2527/1996.74123052x.
The weak point in all current methods or models of diet formulation is the prediction of intake. The major uncertainty is not in the cases in which physical constraints apply, but in those in which voluntary intake is limited by feedback from metabolic factors. Voluntary intake is, ultimately, a psychological phenomenon, involving the integration of many signals, and reflects the flexibility of biological systems evolved to cope with variability in food supply, composition and animal state. Conditions giving rise to regulatory signals may provide a framework for modeling metabolic constraints on intake. The empirical evidence for metabolic feedback shows that the animal's productive potential, which affects its ability to utilize nutrients, interacts with the balance of absorbed nutrients to regulate intake. The relative importance of the sites where nutrient imbalance occurs (microbial or host animal metabolism) is unclear, as is the relevant time scale (minutes or days) of response. A model of the effects of asynchrony of nutrient supply to ruminal microbes suggests that ammonia and microbial recycling and the contribution of hind-gut fermentation reduce the asynchrony in the balance of nutrients absorbed into the bloodstream. Hitherto, rather little progress has been made in mathematical modeling of the metabolic processes controlling intake. Models that describe the phenomenon in terms of global variables, such as total energy intake, protein supply, and protein synthetic capacity, can simulate the way constraints may operate without requiring or providing a deeper understanding of the metabolic processes involved. Models describing the flux of energy and materials down established metabolic pathways have the potential to explore constraints on intake, but until the problem of parameterizing such models can be overcome, that potential will remain untapped.
目前所有饮食配方方法或模型的薄弱环节在于摄入量的预测。主要的不确定性并非存在物理限制的情况，而是那些自愿摄入量受代谢因素反馈限制的情况。自愿摄入量最终是一种心理现象，涉及多种信号的整合，反映了生物系统为应对食物供应、组成和动物状态的变化而进化出的灵活性。产生调节信号的条件可能为建立摄入量的代谢限制模型提供一个框架。代谢反馈的实证证据表明，影响动物利用营养物质能力的生产潜力与吸收营养物质的平衡相互作用，从而调节摄入量。营养物质失衡发生的部位（微生物或宿主动物代谢）的相对重要性尚不清楚，反应的相关时间尺度（分钟或天）也是如此。一个关于瘤胃微生物营养供应不同步影响的模型表明，氨、微生物循环利用以及后肠发酵的作用降低了吸收进入血液的营养物质平衡的不同步性。迄今为止，在控制摄入量的代谢过程的数学建模方面进展甚微。用诸如总能量摄入量、蛋白质供应和蛋白质合成能力等全局变量来描述这一现象的模型，可以模拟限制因素可能起作用的方式，而无需或无需深入了解所涉及的代谢过程。描述能量和物质沿既定代谢途径流动的模型有潜力探索对摄入量的限制，但在克服此类模型的参数化问题之前，这种潜力仍将无法发挥。
