日粮氮水平对牦牛瘤胃发酵参数和氮组分的影响

 【目的】研究不同氮水平日粮对牦牛瘤胃发酵参数和氮组分的影响。【方法】选用4头体重（148.5±9.2）kg的3岁去势公牦牛，采用4×4拉丁方设计，饲喂4种氮水平日粮：低氮（A：35.92 g•d-1）、中低氮（B：49.44 g•d-1）、中高氮（C：61.28 g•d-1）和高氮（D：72.48 g•d-1）。试验分为4期，每期20 d。在最后1 d，于饲喂前（07：30）和饲喂后（10：00、12：00、14：00和16：00）采集瘤胃液，测定瘤胃液中各发酵指标及氮组分。【结果】日粮不同氮水平处理间牦牛瘤胃pH无显著差异（P＞0.05），肽氨基氮、可溶性蛋白氮、游离氨基氮、总挥发性脂肪酸和氨态氮浓度差异显著（P＜0.05）。氨态氮在不同氮水平日粮和时间交互作用下也有显著差异（P＜0.05）。乙酸/丙酸在氮水平处理下无显著差异（P＞0.05）。【结论】在试验日粮下，当氮水平超过1.97%时，牦牛瘤胃大部分氮组分不再受日粮氮水平的影响，在高氮日粮时乙酸/丙酸最小，总挥发性脂肪酸最高。

Effect of Nitrogen Levels of Diets on Ruminal Fermentation Characters and Nitrogen Fractions in Yak

【Objective】 The objective of this study is to evaluate the effect of different N levels of diets on the ruminal fermentation and nitrogen fractions in yak. 【Method】 Four castrated yaks at (148.5±9.2) kg and 3-year-old of age were used in a partially replicated 4×4 Latin square with 4 different N levels of diets treatments (A(35.92 g•d-1), B(49.44 g•d-1), C(61.28 g•d-1), D (72.48 g•d-1)) and 4 20-day periods. pH, FAA-N (free amino acid nitrogen), NH3-N (NH3 nitrogen), PAA-N (peptide amino acid nitrogen), soluble protein N (nitrogen) and VFA (volatile fatty acid) were studied in different times before (07：30) and after feeding (10：00, 12：00, 14：00, 16：00) at last day. 【Result】 Ruminal pH was not affected by diets (P＞0.05). PAA-N, soluble protein N, FAA-N, total VFA and NH3-N were significantly differed among yaks with different diets (P＜0.05). NH3-N was also affected by diet×time interaction (P＜0.05). Acetate/propionate was not affected by different diets (P＞0.05). 【Conclusion】 Under the rations of the present study, when N of diet greater than 1.97%, most nitrogen fractions in yak do not response to the nitrogen level of the experimental diets. At 2.90% nitrogen of diet, acetate/propionate is the minimum and total VFA is the maximum.