Zinn R A, Shen Y
Desert Research and Extension Center, University of California, El Centro 92243, USA.
J Anim Sci. 1998 May;76(5):1280-9. doi: 10.2527/1998.7651280x.
Ruminally degradable intake protein (DIP) and metabolizable indispensable amino acid (MIAA) requirements of feedlot steers were evaluated. Dietary treatments consisted of isocaloric 80% concentrate steam-flaked corn-based diets containing either .8% urea, 1.5% fish meal (FM), 3.0% FM, 4.5% FM, or 4.5% soybean meal (SBM). Treatment effects on characteristics of ruminal and total tract digestion were evaluated using four Holstein steers (249 kg) with cannulas in the rumen and proximal duodenum. Ruminal digestibility of OM (RDOM; P < .05) and feed N (P < .01) and microbial N flow (MNF; P < .01) to the small intestine were greater with urea as the supplemental N source. The level of DIP was closely associated (R2 = .89) with MNF. Postruminal digestibility of OM was greater (P < .05) for FM than for urea-supplemented diets, compensating for lower RDOM. There were no treatment effects (P > .10) on DOM. As the level of FM was increased, MIAA increased linearly (P < .01). Intestinal MIAA were similar (P > .10) for urea- and SBM-supplemented diets. Treatment effects on 56-d growth performance were evaluated using 100 medium-framed crossbred steers (231 kg). Daily weight gain (linear effect; P < .01), DM intake (linear effect; P < .10), feed efficiency (linear effect; P < .05), and diet NE (linear effect; P < .05) increased with level of FM supplementation. Daily weight gain (P < .10) and DM intake (P < .05) were greater for urea- than for SBM-supplemented diets. Using bovine tissue as the reference protein, the biological value (based on chemical score) of the intestinal chyme protein averaged 73%; methionine was first-limiting. There was a close association (R2 = .99) between methionine supply to the small intestine and observed/expected dietary NE. The metabolizable methionine requirement (MMETR, g/d) of medium-framed feedlot steers can be reliably predicted from measures of BW and ADG (MMETR = 1.565 + .0234ADG[268 - (29.4 x .0557BW(.75)ADG(1.097))/ADG] + .0896BW(.75)). There was a very close association (R2 = .89) between DIP and MNF (MNF = 13.7DIP - .66DIP(2) + 25.9). At maximal observed synthesis, DIP accounted for 76% of the MNF. A minimum of 100 g DIP/kg of total tract digestible OM was required to maximize RDOM and MNF.
对育肥牛瘤胃可降解摄入蛋白（DIP）和代谢不可缺少氨基酸（MIAA）的需求进行了评估。日粮处理包括等热量的、以80%蒸汽压片玉米浓缩料为基础的日粮，分别含有0.8%尿素、1.5%鱼粉（FM）、3.0%FM、4.5%FM或4.5%豆粕（SBM）。使用4头安装有瘤胃和十二指肠近端瘘管的荷斯坦牛（体重249千克）评估处理对瘤胃和全消化道消化特性的影响。以尿素作为补充氮源时，瘤胃有机物质消化率（RDOM；P < 0.05）、饲料氮消化率（P < 0.01）以及小肠微生物氮流量（MNF；P < 0.01）更高。DIP水平与MNF密切相关（R2 = 0.89）。FM的瘤胃后有机物质消化率高于补充尿素的日粮（P < 0.05），弥补了较低的RDOM。对可消化有机物质（DOM）没有处理效应（P > 0.10）。随着FM水平的提高，MIAA呈线性增加（P < 0.01）。补充尿素和SBM的日粮的小肠MIAA相似（P > 0.10）。使用100头中等体格的杂交牛（体重231千克）评估处理对56天生长性能的影响。随着FM补充水平的提高，日增重（线性效应；P < 0.01）、干物质摄入量（线性效应；P < 0.10）、饲料效率（线性效应；P < 0.05）和日粮净能（线性效应；P < 0.05）均增加。补充尿素的日粮的日增重（P < 0.10）和干物质摄入量（P < 0.05）高于补充SBM的日粮。以牛组织作为参考蛋白，小肠食糜蛋白的生物学价值（基于化学评分）平均为73%；蛋氨酸是第一限制性氨基酸。小肠蛋氨酸供应量与观察到的/预期的日粮净能之间存在密切关联（R2 = 0.99）。中等体格的育肥牛的代谢蛋氨酸需求量（MMETR，克/天）可以根据体重（BW）和平均日增重（ADG）可靠地预测（MMETR = 1.565 + 0.0234ADG[268 - (29.4 × 0.0557BW(0.75)ADG(1.097))/ADG] + 0.0896BW(0.75)）。DIP与MNF之间存在非常密切的关联（R2 = 0.89）（MNF = 13.7DIP - 0.66DIP2 + 25.9）。在观察到的最大合成量时，DIP占MNF的76%。为使RDOM和MNF最大化，每千克全消化道可消化有机物质至少需要100克DIP。
