动物营养学报    2022, Vol. 34 Issue (3): 1709-1720    PDF    
饲粮蛋白质水平对妊娠期云南半细毛羊氮平衡和养分排放的影响
赵小琪1 , 王思宇1 , 薛白2 , 倪晓君1 , 李银江1 , 洪琼花1     
1. 云南省畜牧兽医科学院, 昆明 650224;
2. 四川农业大学动物营养研究所, 成都 611130
摘要: 本试验旨在研究饲粮蛋白质水平对妊娠期云南半细毛羊氮平衡和氮、磷、钙排放的影响。选取50只体况良好、体重[(46.52±4.58)kg]相近、年龄一致、配种日期相同的经产2胎妊娠期云南半细毛羊,随机分为5组,每组10个重复,每个重复1只羊。5组试验羊在妊娠前期和中期饲喂蛋白质水平分别为6.65%(Ⅰ组)、9.02%(Ⅱ组)、10.97%(Ⅲ组)、12.43%(Ⅳ组)和13.95%(Ⅴ组)的试验饲粮,妊娠后期饲喂蛋白质水平分别为6.31%(Ⅰ组)、7.77%(Ⅱ组)、10.47%(Ⅲ组)、12.69%(Ⅳ组)和15.25%(Ⅴ组)的试验饲粮。从妊娠第46天算起,所有试验羊进行为期104 d的饲养试验,其中预试期14 d,正试期90 d。分别在妊娠前期(妊娠第71~75天)、中期(妊娠第101~105天)和后期(妊娠第131~135天)从各组选5只试验羊进行为期5 d的消化代谢试验。结果表明:1)在妊娠前期,饲粮蛋白质水平对粪干物质排放量、尿磷排放量、尿钙排放量的影响不显著(P>0.05);粪氮排放量、尿氮排放量和氮总排放量随着饲粮蛋白质水平的升高而增加;Ⅴ组的粪磷排放量、磷总排放量显著高于Ⅰ组(P < 0.01);Ⅴ组的粪钙排放量、钙总排放量最高,而Ⅲ组最低。在妊娠中期,粪干物质排放量、尿磷排放量不受饲粮蛋白质水平的显著影响(P>0.05);尿氮排放量、氮总排放量、粪磷排放量、磷总排放量随着饲粮蛋白质水平的升高而增加,Ⅳ的粪氮排放量、粪钙排放量、钙总排放量最高,Ⅰ组的尿钙排放量显著高于其他各组(P < 0.05)。在妊娠后期,饲粮蛋白质水平对粪干物质排放量、尿磷排放量的影响不显著(P>0.05);粪氮排放量、尿氮排放量、氮总排放量、粪磷排放量、磷总排放量、粪钙排放量随着饲粮蛋白质水平的升高而增加。2)妊娠前期和中期云南半细毛羊氮排放以粪中排放为主,而在妊娠后期,当采食氮较低时,氮排放仍然以粪中排放为主,但随着采食氮的增加,尿氮排放量大于粪氮排放量。妊娠期磷、钙排放量几乎都从粪中排放,粪磷占比和粪钙占比分别为98.52%~99.68%和96.22%~98.98%。3)妊娠期云南半细毛羊的采食氮随着饲粮蛋白质水平的升高而增加,妊娠前期和中期的沉积氮则呈先升高后降低趋势,在Ⅳ组最高;妊娠后期沉积氮与饲粮蛋白质水平变化一致,在Ⅴ组最高;整个妊娠期各组云南半细毛羊的氮平衡均为正。综合本试验的结果,以氮沉积率为标识,妊娠前期、中期和后期云南半细毛羊的最佳饲粮蛋白质水平分别为12.43%、12.43%、10.47%,此蛋白质水平时氮沉积效率最佳,粪尿中的氮、磷排放量较少,有利于降低环境污染。
关键词: 云南半细毛羊    妊娠期    蛋白质    氮平衡    养分排放    
Effects of Dietary Crude Protein Level on Nitrogen Balance and Nutrient Excretions of Yunnan Semi-Fine Wool Ewes during Pregnancy
ZHAO Xiaoqi1 , WANG Siyu1 , XUE Bai2 , NI Xiaojun1 , LI Yinjiang1 , HONG Qionghua1     
1. Yunnan Animal Science and Veterinary Institute, Kunming 650224, China;
2. Institute of Animal Nutrition, Sichuan Agricultural University, Chengdu 611130, China
Abstract: This experiment aimed to study the effects of dietary protein level on nitrogen balance and nitrogen, phosphorus and calcium excretions of Yunnan semi-fine wool ewes during pregnancy. Fifty multiparous Yunnan semi-fine wool ewes with good body condition, similar body weight[(46.52±4.58) kg], the same age, and the same mating date were randomly divided into 5 groups with 10 replicates per group and 1 ewe per replicate. The experimental diets with the protein levels of 6.65% (group Ⅰ), 9.02% (group Ⅱ), 10.97% (group Ⅲ), 12.43% (group Ⅳ) and 13.95% (group Ⅴ) were fed in pre- and mid-pregnancy, and the experimental diets with the protein levels of 6.31% (group Ⅰ), 7.77% (group Ⅱ), 10.47% (group Ⅲ), 12.69% (group Ⅳ) and 15.25% (group Ⅴ) were fed in late-pregnancy. From the 46th day of pregnancy and lasted for 104 days, including 14 days preliminary period and 90 days formal period. Five sheep were selected from each group for a 5-day digestion and metabolism trail in pre-pregnancy (the 71st to 75th day of pregnancy), mid-pregnancy (the 101st to 105th day of pregnancy) and late-pregnancy (the 131st to 135th day of pregnancy). The results showed as follows: 1) in pre-pregnancy, dietary protein level had no significant effects on fecal dry matter excretion, urinary phosphorus excretion and urinary calcium excretion (P>0.05); the fecal nitrogen excretion, urinary nitrogen excretion and total nitrogen excretion were increased with the increase of dietary protein level; the fecal phosphorus excretion and total phosphorus excretion of group Ⅴ were significantly higher than group Ⅰ (P < 0.01); the fecal calcium excretion and total calcium excretion of group Ⅴ were the highest and group Ⅲ was the lowest. In mid-pregnancy, fecal dry matter excretion and urinary phosphorus excretion were not significantly affected by dietary protein level (P>0.05); the urinary nitrogen excretion, total nitrogen excretion, fecal phosphorus excretion and total phosphorus excretion were increased with the increase of dietary protein level. Fecal nitrogen excretion, fecal calcium excretion and total calcium excretion of group Ⅳ were the highest, and urinary calcium excretion of group Ⅰ was significantly higher than that of other groups (P < 0.05). In late-pregnancy, dietary protein level had no significant effects on fecal dry matter excretion and urinary phosphorus excretion (P>0.05); the fecal nitrogen excretion, urinary nitrogen excretion, total nitrogen excretion, fecal phosphorus excretion, total phosphorus excretion and fecal calcium excretion were increased with the increase of dietary protein level. 2) In pre- and mid-pregnancy, the nitrogen excretion of Yunnan semi-fine ewes was mainly in feces, while in late-pregnancy, nitrogen excretion was still mainly in feces when the intake of nitrogen was low, but with the increase of the intake of nitrogen, urinary nitrogen excretion was greater than fecal nitrogen excretion. Almost all phosphorus and calcium excretion in feces and urine were discharged from feces during pregnancy, accounting for 98.52% to 99.68% and 96.22% to 98.98% of total phosphorus excretion and total calcium excretion, respectively. 3) The nitrogen intake of Yunnan semi-fine wool ewes during pregnancy was increased with the increase of dietary protein level, and the nitrogen deposition in pre- and mid-pregnancy increased firstly and then decreased, which was the highest in group Ⅳ; the change of nitrogen deposition in late-pregnancy was consistent with the dietary protein level, which was the highest in group Ⅴ; the nitrogen balance of Yunnan semi-fine wool ewes was positive during pregnancy. Based on the results of this experiment, taking the nitrogen deposition rate as the marker, the optimal dietary protein levels of Yunnan semi-fine wool ewes in pre-, mid- and late-pregnancy are 12.43%, 12.43% and 10.47%, respectively. At this protein level, the nitrogen deposition efficiency is the best, and the excretions of nitrogen and phosphorus in feces and urine are less, which is conducive to reducing environmental pollution.
Key words: Yunnan semi-fine wool ewes    pregnancy    protein    nitrogen balance    nutrient excretions    

氮平衡反映的是动物机体氮的摄入和排出的关系,反刍动物氮平衡及养分消化率受饲粮蛋白质水平、营养成分组成、饲养模式、生理阶段等多种因素的影响[1-2]。近年来,国内外研究学者对绵羊、山羊的氮平衡做了许多研究[3-6],但是有关饲粮蛋白质水平对妊娠期绵羊氮平衡及氮、磷排放影响的研究甚少。随着肉羊产业的不断发展,为了快速提高生产性能获得更大的经济效益,在饲粮中添加过量的氮、磷,而多余的氮、磷通过粪尿排放到环境中,是氮、磷排放过多的主要原因。粪尿中的氮最终会以氨、硝酸盐和胺3种形态进入土壤,造成土壤污染,影响空气质量;而粪尿中的磷流入江湖,还会引起水体富营养化,危害水生动、植物的生长[7-8]。目前,在不影响动物生产性能的前提下,从源头控制氮、磷排放的研究已经成为畜禽污染防控的热点之一。研究发现,通过控制饲粮中氮和磷添加量[9-10]、优化氨基酸组成[11]、改良原料加工技术[12]、添加酶制剂[13]等措施可以提高氮、磷利用率,减少氮、磷排放。本试验采用饲养试验和消化代谢试验相结合的方法,通过研究饲粮蛋白质水平对妊娠期云南半细毛羊氮平衡和氮、磷、钙排放的影响,为优化妊娠期云南半细毛羊的饲粮结构、减少环境负荷提供基础数据。

1 材料与方法 1.1 试验设计

本试验在云南省昆明市易兴恒畜牧科技有限公司进行。选取50只体况良好、体重[(46.52±4.58) kg]相近、年龄一致、配种日期相同的经产2胎妊娠期云南半细毛羊,随机分为5组,每组10个重复,每个重复为1只羊。5组试验羊饲喂不同蛋白质水平的试验饲粮。试验饲粮参照我国《肉羊饲养标准》(NY/T 816—2004)进行配制,妊娠前期和中期蛋白质水平分别为6.65%(Ⅰ组)、9.02%(Ⅱ组)、10.97%(Ⅲ组)、12.43%(Ⅳ组)和13.95%(Ⅴ组),妊娠后期蛋白质水平分别为6.31%(Ⅰ组)、7.77%(Ⅱ组)、10.47%(Ⅲ组)、12.69%(Ⅳ组)和15.25%(Ⅴ组),其他营养水平基本保持一致,妊娠前期和中期试验饲粮组成及营养水平见表 1,妊娠后期试验饲粮组成及营养水平见表 2。饲养试验从妊娠第46天算起,共104 d,其中预试期14 d,正试期90 d,妊娠第61~90天、第91~120天和第121~150天分别为妊娠前期、中期和后期。

表 1 妊娠前期和中期试验饲粮组成及营养水平(干物质基础) Table 1 Composition and nutrient levels of experimental diets during pre- and mid-pregnancy (DM basis) 
表 2 妊娠后期试验饲粮组成及营养水平(干物质基础) Table 2 Composition and nutrient levels of experimental diets during late-pregnancy (DM basis) 
1.2 饲养管理

试验开始前对羊舍进行清洁、消毒,并仔细查看代谢笼、食槽以及水槽是否有异常。每天08:00、17:00各饲喂1次,自由饮水。试验开始当天清晨将试验羊空腹称重并分组,紧接着进入14 d的预试期。在预试期内对各组试验羊的采食量做好记录,根据前1天的采食量对第2天饲喂量作出及时调整,以保证料槽内有10%左右的余料。预试期内,试验羊适应环境和试验饲粮,预试期结束后进入为期90 d的正试期。正试期试验羊的饲养管理与预试期一致。

1.3 消化代谢试验

分别在妊娠前期(妊娠第71~75天)、中期(妊娠第101~105天)和后期(妊娠第131~135天)从各组随机选5只试验羊进行为期5 d的消化代谢试验。每天收集粪尿样品,连续收集5 d,并准确记录每只试验羊每天的采食量、排粪量、排尿量。每天收集的鲜粪样混匀后按10%取2份,其中一份按5%的比例加入10%的稀盐酸固氮,用于检测粪中粗蛋白质含量;另一份直接放入自封袋保存,用于检测其他营养成分的含量。每天收集的尿样混匀后取总量的10%并加入10%稀盐酸使pH低于3进行固氮。此外,每天需要采集200 g的饲粮样品,备测营养成分含量。全部样品均需-20 ℃保存备用。

1.4 常规营养成分含量测定

饲粮、粪和尿中的常规营养成分含量参照张丽英[14]主编的《饲料分析及饲料质量检测技术》进行测定。

1.5 计算公式
1.6 统计分析

试验数据用Excel 2010进行初步处理,然后用SPSS 25.0进行单因素方差分析(one-way ANOVA),结果以平均值±标准差表示,以P < 0.05作为差异显著的判定标准,P < 0.01作为差异极显著的判定标准。

2 结果与分析 2.1 饲粮蛋白质水平对妊娠前期云南半细毛羊养分排放的影响

表 3可知,在妊娠前期,饲粮蛋白质水平对粪干物质排放量、尿磷排放量、尿钙排放量的影响不显著(P>0.05)。粪氮排放量、尿氮排放量和氮总排放量随着饲粮蛋白质水平的升高而增加,其中Ⅳ组和Ⅴ组的粪氮排放量极显著高于Ⅰ组(P < 0.01),Ⅴ组的尿氮排放量和氮总排放量极显著高于除Ⅳ组以外的其他各组(P < 0.01)。Ⅰ组的粪磷排放量、磷总排放量极显著低于Ⅳ组和Ⅴ组(P < 0.01)。Ⅴ组的粪钙排放量、钙总排放量最高,而Ⅲ组的最低,Ⅳ组和Ⅴ组的粪钙排放量、钙总排放量极显著高于其他各组(P < 0.01),其他各组间差异不显著(P>0.05)。妊娠前期云南半细毛羊粪尿中的氮、磷、钙排放以粪中排放为主,粪氮、粪磷、粪钙排放量分别占各自总排放量的55.36%~81.15%、99.33%~99.61%和96.54%~98.19%,尿氮、尿磷、尿钙排放量分别占各自总排放量的18.85%~44.64%、0.39%~0.67%和1.81%~3.46%。

表 3 饲粮蛋白质水平对妊娠前期云南半细毛羊养分排放的影响 Table 3 Effects of dietary protein level on nutrient excretions of Yunnan semi-fine wool ewes in pre-pregnancy
2.2 饲粮蛋白质水平对妊娠中期云南半细毛羊养分排放的影响

表 4可知,在妊娠中期,粪干物质排放量、尿磷排放量不受饲粮蛋白质水平的显著影响(P>0.05)。Ⅳ组的粪氮排放量最高,Ⅰ组的粪氮排放量显著低于其他各组(P < 0.05);随着饲粮蛋白质水平的升高,尿氮排放量、氮总排放量逐渐增加,其中Ⅳ组和Ⅴ组的尿氮排放量、氮总排放量极显著高于Ⅰ组和Ⅱ组(P < 0.01)。粪磷排放量、磷总排放量随着饲粮蛋白质水平的升高而增加,其中Ⅳ组的粪磷排放量、磷总排放量显著高于Ⅰ组(P < 0.05)。Ⅳ组的粪钙排放量、钙总排放量最高,Ⅳ组和Ⅴ组的粪钙排放量、钙总排放量极显著高于Ⅲ组(P < 0.01),Ⅰ组的尿钙排放量最高且显著高于Ⅲ组和Ⅳ组(P < 0.05)。妊娠中期云南半细毛羊粪尿中的氮、磷、钙排放以粪中排放为主,粪氮、粪磷、粪钙排放量分别占各自总排放量的55.03%~82.83%、99.29%~99.68%和97.46%~98.98%,尿氮、粪磷、粪钙排放量分别占各自总排放量的17.17%~44.97%、0.32%~0.71%和1.02%~2.54%。

表 4 饲粮蛋白质水平对妊娠中期云南半细毛羊养分排放的影响 Table 4 Effects of dietary protein level on nutrient excretions of Yunnan semi-fine wool ewes in mid-pregnancy
2.3 饲粮蛋白质水平对妊娠后期云南半细毛羊养分排放的影响

表 5可知,在妊娠后期,饲粮蛋白质水平对粪干物质排放量、尿磷排放量的影响不显著(P>0.05)。粪氮排放量、尿氮排放量、氮总排放量、粪磷排放量、磷总排放量、粪钙排放量随着饲粮蛋白质水平的升高而增加。Ⅳ组和Ⅴ组的粪氮排放量极显著高于Ⅰ组(P < 0.01),Ⅴ组的尿氮排放量、氮总排放量极显著高于其他各组(P < 0.01);Ⅳ组和Ⅴ组的粪磷排放量、磷总排放量极显著高于Ⅰ组(P < 0.01),且显著高于Ⅱ组(P < 0.05);Ⅴ组的粪钙排放量极显著高于Ⅰ组和Ⅱ组(P < 0.01),Ⅲ组的尿钙排放量极显著低于除Ⅳ组以外的其他各组(P < 0.01),Ⅴ组的钙总排放量最高且极显著高于Ⅰ组、Ⅱ组和Ⅲ组(P < 0.01)。妊娠后期云南半细毛羊粪氮排放量占总氮排放量的45.42%~77.80%,尿氮占22.20%~54.58%,粪尿中的氮排放量在Ⅰ组~Ⅳ组是以粪中排放为主,在Ⅴ组中则是尿氮排放量大于粪氮排放量;粪尿中的磷、钙排放量主要以粪中排放为主,粪磷、粪钙排放量分别占各自总排放量的98.52%~99.44%和96.22%~98.49%,尿磷、尿钙排放量分别占各自总排放量的0.56%~1.48%和1.51%~3.78%。

表 5 饲粮蛋白质水平对妊娠后期云南半细毛羊养分排放的影响 Table 5 Effects of dietary protein level on nutrient excretions of Yunnan semi-fine wool ewes in late-pregnancy
2.4 饲粮蛋白质水平对妊娠期云南半细毛羊氮平衡的影响

表 6可知,整个妊娠期采食氮随着饲粮蛋白质水平的升高而增加。妊娠前期,Ⅳ组的沉积氮和氮沉积率最高,Ⅳ组和Ⅴ组的沉积氮极显著高于Ⅰ组和Ⅱ组(P < 0.01),Ⅲ组和Ⅳ组的氮沉积率显著高于Ⅰ组(P < 0.05)。妊娠中期,Ⅳ组和Ⅴ组的采食氮极显著高于其他各组(P < 0.01),Ⅳ组的沉积氮最高且极显著高于Ⅰ组和Ⅱ组(P < 0.01),各组的氮沉积率差异不显著(P>0.05)。妊娠后期,Ⅴ组的采食氮最高且极显著高于其他各组(P < 0.01),沉积氮随着饲粮蛋白质水平的升高而增加。整个妊娠期各组氮平衡均为正平衡。

表 6 饲粮蛋白质水平对妊娠期云南半细毛羊氮平衡的影响 Table 6 Effects of dietary protein level on nitrogen balance of Yunnan semi-fine wool ewes in pregnancy
3 讨论 3.1 饲粮蛋白质水平对妊娠期云南半细毛羊养分排放的影响

妊娠母羊从饲粮中摄入的蛋白质不仅要维持自身增长需求,还要满足胎儿及其附属物的生长需要,但摄入过多的蛋白质会造成蛋白质资源的浪费,未被利用的氮通过粪氮和尿氮排放到环境中,又会造成环境污染[15-16]。研究报道,饲粮蛋白质水平是影响羊氮采食量、粪氮和尿氮排放量最直接的因素[17-18]。马铁伟等[19]研究了不同饲喂水平对妊娠期杜湖杂交F1代母羊蛋白质代谢的影响,表明母羊的粪氮、尿氮、沉积氮随着采食氮的增加而增加。李卫娟等[20]研究了空怀期云南半细毛羊在不同饲粮蛋白质水平下的氮排放情况,指出随着饲粮蛋白质水平的升高,尿氮排放量增加。本研究中,尿氮排放量和氮总排放量随着饲粮蛋白质水平的升高而增加,与上述研究结果一致。同时还发现,在妊娠前期和中期,粪氮占比高于尿氮占比,氮排放以粪中排放为主,而在妊娠后期,当采食氮较低时,氮排放仍然以粪中排放为主,但随着采食氮的增加,尿氮排放量会大于粪氮排放量。当饲粮蛋白质水平升高时,妊娠前期、中期、后期粪氮排放量分别升高了52.30%、46.97%、85.54%,而尿氮排放量分别升高了458.53%、461.06%、649.51%,可以看出饲粮氮水平的升高能迅速增加尿氮排放量,而粪氮排放量变化相对较小。因此,适宜的饲粮蛋白质水平有利于减少粪尿中氮的排放量。

钙是动物体内含量最多的矿物元素,据欧阳依娜等[4]报道,空怀期云南半细毛羊钙排放量以粪中排放为主,占钙总排放量的96.98%~98.73%,而尿钙排放量仅占1.27%~3.02%。本研究中,妊娠期云南半细毛羊钙排放量随着饲粮蛋白质水平的升高有上升趋势但变化较小,且以粪中排放为主,粪钙排放量占钙总排放量的96.22%~98.98%,而尿钙排放量则占1.02%~3.78%。磷在动物体内的含量仅次于钙,从粪中排出的磷大部分是代谢的内源磷,占磷总排放量的95%~98%,剩余的通过尿液和乳汁排出[21]。本研究中,磷总排放量随着饲粮蛋白质水平的升高而增加,且以粪中排放为主,与李卫娟等[20]的研究结果一致。当今畜牧业为了提高动物的生产性能而在饲粮中添加过量的氮和磷,不仅会影响动物健康,还会增加环境负担[22]。目前关于氮、磷排放对环境影响的研究集中在奶牛上,对羊的研究甚少。从本研究可以看出,在保证羊对养分的维持需要基础上,可以通过降低饲粮蛋白质水平来减少氮、磷的排放量,减轻环境负担。

3.2 饲粮蛋白质水平对妊娠期云南半细毛羊氮平衡的影响

氮平衡是反映动物机体内蛋白质代谢的重要指标,它比蛋白质消化率更能反映蛋白质的利用效率[23]。彭玉麟等[24]、任万录等[25]研究表明,随着饲粮蛋白质水平的升高,氮采食量也升高。王思宇等[18]研究发现,48~52 kg空怀期云南半细毛羊的采食氮、沉积氮、氮表观消化率随着饲粮蛋白质水平的增加而增加。本研究中,妊娠期云南半细毛羊的氮采食量随着饲粮蛋白质水平的升高而增加,妊娠前期和中期的沉积氮则呈先升高后降低趋势,在12.43%蛋白质水平组最高;妊娠后期沉积氮与饲粮蛋白质水平变化一致,在15.25%蛋白质水平组最高。如果饲粮中的蛋白质不能满足动物所需,适当提高饲粮蛋白质水平有利于提高蛋白质的利用率,但当蛋白质已经能满足动物需要,再提高饲粮蛋白质水平则会降低蛋白质利用率[26]。本试验中,在妊娠前期、中期,沉积氮在饲粮蛋白质水平为12.43%时达到最高,说明该蛋白质水平已经能满足试验羊自身需求,再继续升高蛋白质水平则会造成蛋白质过量,只能排出体外;此外,妊娠前期和中期母羊体内的胎儿及其附属物生长速度缓慢,所需的养分相对较少,而妊娠后期胎儿及其附属物生长较快,母羊需要汲取更多的养分来供给它们[27],所以,相较于妊娠前期和中期,妊娠后期母羊需要更多的饲粮蛋白质来维持体内消化代谢。

4 结论

① 妊娠期云南半细毛羊的粪氮排放量、尿氮排放量、氮总排放量随着饲粮蛋白质水平的升高而增加,磷总排放量、钙总排放量有上升趋势,粪干物质排放量、尿磷排放量不受饲粮蛋白质水平的显著影响。

② 妊娠前期和中期云南半细毛羊氮排放以粪中排放为主,而在妊娠后期,当采食氮较低时,氮排放仍然以粪中排放为主,但随着采食氮的增加,尿氮排放量大于粪氮排放量。妊娠期云南半细毛羊磷、钙几乎都从粪中排放,尿中排放较少。

③ 以氮沉积率为标识,妊娠前期、中期和后期云南半细毛羊的最佳饲粮蛋白质水平分别为12.43%、12.43%、10.47%,此蛋白质水平时氮沉积效率最佳,粪尿中的氮磷排放量较少,有利于降低环境污染。

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