饲粮氮水平对牦牛尿嘌呤衍生物排出量与瘤胃微生物氮产量的影响

Effects of Dietary Nitrogen Level on Urine Purine Derivatives Excretion and Microbial Nitrogen Production in Yaks

本试验旨在探讨牦牛尿中嘌呤衍生物(PD)排出量对饲粮氮水平的响应规律,并基于此估测了瘤胃微生物氮(MN)产量,以期为高寒牧区牦牛的科学饲养提供参考。选取4头体重[(192±12)kg]相近、年龄(3岁)相同的去势公牦牛,采用4×4拉丁方试验设计将牦牛分为4组,各组饲粮氮水平分别是1.03%、1.95%、2.85%和3.76%,每组1头;试验分为4期,每期21 d,包含15 d的预试期和6 d的正试期。结果表明,牦牛尿中PD主要由尿囊素和尿酸组成,尿囊素/PD和尿酸/PD分别为0.69~0.76、0.23~0.30,黄嘌呤与次黄嘌呤的含量极少。当饲粮氮水平升高时,尿中PD、尿囊素、尿酸以及马尿酸排出量均线性增加(P<0.05),而尿酸/PD和嘌呤氮指数(PNI)均线性降低(P<0.05)。瘤胃细菌嘌呤碱基(RNA当量)含量、瘤胃细菌氮含量以及瘤胃MN产量都随着饲粮氮水平升高而线性增加(P<0.05),但饲粮氮用于合成MN的效率[即瘤胃MN/食入氮(NI)]却线性降低(P<0.05)。基于尿中PD排出量(mmol/d)和瘤胃MN产量(g/d)与NI(g/d)之间良好的线性关系,构建了如下数学模型:PD=0.58NI+18.28,MN=0.18NI+22.18。综合得出,当牦牛饲粮氮水平为2.85%时,牦牛瘤胃M N产量最大,为42.60 g/d,而PNI以及饲粮氮用于合成M N的效率却在低氮(1.03%)条件下达到最高,这一结果揭示了牦牛对低氮饲粮中氮素营养高效利用的特点,解释了牦牛对青藏高原饲料营养匮乏的适应性的营养机理。

This experiment w as conducted to explore the regularity of urine purine derivatives（ PD） excretion respond to dietary nitrogen level,and based on this,ruminal microbial nitrogen（ MN） production w as estimated,thus provided references for appropriate feeding of yaks in cold farming area. Four 3-year-old castrated male yaks [body w eight w as（ 192 ± 12） kg] w ere divided into 4 groups w ith 1 yak per group in a 4 × 4 Latin square design. Dietary nitrogen levels of different groups w ere 1. 03%, 1. 95%, 2. 85% and 3. 76%,respectively. The experiment consisted of 4 periods,each lasted for 21 d,allow ing a 15-d pre-test period and a6-d test period. The results show ed that urine PD w ere mainly consist of allantoin and uric acid,allantoin/PD and uric acid/PD w ere 0.69 to 0.76 and 0.23 to 0.30,respectively,and negligible contents of xanthine and hypoxanthine w ere found. As dietary nitrogen level increasing,urine PD,allantoin,uric acid and hippuric acid extractions w ere increased linearly（ P〈0.05）,how ever,uric acid/PD and purine nitrogen index（ PNI） w ere linearly decreased（ P〈0.05）. With the increase of dietary nitrogen level,ruminal bacterial purine bases（ RNA equivalent） content,bacterial nitrogen（ BN） content and MN production w ere linearly increased（ P〈0.05）,and efficiency of dietary nitrogen converted into MN [ruminal MN/nitrogen intake（ NI） ] w as linearly decreased（ P〈0. 05）. There w ere a strong relationship betw een urine PD extraction（ mmol/d）, ruminal MN（ g/d） and NI（ g/d）,the follow ing mathematical equations w ere established as follow s： PD = 0. 58 NI ＋18.28,MN = 0.18 NI＋ 22. 18. In summary,ruminal MN production is the highest（ 42. 60 g/d） w hen dietary nitrogen level is 2.85%,w hereas PNI and efficiency of NI converted into MN are the highest under the condition of low dietary nitrogen level（ 1.03%）. The results indicate the great efficiency of nitrogen utilization w hen low nitrogen provision in yaks,and their adaptation nutrition mechanism to the deficiencies in intake of nutrient of yaks in Tibetan plateau.