Archibeque S L, Burns J C, Huntington G B
Animal Science Department, North Carolina State University, Raleigh 27695, USA.
J Anim Sci. 2002 May;80(5):1344-51. doi: 10.2527/2002.8051344x.
Level of nitrogen (N) intake and ruminally protected methionine supplementation were evaluated in eight Angus growing steers (initial BW 253+/-21 kg, final BW 296+/-21 kg) in a replicated 4+/-4 Latin square design. The steers were fed two endophyte-free tall fescue (Festuca arundinacea) hays that contained 2.2 (LO) or 2.8% (HI) of DM as N and were either supplemented or not with ruminally protected methionine (10 g metabolizable methionine/d). Diets were fed to provide adequate energy for 0.5 kg ADG and sufficient protein for maintenance (LO), or protein to support 0.5 kg ADG (HI). Following at least 14 d of adjustment, N balance was measured for 6 d. Isotopic urea was infused (15N15N-urea, 0.164 mmol urea N/h) via a jugular catheter for 56 h and urine was collected from 48 to 56 h to measure urea kinetics. Jugular blood was collected during the balance trial, and serum was analyzed for serum urea N (SUN). By design, daily N intake was greater (P < 0.05) for HI (112 g) than for LO (89 g). Compared with LO, steers when fed HI had greater (P < 0.05) daily DMI (4,217 vs 4,151 g), fecal N (34.4 vs 31.2 g), N digested (77.1 vs 57.7 g), urine N (48.3 vs 37.5 g), urine urea N excretion (34.6 vs 24.8 g), and N retained (29.8 vs 21.1 g). When fed HI steers also had higher (P < 0.05) urine urea N concentration (276 vs 219 mM), SUN (8.7 vs 6.7 mM), N digestibility (69.1 vs 64.9%), percentage of urinary N present as urea (71.5 vs 66.7%, P < 0.053), and rate of urea N production (59.6 vs 49.2 g/d) but lower (P < 0.05) percentage of urea N produced that was returned to the ornithine cycle (15.03 vs 19.2 1%) than when fed LO. Methionine supplementation decreased daily urine N (41.2 vs 44.6 g, P = 0.10) and increased both the amount of N retained daily (27.9 vs 23.7 g, P < 0.089) and the percentage of N digested that was retained (40.4 vs 34.6%, P < 0.094). In summary, supplemental methionine met a specific dietary limitation by increasing the amount of digested N that was retained by the steers.
在一项重复的4×4拉丁方设计中，对8头安格斯生长阉牛（初始体重253±21千克，最终体重296±21千克）的氮（N）摄入量水平和瘤胃保护性蛋氨酸补充情况进行了评估。给阉牛饲喂两种内生真菌-free的高羊茅（Festuca arundinacea）干草，其干物质中氮含量分别为2.2%（低水平，LO）或2.8%（高水平，HI），并且要么补充瘤胃保护性蛋氨酸（10克可代谢蛋氨酸/天），要么不补充。日粮的饲喂量能为0.5千克的日增重提供充足能量以及维持所需的足够蛋白质（低水平），或者为0.5千克的日增重提供支持所需的蛋白质（高水平）。在至少14天的适应期后，测量6天的氮平衡。通过颈静脉导管输注同位素尿素（15N15N-尿素，0.164毫摩尔尿素氮/小时），持续56小时，并在48至56小时收集尿液以测量尿素动力学。在平衡试验期间采集颈静脉血，并分析血清中的血清尿素氮（SUN）。按照设计，高水平组（112克）的每日氮摄入量高于低水平组（89克）（P<0.05）。与低水平组相比，高水平组阉牛的每日干物质采食量更高（4217克对4151克，P<0.05）、粪便氮更高（34.4克对31.2克）、消化氮更高（77.1克对57.7克）、尿液氮更高（48.3克对37.5克）、尿尿素氮排泄量更高（34.6克对24.8克）以及氮保留量更高（29.8克对21.1克）。高水平组阉牛的尿尿素氮浓度也更高（276毫摩尔对219毫摩尔，P<0.05）、SUN更高（8.7毫摩尔对6.7毫摩尔）、氮消化率更高（69.1%对64.9%）、尿液氮中以尿素形式存在的百分比更高（71.5%对66.7%，P<0.053）以及尿素氮生成速率更高（59.6克/天对49.2克/天），但与低水平组相比，高水平组返回鸟氨酸循环的尿素氮生成百分比更低（15.03%对19.21%，P<0.05）。补充蛋氨酸可降低每日尿液氮（41.2克对44.6克，P = 0.10），并增加每日氮保留量（27.9克对23.7克，P<0.089）以及消化氮的保留百分比（40.4%对34.6%，P<0.094）。总之，补充蛋氨酸通过增加阉牛保留的消化氮量，满足了特定的日粮限制。
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