Sinclair K D, Sinclair L A, Robinson J J
Scottish Agricultural College, Craibstone Estate, Bucksburn, Aberdeen, UK.
J Anim Sci. 2000 Oct;78(10):2659-69. doi: 10.2527/2000.78102659x.
The ruminal degradability, intake, and metabolism of diets differing in their relative rate of energy and nitrogen release in the rumen were characterized prior to their use in a study of the effects of high peripheral levels of ammonia on reproductive function in cattle. In a 2 x 2 factorial experiment, replicated four times, 16 heifers were offered isocaloric and isonitrogenous diets containing two sources of fermentable carbohydrate, fiber (slow energy release, SE) or starch (fast energy release, FE), and two rates of nitrogen release, which were either synchronous (S) or asynchronous (A) to that of energy release. Throughout the experiment, the amount of feed offered was held constant, at a level equivalent to 1.5 x maintenance. Four ruminally fistulated sheep were used to determine the in situ degradability of these diets. The 16 heifers were bled before feeding at 0800 and at 0900, 1000, 1100, 1200, 1400, and 1600 on d 0 (introduction to dietary treatments) and on d 4, 7, 11, 14, 21, and 28. Diet refusals were recorded at hourly intervals after feeding. The rapidly degradable nitrogen fraction of the SE:A and FE:A diets was greater than that of the SE:S and FE:S diets. Postprandial jugular plasma ammonia levels rose to a peak of around 300 micromol/L in heifers offered the SE:A and FE:A diets but did not rise in heifers offered the SE:S and FE:S diets. All feed offered was consumed within 1 h on diets SE:S and FE:S throughout the experiment. The proportion of feed consumed within 1 h of feeding declined from 100% on d 0 to around 70 and 56% by d 21 for heifers given the SE:A and FE:A diets, respectively. Peak postprandial plasma ammonia levels were accordingly lower, at around 160 micromol/L. Plasma urea levels averaged 7 mmol/L and were unaffected by dietary treatment. High plasma ammonia levels were associated with a suppression in the normal postprandial rise in insulin. There was no significant metabolic adaptation to high-ammonia-generating diets, and heifers given these diets modified their pattern of intake in an apparent attempt to avoid excessively high levels of plasma ammonia.
在将不同瘤胃能量和氮释放相对速率的日粮用于研究高外周血氨水平对牛繁殖功能的影响之前，对其瘤胃降解率、采食量和代谢情况进行了表征。在一项重复4次的2×2析因试验中，给16头小母牛提供等热量和等氮量的日粮，这些日粮含有两种可发酵碳水化合物来源，即纤维（能量缓慢释放，SE）或淀粉（能量快速释放，FE），以及两种氮释放速率，其与能量释放要么同步（S）要么异步（A）。在整个试验过程中，提供的饲料量保持恒定，处于相当于1.5倍维持量的水平。使用4头瘤胃造瘘绵羊来测定这些日粮的原位降解率。在试验第0天（引入日粮处理）以及第4、7、11、14、21和28天，于08:00喂食前以及09:00、10:00、11:00、12:00、14:00和16:00对16头小母牛进行采血。喂食后每隔一小时记录日粮拒食量。SE:A和FE:A日粮的快速降解氮组分高于SE:S和FE:S日粮。给提供SE:A和FE:A日粮的小母牛喂食后，颈静脉血浆氨水平升至约300微摩尔/升的峰值，但给提供SE:S和FE:S日粮的小母牛喂食后该水平未升高。在整个试验过程中，SE:S和FE:S日粮提供的所有饲料均在1小时内被采食。对于给予SE:A和FE:A日粮的小母牛，喂食后1小时内采食的饲料比例从第0天的100%分别降至第21天的约70%和56%。相应地，餐后血浆氨峰值水平较低，约为160微摩尔/升。血浆尿素水平平均为7毫摩尔/升，不受日粮处理影响。高血浆氨水平与正常餐后胰岛素升高受到抑制有关。对产生高氨的日粮没有明显的代谢适应，给予这些日粮的小母牛改变了它们的采食模式，显然是为了避免血浆氨水平过高。
