Effects of Glutamine on Growth Performance, Nutrient Apparent Digestibility, Rumen Digestive Enzyme Activities and Microbial Counts of Weaned Lambs

REN Jingyu; HAN Yijing; CHEN Zimeng; WANG Xinyao; PEI Caixia

doi:10.12418/CJAN2026.353

2026 , Vol. 38 >Issue 6: 4401 - 4411

DOI: https://doi.org/10.12418/CJAN2026.353

RESEARCH PAPER

Effects of Glutamine on Growth Performance, Nutrient Apparent Digestibility, Rumen Digestive Enzyme Activities and Microbial Counts of Weaned Lambs

REN Jingyu ,
HAN Yijing ,
CHEN Zimeng ,
WANG Xinyao ,
PEI Caixia ^,^*

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College of Animal Science, Shanxi Agricultural University, Jinzhong 030801, China

* professor, E-mail: caixiapeisxnd@163.com

Received date: 2025-09-16

Online published: 2026-06-13

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Abstract

This experiment was conducted to investigate the effects of glutamine (Gln) on growth performance, nutrient apparent digestibility, rumen digestive enzyme activities and microbial counts of weaned lambs. A total of 219 healthy Hu ewe lambs with similar body weight at (45±2) days of age were randomly divided into 4 groups, which were fed pellet feed with 0 (control group), 0.5%, 1.0% and 2.0% Gln added, respectively, along with the same total mixed ration (TMR). The control group was set with 3 replicates (9 lambs in one replicate and 15 lambs in each of the other two replicates), and each experimental group was set with 4 replicates (15 lambs per replicate). Additionally, two Gln addition duration treatments were arranged in each experimental group: 2 replicates with 14-day addition (S group) and the other 2 replicates with long-term addition (60-day addition, L group). Lambs were weaned at about 45 days of age, and the experiment started on the day of weaning with a trial period of 60 days. The results showed as follows: 1) under both 14-day and long-term Gln addition conditions, the average daily gain (ADG) of lambs in the 0.5%, 1.0% and 2.0% Gln groups during days 1 to 60 was significantly higher than that in the control group (P<0.05), with the 2.0% Gln group being the highest; the feed to gain ratio (F/G) during days 1 to 60 was significantly lower than that in the control group (P<0.05), with the 2.0% Gln group being the lowest. The apparent digestibility of dry matter, neutral detergent fiber and acid detergent fiber in the 1.0% and 2.0% Gln groups was significantly higher than that in the control group (P<0.05). The activities of rumen β-glucosidase, α-amylase, pectinase and protease in the 2.0% Gln group were significantly higher than those in the other three groups (P<0.05), and the activity of rumen carboxymethyl cellulase was significantly higher than that in the 0.5% Gln group and control group (P<0.05); the activities of rumen pectinase and protease in the 1.0% Gln group were significantly higher than those in the 0.5% Gln group and control group (P<0.05). The counts of total protozoa and total methanogens in rumen of the 0.5%, 1.0% and 2.0% Gln groups were significantly lower than those in the control group (P<0.05), and the counts of Ruminobacter amylophilus, Ruminococcus albus and Ruminococcus flavefaciens in rumen of the 2.0% Gln group were significantly higher than those in the 0.5% Gln group and control group (P<0.05). 2) When the Gln addition level was 2.0%, compared with the L group, the F/G in the S group during days 1 to 60 was significantly decreased (P<0.05), the crude protein apparent digestibility was significantly increased (P<0.05), the rumen protease activity was significantly increased (P<0.05), and the counts of total protozoa and total methanogens in rumen were both significantly decreased (P<0.05). Additionally, the counts of Ruminococcus albus and Prevotella ruminicola were significantly increased (P<0.05). In conclusion, dietary addition of an appropriate amount of Gln can increase the counts of beneficial rumen microbial populations, digestive enzyme activities and nutrient apparent digestibility of weaned lambs, thereby increasing ADG, decreasing F/G and improving growth performance. Under the conditions of this experiment, the optimal scheme is the combination of 2.0% Gln addition level and 14-day addition duration.

Key words： glutamine; weaned lambs; growth performance; nutrient apparent digestibility; rumen microbiota; digestive enzymes

Cite this article

REN Jingyu , HAN Yijing , CHEN Zimeng , WANG Xinyao , PEI Caixia . Effects of Glutamine on Growth Performance, Nutrient Apparent Digestibility, Rumen Digestive Enzyme Activities and Microbial Counts of Weaned Lambs[J]. Chinese Journal of Animal Nutrition, 2026 , 38(6) : 4401 -4411 . DOI: 10.12418/CJAN2026.353

断奶应激是制约羔羊生长发育的重要因素,常导致采食量下降、肠道屏障功能损伤以及机体免疫力下降等一系列负面效应^[1]。谷氨酰胺(glutamine,Gln)作为一种条件必需氨基酸,不仅能够为小肠、脾脏等组织器官的生长发育提供营养^[2],还参与调节机体能量代谢^[3]、维持酸碱平衡及促进蛋白质合成^[4],并在缓解氧化应激中发挥重要作用^[5-7]。研究表明,在断奶犊牛饲粮中添加Gln可有效改善其免疫状态、抗氧化能力及肠道菌群结构,降低腹泻率,并能显著提高采食量与日增重,进而改善生长性能^[8-9]。另有研究表明,饲粮中添加Gln能够提高断奶仔猪和肉仔鸡的生长性能^[4,10]、增强机体免疫力与抗氧化功能^[6,11],改善肠道结构和酶活性^[12]。断奶应激所引发的负面效应通常在断奶后1~3 d就会出现,且对幼龄动物的生长发育具有长期影响^[13];羔羊断奶3 d时应激反应较大,14 d时有所恢复^[14]。目前生产中多在断奶后2周内补充功能性添加剂(如酸化剂、益生菌等),14 d为常见的短期干预周期。然而,关于Gln短期添加是否足以缓解断奶应激,长期添加是否产生负面效应,目前尚缺乏系统研究。当前关于Gln在羊中的应用研究相对较少,尤其在断奶羔羊中的最佳添加策略(剂量、时长)尚未明确。因此,本研究参考前人在断奶仔猪^[6]和断奶犊牛^[8]方面的研究结果,设置不同添加量(0、0.5%、1.0%和2.0%)和添加时长(14 d和长期添加),探究Gln对断奶羔羊生长性能、养分表观消化率、瘤胃消化酶活性和微生物数量的影响,旨在为Gln在羔羊生产中的科学应用提供理论依据。

1 材料与方法

1.1 试验材料

试验所用Gln为药品级,纯度≥99%。

1.2 试验设计与饲粮

试验动物的使用及管理已获山西农业大学实验动物伦理委员会批准(批准编号:SXAU-EAW-2023S.AB.012021381)。选取219只体重接近、健康状况良好的(45±2)日龄湖羊母羔,随机分为4组,分别饲喂添加0(对照组)、0.5%、1.0%和2.0% Gln的颗粒料,并饲喂相同的全混合日粮(TMR)。对照组设3个重复(其中1个重复9只,其余2个重复各15只);各试验组均设4个重复(15只/重复),且每组内均设置2种Gln添加时长处理:其中2个重复添加14 d(S组),另2个重复长期添加(添加时长60 d,L组)。羔羊于45日龄左右断奶,试验自断奶当天开始,试验期60 d。S组仅在断奶后前14 d添加相应剂量的Gln,14 d后停止添加,继续饲喂基础饲粮直至试验结束;L组从断奶当天起全程添加相应剂量的Gln,持续至试验60 d结束。

基础饲粮由颗粒料(购自英联饲料有限公司)和TMR组成。试验第1~43天饲喂开食料(商品7018DZ),第44天起采用过渡法逐步更换为育成料(商品7117),试验全程饲喂TMR,每天饲喂2次(08:00和17:00),羔羊自由采食和饮水。颗粒料营养水平见表1,TMR组成及营养水平见表2。

表1 颗粒料营养水平(干物质基础)

Table 1 Nutrient levels of the pellet feed (DM basis) %

项目 Items	开食料(第1~43天) Starter feed (days 1 to 43)	育成料(第44~60天) Grower feed (days 44 to 60)
代谢能 ME/(MJ/kg)	10.49	10.93
干物质(风干基础) DM (air-dry basis)	91.12	89.34
粗脂肪 EE	4.87	3.04
粗灰分 Ash	7.64	7.69
粗蛋白质 CP	20.39	19.88
中性洗涤纤维 NDF	33.14	29.18
酸性洗涤纤维 ADF	12.64	8.48
钙 Ca	0.98	1.11
磷 P	0.49	0.60

	代谢能为计算值^[15],其他营养水平为实测值。表2同。
	ME was a calculated value^[15], while the other nutrient levels were measured values. The same as Table 2.

表2 TMR组成及营养水平(干物质基础)

Table 2 Composition and nutrient levels of TMR (DM basis) %

项目 Items	含量 Content
原料 Ingredients
全株玉米青贮 Whole-plant corn silage	58.0
花生秧 Peanut vine	21.0
玉米 Corn	12.0
豆粕 Soybean meal	7.0
麸皮 Wheat bran	1.4
食盐 NaCl	0.3
小苏打 NaHCO₃	0.3
合计 Total	100.0
营养水平 Nutrient levels
代谢能 ME/(MJ/kg)	9.17
干物质(风干基础) DM (air-dry basis)	45.57
粗脂肪 EE	1.69
粗灰分 Ash	10.98
粗蛋白质 CP	8.71
中性洗涤纤维 NDF	45.07
酸性洗涤纤维 ADF	31.64
钙 Ca	0.52
磷 P	0.31

1.3 样品采集与指标测定

1.3.1 饲粮营养成分

颗粒料及TMR中干物质(DM)、粗脂肪(EE)、粗灰分(Ash)、粗蛋白质(CP)、中性洗涤纤维(NDF)、钙(Ca)和磷(P)含量分别参照GB/T 6435—2014、GB/T 6433—2006、GB/T 6438—2007、GB/T 6432—2018、GB/T 20806—2022、GB/T 6436—2018和GB/T 6437—2018进行测定,酸性洗涤纤维(ADF)含量参照NY/T 1459—2022进行测定。

1.3.2 生长性能

于试验第1、14、28和60天晨饲前对羔羊进行空腹称重并记录数据,每天准确记录颗粒料和TMR的投料量与剩料量,计算总干物质采食量(颗粒料+TMR),并参照刘紫萌等^[16]的方法计算平均日采食量(ADFI)、平均日增重(ADG)和料重比(F/G)。

1.3.3 养分表观消化率

于试验第58~60天开展消化试验,同步采集剩料及饲粮样品。消化试验期间,每个重复随机选取5只试验羊,每天进行直肠采粪,将连续3 d采集的鲜粪混匀,取1/4鲜粪加入酒石酸溶液进行固氮处理,经65 ℃烘干、粉碎后备用。饲粮与粪便中DM、Ash、EE、CP、NDF和ADF含量测定方法同1.3.1,有机物(OM)含量通过DM与Ash含量的差值计算得出,盐酸不溶灰分(AIA)含量参照GB/T 23742—2009进行测定。采用内源指示剂(AIA)法计算养分表观消化率,计算公式如下:

某养分表观消化率(%)=[1-(粪便中该养分含量/饲粮中AIA含量)/(饲粮中该养分含量/粪便中AIA含量)]×100。

1.3.4 瘤胃消化酶活性

于试验结束当天晨饲3 h后,每个重复随机选取5只试验羊,通过口腔胃管采集瘤胃液。瘤胃液经4层纱布过滤至50 mL离心管中,立即测定pH,将过滤后的瘤胃液分装,于-80 ℃保存,用于后续指标测定。参照Agarwal等^[17]的方法测定瘤胃液中α-淀粉酶、纤维二糖酶、木聚糖酶、果胶酶、羧甲基纤维素酶和蛋白酶的活性。

1.3.5 瘤胃微生物数量

采用绝对定量PCR法测定上述采集瘤胃液中的微生物数量,瘤胃液DNA的提取、定量PCR的测定方法及所用引物序列参见于天力等^[18]。

1.4 数据统计与分析

试验数据经Excel 2019初步整理后,采用SPSS 22.0软件进行统计。同一Gln添加时长下不同Gln添加量的数据采用单因素方差分析(one-way ANOVA),并用Duncan氏法进行组间多重比较;同一Gln添加量不同添加时长的数据采用t检验分析。结果以“平均值±标准差”表示,P<0.05为差异显著。

2 结果与分析

2.1 Gln对断奶羔羊生长性能的影响

由表3可知,在不同Gln添加量与添加时长下,断奶羔羊采食量均无显著差异(P>0.05)。当Gln添加时长为14 d时,1.0%和2.0% Gln组第28天和第60天体重及第1~14天ADG显著高于对照组(P<0.05),第15~28天、第29~60天及第1~60天ADG显著高于对照组和0.5% Gln组(P<0.05);0.5%、1.0%和2.0% Gln组第1~14天和第15~28天F/G均显著低于对照组(P<0.05);2.0% Gln组第29~60天和第1~60天F/G显著低于其他3组(P<0.05);1.0% Gln组第29~60天和第1~60天F/G显著低于对照组和0.5% Gln组(P<0.05)。当Gln长期添加时,2.0% Gln组第28天和第60天体重和第29~60天ADG显著高于对照组(P<0.05),第15~28天和第1~60天ADG显著高于其他3组(P<0.05),第15~28天F/G显著低于0.5% Gln组和对照组(P<0.05),0.5%、1.0%和2.0% Gln组第29~60天和第1~60天F/G显著低于对照组(P<0.05)。

表3 Gln对断奶羔羊生长性能的影响

Table 3 Effects of Gln on growth performance of weaned lambs

项目 Items	谷氨酰胺添加时长 Gln addition durations/d	谷氨酰胺添加量 Gln addition levels/%
项目 Items	谷氨酰胺添加时长 Gln addition durations/d	0(对照 Control)	0.5	1.0	2.0
体重 BW/kg
第1天 Day 1	14	10.41±1.77	9.26±1.41	9.26±1.42	9.28±1.44
	60	10.41±1.77	10.73±1.61	10.73±1.60	10.74±1.60
第14天 Day 14	14	12.68±2.13	12.59±2.05	12.66±2.18	12.84±1.96
	60	12.68±2.13	13.69±2.14	12.94±2.48	13.28±1.86
第28天 Day 28	14	14.69±2.70^b	15.40±2.97^ab	16.09±2.68^a	16.30±2.23^a
	60	14.69±2.70^b	15.61±2.26^ab	15.52±1.80^ab	16.28±1.53^a
第60天 Day 60	14	20.22±3.68^c	21.27±4.20^bc	22.95±4.01^ab	23.37±2.50^a
	60	20.22±3.68^b	21.89±3.20^a	21.68±2.84^ab	22.75±2.42^a
平均日增重 ADG/(g/d)
第1~14天 Days 1 to 14	14	162.53±74.82^b	237.96±67.79^a	242.46±84.25^Aa	252.68±64.34^Aa
	60	162.53±74.82^b	207.13±83.80^a	158.10±104.26^Bb	181.83±48.96^Bab
第15~28天 Days 15 to 28	14	143.08±63.75^b	200.97±105.21^Ab	245.17±75.59^Aa	246.93±56.92^Aa
	60	143.08±63.75^c	136.76±41.29^Bc	169.31±76.52^Bb	214.43±57.43^Ba
第29~60天 Days 29 to 60	14	197.72±63.23^b	209.33±63.12^b	245.20±68.82^a	252.34±39.75^a
	60	197.72±63.23^b	224.55±67.27^ab	220.00±58.10^ab	231.93±40.25^a
第1~60天 Days 1 to 60	14	175.20±51.89^c	214.43±66.46^b	244.46±58.89^Aa	251.03±34.08^a
	60	175.20±51.89^c	198.31±45.77^b	194.44±41.32^Bb	215.10±22.84^a
颗粒料采食量 Pellet diet intake/(g/d)
第1~14天 Days 1 to 14	14	409.95±10.96	396.61±18.58	436.32±22.02	406.07±19.21
	60	409.95±10.96	437.11±17.85	410.54±16.44	453.36±20.27
第15~28天 Days 15 to 28	14	548.62±13.66	568.75±13.06	655.82±13.63	603.00±11.57
	60	548.62±13.66	632.11±9.35	612.39±10.94	680.32±7.53
第29~60天 Days 29 to 60	14	773.18±15.03	801.50±16.62	915.16±21.81	876.50±18.27
	60	773.18±15.03	832.05±15.19	813.17±18.16	862.61±16.67
第1~60天 Days 1 to 60	14	638.57±14.62	652.72±18.63	742.92±22.40	702.92±21.17
	60	638.57±14.62	693.24±17.58	672.38±18.55	724.58±18.35
全混合日粮采食量 TMR intake/(g/d)
第1~14天 Days 1 to 14	14	124.95±5.69	142.57±8.18	128.32±8.31	132.46±8.42
	60	124.95±5.69	112.14±4.58	103.36±19.46	101.07±5.39
第15~28天 Days 15 to 28	14	151.17±2.15	167.93±2.76	131.64±2.18	140.36±3.16
	60	151.17±2.15	138.07±2.01	129.54±3.03	124.43±6.10
第29~60天 Days 29 to 60	14	131.24±4.13	183.91±4.35	150.11±6.03	146.30±4.77
	60	131.24±4.13	148.06±5.01	144.02±5.45	148.98±6.18
第1~60天 Days 1 to 60	14	134.54±2.71	170.53±3.41	140.72±3.88	141.68±3.31
	60	134.54±2.71	137.35±3.19	131.15±3.44	132.07±4.19
平均日采食量 ADFI/(g/d)
第1~14天 Days 1 to 14	14	535.24±17.02	539.19±38.28	564.69±23.45	538.61±13.55
	60	535.24±17.02	549.23±31.98	513.89±17.24	554.45±81.28
第15~28天 Days 15 to 28	14	699.76±88.67	736.74±47.02	787.39±33.52	743.43±37.83
	60	699.76±88.67	770.26±16.09	741.80±13.99	804.83±43.32
第29~60天 Days 29 to 60	14	905.45±58.22	987.33±67.02	1 067.55±43.09	1 025.03±12.25
	60	905.45±58.22	980.57±20.84	957.61±36.54	1 012.04±15.17
第1~60天 Days 1 to 60	14	773.46±47.27	824.29±55.65	884.85±36.27	845.82±31.55
	60	773.46±47.27	830.85±27.74	803.72±24.45	856.92±37.16
料重比 F/G
第1~14天 Days 1 to 14	14	3.40±0.37^a	2.26±0.06^b	2.33±0.16^b	2.13±0.05^b
	60	3.40±0.37	2.68±0.31	3.26±0.28	3.05±0.05
第15~28天 Days 15 to 28	14	5.18±0.60^a	3.68±0.24^Bb	3.21±0.30^b	3.02±0.33^b
	60	5.18±0.60^a	5.63±0.19^Aa	4.44±0.65^ab	3.79±0.68^b
第29~60天 Days 29 to 60	14	4.74±0.07^a	4.71±0.10^a	4.35±0.04^b	4.06±0.05^c
	60	4.74±0.07^a	4.38±0.18^b	4.35±0.07^b	4.36±0.14^b
第1~60天 Days 1 to 60	14	4.57±0.00^a	3.84±0.01^b	3.62±0.03^Bc	3.36±0.03^Bd
	60	4.57±0.00^a	4.21±0.24^b	4.13±0.06^Ab	3.98±0.19^Ab

对照组在14和60 d添加时长下的数据来自同一批试验动物,重复呈现以便与各Gln添加量组进行同期对比。同行数据肩标不同小写字母表示同一Gln添加时长下不同Gln添加量之间差异显著(P<0.05),同列数据肩标不同大写字母表示同一Gln添加量下不同Gln添加时长之间差异显著(P<0.05)。下表同。

Data for the control group at the Gln addition durations of 14 and 60 d were obtained from the same batch of experimental lambs. The data were presented repeatedly to facilitate concurrent comparison with each Gln addition level group. In the same row, values with different lowercase letter superscripts mean significant differences among different Gln addition levels under the same Gln addition duration (P<0.05); in the same column, values with different uppercase letter superscripts indicate significant differences among different Gln addition durations under the same Gln addition level (P<0.05). The same as below.

当添加0.5%、1.0%和2.0% Gln时,S组第15~28天ADG均显著高于L组(P<0.05);当添加1.0% Gln时,S组第1~60天ADG显著高于L组(P<0.05);当添加1.0%和2.0% Gln时,S组第1~60天F/G显著低于L组(P<0.05)。

2.2 Gln对断奶羔羊养分表观消化率的影响

由表4可知,当Gln添加时长为14 d时,1.0%和2.0% Gln组DM、CP、NDF和ADF表观消化率均显著高于对照组(P<0.05),0.5% Gln组ADF表观消化率显著高于对照组(P<0.05),各组OM和EE表观消化率无显著差异(P>0.05)。当Gln长期添加时,1.0%和2.0% Gln组DM、NDF和ADF表观消化率显著高于0.5% Gln组和对照组(P<0.05),1.0% Gln组CP表观消化率显著高于对照组(P<0.05),各组OM和EE表观消化率无显著差异(P>0.05)。

表4 Gln对断奶羔羊养分表观消化率的影响

Table 4 Effects of Gln on apparent nutrient digestibility of weaned lambs %

项目 Items	谷氨酰胺添加时长 Gln addition durations/d	谷氨酰胺添加量 Gln addition levels/%
项目 Items	谷氨酰胺添加时长 Gln addition durations/d	0(对照 Control)	0.5	1.0	2.0
干物质 DM	14	66.01±5.33^b	66.43±4.93^b	74.53±3.34^a	72.56±0.87^a
	60	66.01±5.33^b	65.90±2.71^b	73.71±4.63^a	70.52±2.73^a
有机物 OM	14	67.94±5.15	68.71±5.11	75.67±3.40	73.97±0.90
	60	67.94±5.15	68.33±2.61	75.50±4.50	72.21±2.65
粗蛋白质 CP	14	74.29±4.59^b	74.48±39.80^b	81.25±2.85^a	79.29±1.09^Aa
	60	74.29±4.59^b	74.74±2.21^b	79.68±3.79^a	76.25±1.82^Bab
粗脂肪 EE	14	79.52±7.66	79.73±12.48	85.08±3.11	80.54±4.86
	60	79.52±7.66	76.62±7.21	84.71±4.04	81.83±6.51
中性洗涤纤维 NDF	14	36.48±11.06^b	38.69±9.60^Ab	51.16±7.01^a	47.49±3.30^a
	60	36.48±11.06^b	34.37±5.49^Bb	51.79±10.01^a	47.15±4.91^a
酸性洗涤纤维 ADF	14	29.67±9.67^c	37.70±7.38^Ab	49.52±6.96^a	42.56±6.60^b
	60	29.67±9.67^b	29.02±5.73^Bb	50.14±10.54^a	43.36±6.29^a

当添加2.0% Gln时,S组CP表观消化率显著高于L组(P<0.05),当添加0.5% Gln时,S组NDF和ADF表观消化率显著高于L组(P<0.05)。

2.3 Gln对断奶羔羊瘤胃消化酶活性的影响

由表5可知,当Gln添加时长为14 d时,2.0% Gln组瘤胃羧甲基纤维素酶、β-葡萄糖苷酶、α-淀粉酶、果胶酶和蛋白酶活性显著高于其他3组(P<0.05),瘤胃木聚糖酶显著高于对照组(P<0.05);1.0% Gln组瘤胃羧甲基纤维素酶、果胶酶和蛋白酶活性显著高于0.5% Gln组和对照组(P<0.05);0.5%和1.0% Gln组瘤胃β-葡萄糖苷酶和α-淀粉酶活性显著高于对照组(P<0.05)。当Gln长期添加时,2.0% Gln组瘤胃β-葡萄糖苷酶、α-淀粉酶、果胶酶、木聚糖酶和蛋白酶活性显著高于其他3组(P<0.05);1.0% Gln组瘤胃β-葡萄糖苷酶、α-淀粉酶、果胶酶、木聚糖酶和蛋白酶活性高于0.5% Gln组和对照组(P<0.05);1.0%和2.0% Gln组瘤胃羧甲基纤维素酶活性显著高于0.5% Gln组和对照组(P<0.05)。

表5 Gln对断奶羔羊瘤胃消化酶活性的影响

Table 5 Effects of Gln on rumen digestive enzyme activities of weaned lambsU/mL

项目 Items	谷氨酰胺添加时长 Gln addition durations/d	谷氨酰胺添加量 Gln addition levels/%
项目 Items	谷氨酰胺添加时长 Gln addition durations/d	0(对照 Control)	0.5	1.0	2.0
羧甲基纤维素酶 Carboxymethyl cellulase	14	0.24±0.07^d	0.36±0.08^c	0.44±0.06^Bb	0.59±0.09^Ba
	60	0.24±0.07^c	0.40±0.06^b	0.75±0.08^Aa	0.79±0.11^Aa
β-葡萄糖苷酶 β-glucosidase	14	0.17±0.04^c	0.37±0.05^Ab	0.38±0.08^b	0.44±0.08^a
	60	0.17±0.04^c	0.22±0.06^Bc	0.32±0.06^b	0.41±0.09^a
木聚糖酶 Xylanase	14	1.55±0.35^b	1.85±0.49^Aab	1.83±0.34^ab	2.04±0.37^a
	60	1.55±0.35^d	1.08±0.17^Bc	1.86±0.23^b	2.57±0.41^a
α-淀粉酶 α-amylase	14	4.28±0.92^c	5.68±0.82^Ab	5.78±0.93^b	8.27±1.17^a
	60	4.28±0.92^c	4.18±0.54^Bc	5.78±0.64^b	7.75±0.96^a
果胶酶 Pectinase	14	1.33±0.41^c	1.21±0.17^Bc	2.16±0.24^Bb	3.15±0.33^a
	60	1.33±0.41^c	1.64±0.30^Ac	2.76±0.26^Ab	3.13±0.34^a
蛋白酶 Protease	14	6.18±1.03^d	8.01±0.96^c	11.09±1.36^b	12.47±1.24^Aa
	60	6.18±1.03^c	7.27±1.81^c	9.76±1.77^b	11.49±1.69^Ba

当添加0.5% Gln时,S组瘤胃β-葡萄糖苷酶、木聚糖酶和α-淀粉酶活性显著高于L组(P<0.05),瘤胃果胶酶活性显著低于L组(P<0.05);当添加1.0% Gln时,S组瘤胃羧甲基纤维素酶和果胶酶活性显著低于L组(P<0.05);当添加2.0% Gln时,S组瘤胃羧甲基纤维素酶活性显著低于L组(P<0.05),瘤胃蛋白酶活性显著高于L组(P<0.05)。

2.4 Gln对断奶羔羊瘤胃微生物数量的影响

由表6可知,当Gln添加时长为14 d时,0.5%、1.0%和2.0% Gln组瘤胃栖瘤胃普雷沃氏菌和总细菌数量显著高于对照组(P<0.05),瘤胃总原虫和总产甲烷菌数量显著低于对照组(P<0.05);2.0% Gln组瘤胃嗜淀粉瘤胃杆菌、白色瘤胃球菌和黄色瘤胃球菌数量显著高于0.5% Gln组和对照组(P<0.05);1.0% Gln组瘤胃白色瘤胃球菌数量显著高于0.5% Gln组和对照组(P<0.05)。当Gln长期添加时,1.0%和2.0% Gln组瘤胃栖瘤胃普雷沃氏菌和总细菌数量显著高于对照组(P<0.05),瘤胃总原虫和总产甲烷菌数量显著低于对照组(P<0.05);2.0% Gln组瘤胃嗜淀粉瘤胃杆菌、白色瘤胃球菌和黄色瘤胃球菌数量显著高于其他3组(P<0.05);1.0% Gln组瘤胃白色瘤胃球菌数量显著高于0.5% Gln组和对照组(P<0.05)。

表6 Gln对断奶羔羊瘤胃微生物数量的影响

Table 6 Effects of Gln on rumen microbial counts of weaned lambs

项目 Items	谷氨酰胺添加时长 Gln addition durations/d	谷氨酰胺添加量 Gln addition levels/%
项目 Items	谷氨酰胺添加时长 Gln addition durations/d	0(对照 Control)	0.5	1.0	2.0
总细菌 Total bacteria/ (×10¹⁰拷贝数/mL)	14	4.91±0.41^c	7.99±1.02^Ab	10.94±3.19^a	11.19±3.29^a
	60	4.91±0.41^c	5.97±1.45^Bbc	7.64±3.54^b	11.07±1.68^a
总原虫 Total protozoa/ (×10¹⁰拷贝数/mL)	14	24.31±4.87^a	4.88±1.56^Bb	1.9±0.38^Bb	3.04±1.90^Bb
	60	24.31±4.87^a	10.51±3.68^Ab	4.46±1.15^Ac	7.18±2.98^Ac
总产甲烷菌 Total methanogens/ (×10⁹拷贝数/mL)	14	7.18±1.36^a	2.64±1.71^Bb	1.74±0.88^Bb	1.63±0.47^Bb
	60	7.18±1.36^a	5.80±1.74^Ab	3.62±1.58^Ac	5.68±2.51^Ab
白色瘤胃球菌 Ruminococcus albus/ (×10⁷拷贝数/mL)	14	1.12±0.28^c	1.47±0.69^c	3.52±2.25^b	10.06±1.37^Aa
	60	1.12±0.28^d	3.29±0.78^c	4.81±0.69^b	9.94±1.03^Ba
黄色瘤胃球菌 Ruminococcus flavefacie- ns/(×10⁷拷贝数/mL)	14	1.13±0.35^b	1.08±0.42^b	0.78±0.17^b	2.31±0.63^a
	60	1.13±0.35^b	1.89±1.33^b	1.04±0.20^b	2.61±0.47^a
嗜淀粉瘤胃杆菌 Ruminobacter amylophil- us/(×10⁶拷贝数/mL)	14	7.22±3.61^b	3.37±1.36^b	4.18±3.44^b	16.83±5.03^a
	60	7.22±3.61^b	6.41±1.76^b	4.90±2.06^b	23.15±5.40^a
栖瘤胃普雷沃氏菌 Prevotella ruminicola/ (×10¹⁰拷贝数/mL)	14	0.55±0.18^c	3.25±0.77^b	3.91±1.59^b	6.84±4.11^Aa
	60	0.55±0.18^c	2.18±0.42^b	2.28±0.45^b	3.91±1.54^Ba

当添加0.5%、1.0%和2.0% Gln时,S组瘤胃总原虫和总产甲烷菌数量均显著低于L组(P<0.05);当添加0.5% Gln时,S组瘤胃总细菌数量显著高于L组(P<0.05);当添加2.0% Gln时,S组瘤胃白色瘤胃球菌和栖瘤胃普雷沃氏菌数量显著高于L组(P<0.05)。

3 讨论

3.1 Gln添加量对断奶羔羊生长性能、养分表观消化率、瘤胃消化酶活性和微生物数量的影响

瘤胃中寄生着细菌、原虫等多种微生物,它们在反刍动物的消化过程中发挥着重要作用。本试验结果表明,在不同添加时长下,饲粮中添加Gln均可剂量依赖性提升瘤胃有益功能菌群的数量,其中2.0% Gln组效果最优,1.0% Gln组次之。栖瘤胃普雷沃氏菌作为瘤胃中参与蛋白质降解的主要细菌^[19],其数量与瘤胃蛋白酶活性呈正相关^[20]。蛋白酶可将饲粮中的蛋白质水解为多肽和氨基酸,供微生物合成菌体蛋白或被动物机体吸收利用^[21]。因此,本试验中2.0% Gln组瘤胃栖瘤胃普雷沃氏菌数量显著增加,瘤胃蛋白酶活性随之升高,CP表观消化率也相应提高。类似地,2.0% Gln组瘤胃白色瘤胃球菌数量较对照组显著增加。该菌株是瘤胃内重要的纤维分解菌,可分泌纤维素酶、木聚糖酶等酶类,与果胶酶协同作用分解饲粮中的粗纤维,将其转化为可被动物利用的小分子糖类,进而提升动物对纤维类饲料原料的利用率^[22];这也与本试验中2.0% Gln组瘤胃果胶酶、木聚糖酶及羧甲基纤维素酶活性显著升高,以及NDF和ADF表观消化率同步提升的结果相印证。此外,本试验中2.0% Gln组瘤胃嗜淀粉瘤胃杆菌数量较对照组显著增加。该菌株作为瘤胃内非结构性碳水化合物的主要降解菌,可分泌淀粉酶、糖化酶等酶类,将大分子碳水化合物快速分解为葡萄糖、短链寡糖等小分子物质,促进动物对碳水化合物的消化吸收^[23],这与本试验中2.0% Gln组瘤胃α-淀粉酶活性显著升高的结果高度契合。

养分表观消化率的提高,有利于增强反刍动物对饲料的利用效率,促进生长发育^[24]。已有研究表明,Gln能够修复肠道上皮组织、改善肠道屏障完整性,从而提高养分表观消化率^[25-27]。幼龄反刍动物消化系统尚未发育完善,断奶阶段面临从液态母乳到固态饲粮的转换,易引发腹泻、消化不良等问题,导致养分利用率降低,进而抑制生长性能,影响养殖经济效益^[28-29]。研究证实,饲粮添加Gln可促进动物生长发育,改善生长性能^[12,30-31]。李梦媛等^[3]研究发现,在哺乳羔羊饲粮中添加Gln可显著提高其ADG,降低F/G;Gln在高精料育肥羔羊^[32]中的应用也取得了一致效果。本试验结果与上述研究相符,在不同添加时长下,2.0% Gln组断奶羔羊第1~60天ADG显著高于对照组,F/G显著低于对照组,证实饲粮中添加适宜剂量的Gln可有效改善断奶羔羊的生长性能。综上所述,饲粮添加Gln可以增加瘤胃有益菌群数量,提高瘤胃消化酶活性,从而提高断奶羔羊对养分的消化利用能力,促进其生长发育,且2.0%为最优添加剂量。

3.2 Gln添加时长对断奶羔羊生长性能、养分表观消化率、瘤胃消化酶活性和微生物数量的影响

本试验结果表明,2.0% Gln添加14 d时,CP表观消化率、瘤胃蛋白酶活性及栖瘤胃普雷沃氏菌数量显著优于长期添加,第1~60天F/G显著低于长期添加;0.5% Gln添加14 d时,NDF、ADF表观消化率、瘤胃β-葡萄糖苷酶和木聚糖酶活性显著优于长期添加。上述结果可能与断奶应激的阶段性特征及Gln的代谢特点有关。断奶应激导致羔羊胃肠道受损,内源Gln消耗加剧,打破原有氨基酸平衡。短期(14 d)添加外源Gln可迅速弥补内源Gln合成不足的缺口,修复受损肠道黏膜,改善消化吸收功能^[33];同时,Gln作为瘤胃微生物的辅助氮源,短期补充可促进微生物增殖,提高蛋白酶、β-葡萄糖苷酶等消化酶活性,间接改善生长性能^[32]。而长期添加时,虽然2.0% Gln组各项指标仍优于对照组,但效果弱于短期添加,这可能是因为:长期外源供给可能反馈抑制机体自身Gln合成能力,形成代谢依赖;Gln与其他必需氨基酸共用同一类转运体,长期添加Gln可能会挤占转运通道,导致其他必需氨基酸的吸收率下降,引发氨基酸代谢失衡^[34]。此外,过量的Gln在瘤胃内被分解菌分解为氨,不仅造成氮源浪费,高浓度氨还可能抑制有益微生物活性^[35],从而影响消化酶活性,削弱长期添加的效果。综上所述,在2.0%最优添加量下,Gln添加14 d效果优于长期添加。

4 结论

饲粮添加适量Gln可提高断奶羔羊瘤胃有益菌群数量、消化酶活性及养分表观消化率,进而提高ADG、降低F/G,改善生长性能。在本试验条件下,2.0%添加量配合14 d添加时长为最优方案。

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