Effects of Lamb Milk Replacer on Growth Performance, Apparent Nutrient Digestibility, Rumen Fermentation Parameters, Microflora Structure and Health Status of Leizhou Goats

YANG Xunye; NIU Zhili; WU Qiong; LIU Yingming; LI Xinghua; ZHAO Zhihui; YIN Fuquan; GAO Zhenhua

doi:10.12418/CJAN2023.166

2023 , Vol. 35 >Issue 3: 1758 - 1770

DOI: https://doi.org/10.12418/CJAN2023.166

RESEARCH PAPER

Effects of Lamb Milk Replacer on Growth Performance, Apparent Nutrient Digestibility, Rumen Fermentation Parameters, Microflora Structure and Health Status of Leizhou Goats

YANG Xunye ^,¹ ,
NIU Zhili ¹ ,
WU Qiong ¹ ,
LIU Yingming ¹ ,
LI Xinghua ² ,
ZHAO Zhihui ¹ ,
YIN Fuquan ¹ ,
GAO Zhenhua ^,¹^,^*

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¹ College of Coastal Agricultural Sciences, Guangdong Ocean University, Zhanjiang 524088, China
² Sichuan Tequ Investment Group Co., Ltd., Chengdu 611430, China

*professor, E-mail: xmsgzhh@126.com

Received date: 2022-09-03

Online published: 2023-03-16

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Abstract

This experiment was conducted to investigate the effects of lamb milk replacer on growth performance, nutrient apparent digestibility, rumen fermentation parameters, microflora structure and health status of Leizhou goats. Forty-eight healthy male Leizhou goats with similar body weight at 20 days of age were divided into milk replacer group (fed milk replacer+starter) and milk group (fed milk+starter) with 24 replicates per group and 1 lamb per replicate. The pre-trial period lasted for 10 days and the experimental period lasted for 40 days. The results showed as follows: 1) the average body weight at 40 days of age, as well as the average daily gain and apparent digestibilities of dry matter, crude protein, ether extract and ash of lambs from 21 to 40 days of age in milk replacer group were significantly lower than those in milk group (P<0.05). From 21 to 40 days of age, the starter average daily feed intake in milk replacer group was significantly higher than that in milk group (P<0.05), but the average daily total feed intake was significantly lower than that in milk group (P<0.05), and the diarrhea rate was extremely significantly higher than that in milk group (P<0.01). 2) There were no significant differences in the average body weight at 60 days of age, as well as the average daily gain and nutrient apparent digestibility of lambs from 41 to 60 days of age and 21 to 60 days of age in milk replacer group compared with milk group (P>0.05). The starter average daily feed intake in milk replacer group from 41 to 60 days of age and 21 to 60 days of age was extremely significantly higher than that in milk group (P<0.01). The average daily total feed intake in milk replacer group from 41 to 60 days of age was significantly higher than that in milk group (P<0.05), but there was no significant difference between the two groups from 21 to 60 days of age (P>0.05). The diarrhea rate in milk replacer group from 41 to 60 days of age and 21 to 60 days of age was not significantly different from that in milk group (P>0.05). At 60 days of age, there were no significant differences in the contents of ammonia nitrogen and volatile fatty acids, acetic acid to propionate ratio and rumen microbial diversity indices between the two groups (P>0.05). The relative abundances of Firmicutes and Prevotella in rumen in milk replacer group was significantly higher than that in milk group (P<0.05), but there was no significant difference in the relative abundances of other bacteria between the two groups (P>0.05). The weaning survival rate in milk replacer group was 6.67 percentage points higher than that in milk group, and the weak lambing rate was 8.33 percentage points lower than that in milk group. In conclusion, compared with milk feeding, feeding milk replacer to weaned lambs at 20 days of age can reduce the growth performance and nutrient apparent digestibility and increase the diarrhea rate from 21 to 40 days of age. However, it has no significant effects on growth performance, nutrient apparent digestibility, rumen fermentation parameters, microflora structure and health status of lambs from 41 to 60 days of age, but can reduce the weak lambing rate.

Key words： lamb milk replacer; growth performance; nutrient apparent digestibility; rumen fermentation parameters; rumen microflora structure; health status

Cite this article

YANG Xunye , NIU Zhili , WU Qiong , LIU Yingming , LI Xinghua , ZHAO Zhihui , YIN Fuquan , GAO Zhenhua . Effects of Lamb Milk Replacer on Growth Performance, Apparent Nutrient Digestibility, Rumen Fermentation Parameters, Microflora Structure and Health Status of Leizhou Goats[J]. Chinese Journal of Animal Nutrition, 2023 , 35(3) : 1758 -1770 . DOI: 10.12418/CJAN2023.166

随着近年来居民饮食结构的调整,国内羊肉消费需求日益增加,这就要求肉羊生产优质高效发展,而羔羊早期断奶及羔羊成活率是制约肉羊生产的关键技术问题之一。雷州山羊是广东省粤西地区的优良地方品种、中国国家地理保护品种、广东省唯一进入《国家级畜禽遗传资源保护名录》的肉羊品种,其繁殖力强,一般胎产2~3羔^[1]。目前,雷州山羊养殖粗放,羔羊一般随母哺乳至3~4月龄断奶,这不仅会造成母羊配种周期长、繁殖性能低^[2],还会因母羊产多羔和泌乳力不足导致羔羊营养不良,患病率和死亡率上升,羔羊死亡率高达30%~50%^[3]。此外,生产实践中多羔因营养不良造成死亡多发生在出生2周后^[4]。所以羔羊代乳料的研制和应用是羔羊养殖中亟待解决的重点问题和研究热点。因此,本研究基于羔羊消化系统发育规律的研究基础^[5⇓-7],参照他人代乳料研究经验^[8⇓-10]研制出兼具营养与营养调控作用的羔羊代乳料,以期为肉羊健康高效养殖、提升养殖效益提供技术支持,并为羔羊早期断奶和代乳料研究提供试验依据。

1 材料与方法

1.1 试验材料

试验用羔羊代乳料由广东海洋大学滨海农业学院动物营养研究团队研制。试验动物为广东海洋大学雷州山羊养殖基地的雷州山羊种群中选取的体重相近、出生日龄相近的春产公羔。

1.2 试验设计

选取48只健康状况良好、体重[(1.85±0.24) kg]和出生日龄[(20±1)日龄]接近的雷州山羊公羔,以体重和出生日龄为依据进行配对设计,分为代乳料组和母乳组,每组24只,每只为1个重复。预试期10 d,正试期40 d。具体饲喂方案见试验设计(表1)。

表1 试验设计

Table 1 Experimental design

项目 Items	日龄 Days of age	代乳料组 Milk replacer group	母乳组 Milk group
预试期 Pre experiment period	10~20	母乳+开食料+代乳料训饲	母乳+开食料
正试期 Formal experiment period	21~60	代乳料+开食料	母乳+开食料

1.3 试验饲粮

羔羊代乳料由3部分组成,其中组分1占总量的98%,组分2和组分3各占总量的1%。开食料参照《肉羊饲养标准》(NY/T 816—2004)进行设计和配制。试验饲粮组成及营养水平见表2。

表2 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 (DM basis)%

项目 Items	代乳料 Milk replacer	母乳 Milk	开食料 Starter
原料 Ingredients
膨化玉米粉 Puffed corn flour	12.50
小麦粉 Wheat flour	5.00
膨化大米粉 Puffed rice flour	8.00
发酵豆粕 Fermented soybean meal (46% CP)	12.00
大豆分离蛋白 Isolated soy protein	10.00
膨化大豆 Puffed soybean	4.00
脱脂奶粉 Skim milk powder	5.30
乳清粉 Whey powder	30.00
葡萄糖 Glu	4.00
大豆磷脂油粉(膨化玉米型) Soybean lecithin oil powder (expanded corn type)	4.00
脂肪粉 Fat powder	3.00
DL-蛋氨酸盐酸盐 DL-Met hydrochloride (98.5%)	0.10
L-苏氨酸 L-Thr (98.5%)	0.05
磷酸二氢钙 Ca(H₂PO₄)₂	0.05
组分2 Component 2¹⁾	1.00
组分3 Component 3²⁾	1.00
玉米 Corn			53.0
项目 Items	代乳料 Milk replacer	母乳 Milk	开食料 Starter
豆粕 Soybean meal			33.5
小麦麸 Wheat bran			5.0
菜籽粕Rapeseed meal			5.5
石粉 Limestone			1.0
预混料 Premix³⁾			1.0
磷酸氢钙 CaHPO₄			0.5
氯化钠 NaCl			0.5
合计 Total	100.00		100.0
营养水平 Nutrient levels⁴⁾
有机物 OM	86.87	91.83	80.13
粗蛋白质 CP	22.73	23.03	17.97
粗脂肪 EE	14.44	15.24	5.87
粗灰分 Ash	7.63	0.67	10.38
粗纤维 CF	2.58		6.16
钙 Ca	1.65	1.99	1.16
磷 P	0.57	0.37	0.49

1)组分2由多矿1号(羔羊微量元素预混料)和多维1号(羔羊维生素预混料)以2:1混合制得。Component 2 was mixed with multi-mineral 1 (lamb trace element premix) and multi-vitamin 1 (lamb vitamin premix) by 2:1.

2)组分3由7%甘露果糖、5%氧化锌(50%包膜型)、5%碳酸氢钠、3%复合酶制剂(包含纤维素酶、甘露聚糖酶、蛋白酶、果胶酶等)、22%L-色氨酸、19%氯化胆碱、6%氯化钠、7%酵母粉、7%甜味剂、12%乳香香料和7%丁酸梭菌混合制得。Component 3 was mixed with 7% mannose fructose, 5% zinc oxide (50% coating type), 5% Na₂HCO₃, 3% compound enzyme preparation (including cellulase, mannanase, protease, pectinase, etc.), 22% L-Try, 19% choline chloride,6% NaCl,7% yeast powder,7% sweetener, 12% milk aroma flavor and 7% Clostridium butylicum.

3)预混料为每千克饲粮提供 The premix provided the following per kg of the diet:VA 12 000 IU,VD 2 000 IU,VE 30 IU,Cu 12 mg,Fe 64 mg,Mn 56 mg,Zn 60 mg,I 1.2 mg,Se 0.4 mg,Co 0.4 mg,Ca 3.2 g,P 1.2 g,NaCl 6.4 g。

4)有机物为干物质减去粗灰分部分,其余营养水平为实测值。OM was DM minus Ash, and the other nutrient levels were measured values.

1.4 饲养管理

代乳料组试验羔羊在出生10日龄开始分别采用奶瓶人工训饲液态代乳料,20日龄后断母乳完全饲喂代乳料;代乳料的饲喂量为体重的4%且每周调整1次,液态代乳料的浓度为1份代乳料按重量兑5份温开水,搅拌均匀后冷却至40 ℃饲喂,45日龄后逐步减量稀释饲喂,直到60日龄后完全饲喂开食料。母乳组试验羔羊为健康且接近平均体重的24只羔羊,与母羊隔栏养殖至60日龄,母羊饲喂全混合日粮。2组羔羊在7日龄给予开食料自由采食,均饲养在温度适宜、通风良好的高床圈舍,饲养管理条件均相同,自由饮水。正试期每日进食3次(09:00、15:00和21:00),正试期40 d。

1.5 测定指标及方法

1.5.1 生长性能的测定

正试期间,分别于40和60日龄晨饲前对羔羊称重,计算平均个体重(AW)和平均日增重(ADG)。记录代乳料和开食料采食量及母乳进食量,其中母乳进食量以羔羊哺乳前后体重差异记为单次母乳进食量^[11],计算平均日采食量(ADFI)和ADG。计算公式如下:

ADFI(g/d)=耗料量/试验天数;

ADG(g/d)=(末重-初重)/试验天数。

1.5.2 养分表观消化率的测定

试验各阶段结束前4 d,2组分别选择近平均体重的4只羊进行消化试验,每只羊采用本营养研究团队的专利产品(授权公布号:CN210406630U)分别单独收集粪便4 d,粪便收集混合后加入10%的盐酸和甲苯溶液固氮后烘干、称重和粉碎。母乳组另选4只母羊人工挤奶并混合后用于测定母羊奶中养分含量。常规营养成分中的干物质(DM)、粗蛋白质(CP)、粗脂肪(EE)、粗纤维(CF)、粗灰分(Ash)、钙(Ca)和磷(P)含量分别参照GB/T 6435—2014、GB/T 6432—2018、GB/T 6433—2006、GB/T 6434—2006、GB/T 6438—2007、GB/T 6436—2018和GB/T 6437—2018测定,并计算养分表观消化率,计算公式如下:

养分表观消化率(%)=[(养分摄入量-粪便排泄养分量)/养分摄入量]×100。

1.5.3 瘤胃发酵参数和菌群结构的测定

于60日龄时,对消化试验的羔羊于晨饲2 h后采用胃管式瘤胃采样器收集瘤胃液样品,4层纱布过滤后用于测定瘤胃发酵参数和菌群结构。瘤胃液中氨态氮(NH₃-N)含量采用碱性次氯酸钠-苯酚分光光度法(T/NAIA 004—2020)测定,挥发性脂肪酸含量采用气相色谱法(T/NAIA 005—2020)测定,菌群结构的测定为取过滤后瘤胃液内容物于1.5 mL冻存管干冰条件运送至测序公司测定。

1.5.4 健康状况的测定

羔羊的健康状况采用腹泻率、断奶成活率和弱羔率指标表示。腹泻率以粪便评分判定,评分≥3即认定为腹泻,粪便评分标准见表3。弱羔的判定标准为羔羊个体重低于本组平均体重的3个标准差。腹泻率、断奶成活率和弱羔率的计算公式如下:

腹泻率(%)=[(腹泻头数×腹泻天数)/(试验头数×试验天数)]×100;

断奶成活率(%)=(断奶时成活羔羊数/试验开始时羔羊数)×100;

弱羔率(%)=(断奶时弱羔数/试验开始时羔羊总数)×100。

表3 羔羊粪便评分标准

Table 3 Evaluation rules of feces of lamb

评分 Score	程度 Degree	外观 Appearance
1	正常	粗条形或者颗粒状
2	轻度	软粪便,能成形
3	中度	松软,含有大量水分的粪便
4	重度	排出四溅的液体粪便

1.6 数据处理和统计分析

试验数据采用Excel 2021进行初步整理,采用SPSS 26.0统计软件对试验数据进行配对t检验,试验数据采用平均值和均值标准误(SEM)表示,P<0.05代表差异显著,P<0.01代表差异极显著。

2 结果与分析

2.1 羔羊代乳料对羔羊生长性能的影响

由表4可知,代乳料组21日龄、60日龄羔羊AW和母乳组差异不显著(P>0.05),但40日龄AW显著低于母乳组(P<0.05)。代乳料组21~40日龄ADG显著低于母乳组(P<0.05);41~60日龄ADG高于母乳组,但差异不显著(P>0.05);21~60日龄ADG 2组间差异不显著(P>0.05)。代乳料组41~60日龄代乳料ADFI比21~40日龄提高了37.69%,而母乳组母乳平均日哺乳量却下降了30.78%。代乳料组各阶段开食料ADFI显著或极显著高于母乳组(P<0.05或P<0.01)。代乳料组21~40日龄平均日总采食量极显著低于母乳组(P<0.01),41~60日龄平均日总采食量显著高于母乳组(P<0.05),但21~60日龄2组间差异不显著(P>0.05)。

表4 羔羊代乳料对羔羊生长性能的影响

Table 4 Effects of lamb milk replacer on growth performance of lambs (n=24)

项目 Items	代乳料组 Milk replacer group	母乳组 Milk group	均值标准误 SEM	P值 P-value
平均个体重 AW/kg
21日龄 21 days of age	3.24	3.30	0.07	0.08
40日龄 40 days of age	4.31^b	4.50^a	0.70	0.04
60日龄 60 days of age	5.98	5.98	0.36	0.22
平均日增重 ADG/(g/d)
21~40日龄 21 to 40 days of age	50.94^b	56.03^a	3.66	0.04
41~60日龄 41 to 60 days of age	79.85	71.89	4.87	0.06
21~60日龄 21 to 60 days of age	65.40	63.96	2.82	0.24
代乳料平均日采食量 ADFI of milk replacer/(g/d)
21~40日龄 21 to 40 days of age	132.40
41~60日龄 41 to 60 days of age	182.30
21~60日龄 21 to 60 days of age	157.35
母乳平均日哺乳量 ADFI of milk/(g/d)
21~40日龄 21 to 40 days of age		306.83
41~60日龄 41 to 60 days of age		212.40
21~60日龄 21 to 60 days of age		259.62
开食料平均日采食量 ADFI of starter/(g/d)
21~40日龄 21 to 40 days of age	23.23^a	13.89^b	4.32	0.01
41~60日龄 41 to 60 days of age	188.17^A	128.95^B	4.17	<0.01
21~60日龄 21 to 60 days of age	105.32^A	71.40^B	4.61	<0.01
平均日总采食量 Average daily total feed intake/(g/d)
21~40日龄 21 to 40 days of age	155.63^B	297.70^A	10.70	<0.01
41~60日龄 41 to 60 days of age	370.47^a	326.41^b	11.64	0.03
21~60日龄 21 to 60 days of age	262.67	307.49	12.80	0.10

	同行数据肩标无字母表示差异不显著(P>0.05),不同小写字母表示差异显著(P<0.05),不同大写字母表示差异极显著(P<0.01)。下表同。
	In the same row, values with no letter superscripts mean no significant difference (P>0.05), while with different small letter superscripts mean significant difference (P<0.05), and with different capital letter superscripts mean extremely significant difference (P<0.01). The same as below.

2.2 羔羊代乳料对羔羊养分表观消化率的影响

由表5可知,40日龄时,代乳料组DM、CP、EE和Ash的表观消化率显著低于母乳组(P<0.05)。60日龄时,代乳料组CP表观消化率比40日龄时提高了19.15个百分点,EE表观消化率比40日龄提高了42.99个百分点,但均与母乳组差异不显著(P>0.05),其他各养分的表观消化率也均与母乳组差异不显著(P>0.05)。

表5 羔羊代乳料对羔羊养分表观消化率的影响

Table 5 Effects of lamb milk replacer on nutrient apparent digestibility of lambs (n=4)%

项目 Items	代乳料组 Milk replacer group	母乳组 Milk group	均值标准误 SEM	P值 P-value
40日龄 40 days of age
干物质 DM	65.90^b	80.76^a	4.57	0.01
粗蛋白质 CP	43.12^B	67.52^A	4.61	<0.01
粗脂肪 EE	43.79^b	77.10^a	5.61	0.01
粗纤维 CF	9.26	9.86	0.34	0.43
粗灰分 Ash	50.15^b	62.04^a	2.73	0.01
钙 Ca	53.50	51.42	3.99	0.12
磷 P	62.28	65.43	3.16	0.35
60日龄 60 days of age
干物质 DM	66.48	69.49	0.12	0.91
项目 Items	代乳料组 Milk replacer group	母乳组 Milk group	均值标准误 SEM	P值 P-value
粗蛋白质 CP	62.27	66.79	3.90	0.07
粗脂肪 EE	86.78	84.04	1.37	0.31
粗纤维 CF	28.05	26.73	1.23	0.62
粗灰分 Ash	65.17	72.70	6.96	0.32
钙 Ca	45.33	47.67	4.37	0.17
磷 P	65.17	72.70	6.96	0.32

2.3 羔羊代乳料对羔羊瘤胃发酵参数的影响

由表6可知,代乳料组瘤胃内容物NH₃-N、乙酸、丙酸、丁酸、戊酸和总挥发性脂肪酸(TVFA)含量均与母乳组差异不显著(P>0.05),乙酸/丙酸(A/P)值与母乳组差异也不显著(P>0.05)。

表6 代乳料对羔羊瘤胃发酵参数的影响

Table 6 Effects of lamb milk replacer on rumen fermentation parameters of lambs (n=4)

项目 Items	代乳料组 Milk replacer group	母乳组 Milk group	均值标准误 SEM	P值 P-value
氨态氮NH₃-N/(mg/dL)	5.66	5.48	0.20	0.69
乙酸 Acetate/(mmol/L)	56.35	54.99	6.91	0.67
丙酸 Propionate/(mmol/L)	22.34	21.21	2.67	0.87
丁酸 Acetate/(mmol/L)	24.52	25.84	5.49	1.56
戊酸 Valeric acid/(mmol/L)	2.39	2.48	0.67	1.78
总挥发性脂肪酸 TVFA/(mmol/L)	105.60	104.53	10.22	1.02
乙酸/丙酸 Acetate/propionate	2.52	2.58	0.11	0.12

2.4 羔羊代乳料对羔羊瘤胃菌群结构的影响

由表7可知,代乳料组羔羊瘤胃菌群的Chao1指数、Shannon指数和Simpson指数均大于母乳组,但差异均不显著(P>0.05)。

表7 羔羊代乳料对羔羊瘤胃菌群多样性指数的影响

Table 7 Effects of lamb milk replacer on diversity indices of rumen flora of lambs (n=4)

项目 Items	代乳料组 Milk replacer group	母乳组 Milk group	均值标准误 SEM	P值 P-value
Chao1指数 Chao1 index	1 322.80	1 124.67	13.89	0.22
Shannon指数 Shannon index	10.02	8.84	2.73	0.14
Simpson指数 Simpson index	0.992	0.991	0.000	0.09

由表8可知,在门水平上,代乳料组羔羊瘤胃菌群中的优势菌门依次为厚壁菌门、拟杆菌门和变形菌门,母乳组则依次为拟杆菌门、厚壁菌门和变形菌门;代乳料组厚壁菌门相对丰度显著高于母乳组(P<0.05),其他菌门相对丰度2组间差异不显著(P>0.05)。在属水平上,代乳料组和母乳组未鉴定菌属相对丰度分别占46.19%和54.57%,且2组间差异不显著(P>0.05);代乳料组普雷沃氏菌属相对丰度显著高于母乳组(P<0.05),曼氏杆菌属相对丰度2组间差异不显著(P>0.05)。

表8 羔羊代乳料对羔羊瘤胃菌群门、属水平相对丰度的影响

Table 8 Effects of lamb milk replacer on relative abundance of rumen flora at phylum and genus levels of lambs (n=4)%

项目 Items	代乳料组 Milk replacer group	母乳组 Milk group	均值标准误 SEM	P值 P-value
门水平相对丰度 Relative abundance at phylum level
拟杆菌门 Bacteroidetes	45.93	51.35	3.89	0.34
厚壁菌门 Firmicutes	52.45^a	37.86^b	3.07	0.04
变形菌门 Proteobacteria	1.10	1.24	0.45	0.21
螺旋体门 Spirochaetes	0.21	1.51	0.34	1.65
互养菌门 Synergistetes	0.54	0.93	0.51	0.08
属水平相对丰度 Relative abundance at genus level
未鉴定菌属 Unclassified	46.19	54.57	2.39	0.07
普雷沃氏菌属 Prevotella	43.57^a	28.85^b	3.72	0.04
曼氏杆菌属 Mannheimia	4.51	3.56	1.90	0.94

2.5 羔羊代乳料对羔羊健康状况的影响

由表9可知,代乳料组21~40日龄腹泻率极显著高于母乳组(P<0.01),41~60日龄腹泻率与母乳组差异不显著(P>0.05),21~60日龄腹泻率2组间差异不显著(P>0.05)。代乳料组断奶成活率比母乳组高6.67个百分点,弱羔率比母乳组低8.33个百分点。

表9 羔羊代乳料对羔羊健康状况的影响

Table 9 Effects of lamb milk replacer on health status of lambs (n=24)%

项目 Items	代乳料组 Milk replacer group	母乳组 Milk group	均值标准误 SEM	P值 P-value
21~40日龄腹泻率 Diarrhea rate from 21 to 40 days of age	30.00^A	11.00^B	3.87	<0.01
41~60日龄腹泻率 Diarrhea rate from 41 to 60 days of age	9.89	11.15	2.03	0.34
21~60日龄腹泻率 Diarrhea rate from 21 to 60 days of age	15.08	11.03	2.59	0.27
60日龄断奶成活率 Weaning survival rate at 60 days of age	90.00	83.33
60日龄弱羔率 Weak lamb rate at 60 days of age	16.67	25.00

3 讨论

3.1 羔羊代乳料对羔羊生长性能和养分表观消化率的影响

羔羊生长性能是评价肉羊养殖效益的主要因素之一,也是摄入养分在体内消化吸收和沉积代谢的最终体现^[12]。早期饲喂代乳料的羔羊生长性能会受到饲粮改变、饲喂方式改变和母畜分离等影响^[13]。本研究结果表明,与母乳组相比,代乳料组40日龄AW和21~40日龄ADG均显著降低,但60日龄AW和41~60日龄ADG却与母乳组无显著差异,且全期生长速度呈现前期低后期无显著差异的趋势,这与宋林等^[14]的研究结果相似。这可能是早期断母乳羔羊由于饲粮更换和母子分离造成断奶应激^[15],代乳料中植物性饲料会刺激消化道导致消化吸收功能降低所致^[16]。Wang等^[17]研究发现,大多数情况下,未经过特殊加工的植物蛋白质会给早期羔羊消化系统抵御抗营养因子带来巨大压力;但Liu等^[18]研究发现,和母乳喂养比较,改性加工后的植物蛋白质应用于代乳料中饲喂犊牛,似乎更有利于瘤胃发育。在本研究中,代乳料组41~60日龄平均日总采食量显著高于母乳组,代乳料ADFI比21~40日龄提高了37.69%,ADG超过母乳组,且60日龄时AW与母乳组相比差异不显著,这与孙进^[19]的研究结果相似。这可能是羔羊饲喂代乳料促进了消化系统尤其是瘤胃功能的完善,提高了机体对养分和环境的耐受力,机体缓解和适应后养分需求上升,代乳料组开食料ADFI显著高于母乳组也得到证实和验证^[20]。代乳料中动物蛋白质和植物蛋白质优势互补,既能够保证消化吸收,还可以激瘤胃形态的发育^[21];同时代乳料组分中的复合酶制剂以及益生菌有助于消化吸收养分和缓解消化道内环境应激^[22],促使羔羊更易适应开食料。此外,母乳组母羊后期泌乳量已经趋于下降,羔羊平均日哺乳量下降,这说明母羊后期泌乳性力及羊奶营养明显不能够满足羔羊生长,但代乳料营养全面稳定且可以按需调整饲喂量,而代乳料组液态代乳料摄入量仍增加,最终表现为代乳料组后期生长性能逐渐提高,直至与母乳组无显著差异。

饲粮中的养分含量、来源和工艺等均会影响养分表观消化率进而影响生长性能^[23]。本研究结果显示,40日龄时,代乳料组DM、CP、EE和Ash的养分表观消化率显著低于母乳组。推测是因为羔羊胃肠道发育处于过渡阶段,消化酶分泌机能尚未完善,导致酶活性和分泌量均无法满足^[24]。代乳料组60日龄养分表观消化率与母乳组无显著差异,这与杨磊等^[25]饲喂犊牛的结果一致,说明断奶应激对消化系统产生的负面影响,会随着时间的延长和动物的逐渐适应得到缓解,消化功能随着日龄增长日臻完善,对于代乳料的消化能力提高^[26]。本研究以一定比例植物蛋白质替代乳源蛋白质作为代乳料蛋白质来源,在相同蛋白质水平下,经济成本更低。植物蛋白质的消化特性是缺乏酪蛋白,在羔羊皱胃中无法像乳源蛋白质一样形成凝乳快,因此食糜由皱胃快速流向小肠。Kirchner等^[27]研究发现,这可能会导致大量未消化的养分在小肠积累,引起肠道内摩尔渗透压浓度改变,羔羊容易发生非病原性腹泻。而且蛋白质累积在肠道容易发酵产生毒素,造成肠绒毛萎缩和隐窝增生,降低小肠对养分的吸收^[28]。因此,本研究代乳料所用植物蛋白质采取发酵、膨化和分离等改性加工处理,以消除抗营养因子作用,增加蛋白质溶解特性,改性后的植物蛋白质不仅提高了消化利用效率,还能够更好地促进瘤胃发育。Porter等^[29]研究表明,植物蛋白质原料含有少量纤维成分,饲喂后瘤胃乳头发育似乎更为成熟。淀粉是动物饲粮的主要能量来源,早期断奶羔羊瘤胃发育处于过渡阶段,淀粉消化由瘤胃微生物和消化酶共同完成。淀粉的结构特性是通过分子间氢键相互作用,形成复杂稳定的螺旋或树杈结构,并形成致密的淀粉颗粒。这似乎会限制瘤胃中降解淀粉的微生物、真胃及小肠的消化酶对淀粉的降解^[30]。此外,早期羔羊瘤胃微生物和酶的数量和活性都比较低,二者均会影响淀粉的消化吸收。本代乳料所用淀粉采用糊化、膨化手段,使其淀粉分子间氢键断裂后结构松散,可以增大瘤胃微生物和消化酶的接触作用面积,还可以破坏淀粉的酶抑制因子,从而提高淀粉的消化利用率。淀粉不仅可以提供能量,还能促进瘤胃发育,Quigley等^[31]研究表明消化淀粉会产生丁酸盐和丙酸刺激瘤胃上皮发育和代谢活动。除此之外,为了有效保证早期断奶羔羊对代乳料养分的消化酶需求,本研究代乳料额外添加了外源消化酶以及益生菌^[32],以增强羔羊对代乳料中非乳成分的适应,提高饲料利用率。

3.2 羔羊代乳料对瘤胃发酵参数和瘤胃菌群结构的影响

瘤胃发酵参数是衡量瘤胃的消化功能、生理状况以及内环境稳定性的重要指标。NH₃-N反映饲粮蛋白质降解与菌体蛋白合成的动态平衡,受到饲粮养分和结构^[33]、瘤胃微生物^[34]的影响。Satter等^[35]将5.0 mg/dL作为瘤胃微生物蛋白合成效率(MPS)的NH₃-N含量的最低标准。本研究中,60日龄时,代乳料组瘤胃NH₃-N含量与母乳组相比差异不显著。挥发性脂肪酸不仅是反刍动物重要的能源物质,还是微生物增殖碳架和瘤胃发育的促进剂,受饲粮营养成分、pH以及瘤胃微生物的影响^[36-37]。乙酸和丙酸是反刍动物脂肪的主要原料,其适宜比例为2.5~3.5^[38]。本研究中,代乳料组瘤胃TVFA含量与母乳组相比差异不显著,这与韩娥等^[39]研究的成年山羊结果相似,且2组A/P值均在合理范围。这说明代乳料组60日龄羔羊瘤胃发酵功能基本完善,具备了断奶的生理基础。可能是所用代乳料原料的膨化处理破坏了植物蛋白质的纤维结构^[40],纤维素酶、有益微生物和功能性寡糖促进了瘤胃微生物的生长和活性,提高了饲料利用率^[41]。

羔羊断奶具备的先决条件是瘤胃功能向反刍阶段转变,这种变化是以瘤胃发酵能力为中心建立的,其中最关键的因素之一是瘤胃微生物区系的建立^[42]。微生物群落的丰度和多样性在统计学中常用Chao1指数、Shannon指数和Simpson指数来衡量。本研究结果表明,代乳料组瘤胃菌群的Chao1指数、Shannon指数和Simpson指数均与母乳组差异不显著,这说明与母乳喂养相比,饲喂代乳料并没有对瘤胃微生物区系的丰度和多样性造成显著差异,这表明代乳料组羔羊对于瘤胃环境变化的适应性、维稳性与母乳组无明显区别,这与Konopka^[43]的研究结果一致。造成这样结果的原因有2个:一是代乳料营养成分和母乳相近,原料种类丰富刺激瘤胃菌群发育^[44];二是开食料等固体饲料的摄入在羔羊瘤胃菌群建立中发挥着重要作用,相同的开食料摄入造就相似瘤胃内环境,演变相似丰度和多样性的菌群^[45]。Henderson等^[46]研究发现,瘤胃菌群门水平下拟杆菌门、厚壁菌门和变形菌门,属水平下普雷沃氏菌属是反刍动物核心门属微生物群,它们占据着优势且承担着主要发酵功能,具备断奶条件的山羊瘤胃菌群也应如此。Bekele等^[47]通过16S rDNA序列分析发现,山羊瘤胃普雷沃氏菌属会随着固体采食量增加成为最丰富的细菌属。本研究结果发现,60日龄时2组羔羊瘤胃核心门菌群由拟杆菌门、厚壁菌门和变形菌门组成,Abecia等^[48]研究结果也证实如此;2组菌群属水平优势菌都为普雷沃氏菌属,这与尹福泉等^[49]的研究结果一致,这表明用代乳料替代母乳饲喂羔羊,其瘤胃菌群能够和母乳组一样具备反刍发酵能力。但由于瘤胃菌群的宿主特异性,不同饲粮养分含量和来源似乎对瘤胃菌群的组成结构有着不一样的影响^[50],这可能与菌群功能特性有关^[51]。厚壁菌门能够促进宿主能量吸收,有助于饲粮纤维素的降解;拟杆菌门主要负责降解碳水化合物和蛋白质;普雷沃氏菌属对非结构性碳水化合物以及蛋白质的降解能力较强。本研究中,代乳料组和母乳组的优势菌群分别为厚壁菌门和拟杆菌门,且代乳料组厚壁菌门相对丰度更高。一方面可能是进食过程中部分液态代乳料或母乳“溢入”瘤胃成为唯一可能基质;另一方面是代乳料组分中植物蛋白质和淀粉成分的蛋白质营养和碳水化合物营养反馈性刺激厚壁菌门和普雷沃氏菌属细菌的增长,这也是代乳料组中普雷沃氏菌属相对丰度显著高于母乳组的原因。本研究还发现,尽管2组羔羊都具备断奶功能,但在属水平实际测定结果中有着大部分未鉴定菌群,这些未知菌群可能在瘤胃生态系统有着某些特殊作用,不过Ryu等^[52]研究发现未鉴定菌群在成年阶段却占据很少一部分。这说明瘤胃菌群功能的成熟早于细菌群落的成熟,这与Rey等^[53]的研究结果相似。造成上述试验结果可能和山羊品种、饲粮成分以及生长环境等因素有关,对于这部分菌群的功能和鉴定未来仍然需要继续深入去探究。

3.3 羔羊代乳料对羔羊健康状况的影响

羔羊的健康状况可以通过腹泻率和断奶成活率来反映,是羔羊消化系统发育程度以及羔羊对养分消化代谢的直接反映。在实践中,腹泻是羔羊养殖过程中的多发和常见病,引起羔羊腹泻的原因较多,其中断奶应激和代乳料成分是早期腹泻的主要非病原性原因。本研究中,代乳料组21~40日龄腹泻率显著高于母乳组,可能是羔羊对断奶应激和养分转变引起的免疫反应^[54]。李冲^[55]研究表明,湖羊羔羊因为消化机能尚未完善,由哺乳完全转为代乳料会导致肠道菌群的快速转化,可能会对肠道免疫功能造成压力。随着日龄的增长和适应代乳料,代乳料组后期腹泻率改善,41~60日龄腹泻率与母乳组相比差异不显著。可能是在代乳料中提供了益生素和益生菌,能够调整消化道微生态平衡,刺激羔羊免疫系统,增强抗病力。此外,在实践生产中尤其是肉鸡养殖中,常常通过改善群体整齐度的措施来缩小生产差距,提高整体生长性能^[56]。本研究也借鉴上述衡量指标,以体重偏离平均体重的程度作为弱羔的判定标准,既能够体现试验因素的作用结果,又可以作为群体整齐度的参考指标,由于代乳料营养全面稳定不受时间影响且可以及时调整,加之代乳料饲喂羔羊不受母体影响,能够降低患病率,因此60日龄时代乳料组弱羔率比母乳组降低了8.33个百分点,这说明代乳料组羔羊体重偏离本组平均体重的个体较少,群体整齐度较好。

4 结论

① 饲喂代乳料会降低21~40日龄羔羊生长性能和养分表观消化率,提高腹泻率。

② 饲喂代乳料对41~60日龄羔羊生长性能、养分表观消化率、瘤胃发酵参数和菌群结构及健康状况的影响与母乳组羔羊相比没有显著差异,且可以降低弱羔率。

References

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