Chinese Journal of Animal Nutrition >

2024 , Vol. 36 >Issue 6: 3713 - 3724

DOI: https://doi.org/10.12418/CJAN2024.319

RESEARCH PAPER

Effects of Dietary Crude Protein Level on Growth Performance, Nutrient Apparent Digestibility and Rumen Fermentation Parameters of Growing Water Buffalo Aged 5 to 9 Months and Its Digestible Crude Protein Requirement Prediction

  • RUAN Lijun , 1 ,
  • DENG Yingzhao 1 ,
  • YAO Yipei 1 ,
  • WEI Caixiang 1 ,
  • QIN Guangsheng 2 ,
  • WANG Ruizhanghui 1 ,
  • ZOU Caixia , 1, *
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  • 1 College of Animal Science and Technology, Guangxi University, Nanning 530003, China
  • 2 Buffalo Research Institute, Chinese Academy of Agricultural Sciences, Nanning 530001, China
*professor, E-mail:

Received date: 2023-12-14

  Online published: 2024-06-07

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Abstract

The aim of this experiment was to investigate the effects of dietary crude protein (CP) level on growth performance, nutrient apparent digestibility and rumen fermentation parameters of growing water buffalo aged 5 to 9 months, and to project the digestible crude protein (DCP) requirement of growing water buffalo. Twenty-four healthy growing water buffalo with the body weight of (210.61±6.43) kg and similar body condition were selected for the experiment. They were randomly divided into three groups: low CP level (12.72%) diet group (LP group), medium CP level (15.87%) diet group (MP group), and high CP level (19.02%) diet group (HP group), with 8 replicates per group and one buffalo per replicate. The pre-experimental period was 15 days, and the formal experimental period was 50 days. At the end of the feeding trial, each group randomly selects 5 buffalo for a 5-day digestion trial, collecting fecal and diet samples. Based on the CP content in the fecal and diet samples, the DCP intake was calculated and a prediction model for the requirement of DCP was established according to the principle of factorization. The results showed as follows: 1) the average daily gain (ADG) of growing water buffalo in the MP and HP groups was significantly higher than that of the LP group (P<0.05); the dry matter intake (DMI) of the MP and HP groups was significantly higher than that of the LP group (P<0.05). 2) The apparent digestibility of crude protein (CP) and dry matter (DM) in the MP group was significantly higher than that in the LP group (P<0.05); the apparent digestibility of ether extract (EE) in the MP and HP groups was significantly higher than that in the LP group (P<0.05); the apparent digestibility of neutral detergent fiber (NDF) in the MP group was significantly higher than that in the LP and HP groups (P<0.05). 3) The concentration of rumen fluid ammonia nitrogen (NH3-N) in the HP group was significantly higher than that in the LH and MP groups (P<0.05); the concentration of rumen fluid acetate in the LP group was significantly higher than that in the HP group (P<0.05); the concentrations of rumen fluid isobutyrate, isovalerate and valerate in the LP group were significantly higher than those in the MP and HP groups (P<0.05), and at the same time, the concentrations of rumen fluid isobutyrate, isovalerate and valerate in the MP group were significantly higher than those in the HP group (P<0.05); the butyrate/total volatile fatty acids (TVFA) ratio in the MP and HP groups was significantly higher than that in the LP group (P<0.05). 4) The maintenance DCP requirement for growing buffaloes (256 kg) was calculated as 3.51 g/(kg W0.75·d) according to the analytical factorization method, which was 266.87 g of DCP per kg of weight gain. In conclusion, feeding a diet containing 15.87% CP can improve the apparent digestibility of DM, CP, EE and NDF of growing water buffalo aged 5 to 9 months. It also can increase the concentrations of acetate, isobutyrate, isovalerate and valerate in the rumen fluid, which is beneficial for enhancing the activities of rumen microorganisms. This, in turn, it can improve the feed conversion efficiency and promote the absorption of nutrients from the diet of growing water buffalo. The prediction model for DCP requirement of growing buffalo from 5 to 9 months of age is DCP=3.51W0.75+266.87ΔW (in the model, DCP is digestible protein requirement, g/d; W0.75 is metabolic weight, kg; ΔW is daily gain, kg/d).

Key words： growing water buffalo; crude protein level; growth performance; apparent digestibility of nutrients; digestible crude protein requirement

Cite this article

RUAN Lijun , DENG Yingzhao , YAO Yipei , WEI Caixiang , QIN Guangsheng , WANG Ruizhanghui , ZOU Caixia . Effects of Dietary Crude Protein Level on Growth Performance, Nutrient Apparent Digestibility and Rumen Fermentation Parameters of Growing Water Buffalo Aged 5 to 9 Months and Its Digestible Crude Protein Requirement Prediction[J]. Chinese Journal of Animal Nutrition, 2024 , 36(6) : 3713 -3724 . DOI: 10.12418/CJAN2024.319

水牛因适应高温高湿的环境[1],且具有耐粗饲的特点而在中国南方等亚热带地区被高度驯化。由于养殖户常给水牛饲喂成本较低的粗饲料,忽视了水牛虽能充分吸收粗饲料中的养分,但也对满足其生长发育的蛋白质等养分有一定的需要量,导致生长中的水牛犊牛因缺乏营养而体重增长缓慢[2]。以科学为基础设立的饲养体系或营养标准可以有效地避免因饲粮中蛋白质过量或缺乏对反刍动物所造成的危害。前人已做过大量的试验探究出荷斯坦奶牛等反刍动物的粗蛋白质(CP)需要量,但水牛因受饲养条件的限制,只在亚热带地区分布较多,目前水牛相关营养需要的研究报道较少。
饲粮CP供应不足会导致养分的低效利用,从而降低生产力[3]。不同的CP水平会对生长水牛生长性能、养分表观消化率和瘤胃发酵参数等指标造成不同的影响,饲粮CP水平过低,则无法满足生长水牛的营养需要,饲粮CP水平过高,生长水牛无法吸收饲粮中过多养分而造成资源浪费。饲粮被反刍动物采食后,其所含的CP被瘤胃微生物经过一系列消化后最终被小肠吸收的CP称为小肠可消化粗蛋白质(IDCP)[4]。为了更贴合生产实际,我国《肉牛饲养标准》[5](NY/T 815—2004)已将IDCP作为标准,衡量动物生长所需蛋白质。若能探索出生长水牛的可消化粗蛋白质(DCP)需要量,并根据这个需要量对生长水牛进行饲喂,则可以更好地指导饲养实践,有效地降低饲养成本,减少资源浪费。
因此,本试验拟探讨不同饲粮CP水平对生长水牛生长性能、养分表观消化率和瘤胃发酵参数的影响,同时对生长水牛的DCP需要量进行预测,旨在为水牛营养标准的制定提供参考。

1 材料与方法

1.1 试验设计

饲养试验于广西上思县某水牛养殖基地完成。选取体重为(210.61±6.43) kg、5~9月龄的健康生长水牛24头,随机分为3组,即低CP水平饲粮组(LP组,CP水平为12.49%)、中CP水平饲粮组(MP组,CP水平为15.64%)、高CP水平饲粮组(HP组,CP水平为18.79%),每组8个重复,每个重复1头牛。
整个试验分为预试期和正试期,预试期为期15 d,使试验牛逐步适应所制作的试验饲粮,调整组内牛群的生理状态,使其保持在相同的水平。预试期结束后进入为期50 d的正试期,并于试验前2 d和最后2 d进行生长水牛体重的测量,用于测定生长水牛的生长性能;试验第42~46天进行为期5 d的消化试验,用于测定饲粮养分表观消化率;试验第48天进行瘤胃液的采集,用于测定瘤胃发酵参数。

1.2 试验饲粮与饲养管理

3组生长水牛均采用单栏饲喂,每日07:00、17:00进行饲喂。试验期间生长水牛采用限制性饲喂方式,自由饮水,并保证料槽里有5%的剩料量。试验饲粮为全混合日粮(TMR),其组成及营养水平见表1。
表1 试验饲粮组成及营养水平(风干基础)

Table 1 Composition and nutrient levels of experimental diets (air-dry basis)%

项目
Items		 含量 Content
LP组 LP group MP组 MP group HP组 HP group
原料 Ingredients
全株玉米青贮 Whole corn silage 62.50 50.00 37.50
啤酒糟 Brewer’s grains 12.50 25.00
玉米 Corn 22.50 22.50 22.50
豆粕 Soybean meal 11.25 11.25 11.25
食盐 NaCl 0.23 0.23 0.23
石粉 Limestone 0.75 0.75 0.75
小苏打 NaHCO3 0.49 0.49 0.49
预混料 Premix1) 2.25 2.25 2.25
诺霉克 Novasliplus 0.03 0.03 0.03
合计 Total 100.00 100.00 100.00
营养水平 Nutrient levels2)
产奶净能 NEL/(MJ/kg) 7.05 7.08 7.12
粗蛋白质 CP 12.49 15.64 18.79
粗脂肪 EE 2.48 3.00 3.52
粗灰分 Ash 7.86 7.38 7.08
有机物 OM 92.14 92.62 92.92
中性洗涤纤维 NDF 31.67 32.63 33.59
酸性洗涤纤维 ADF 18.51 17.86 17.20
钙 Ca 0.61 0.60 0.59
磷 P 0.36 0.37 0.39

1)每千克预混料含有 One kg of premix contained the following:NaCl 151.2 g,Ca 141.7 g,P 21.6 g,VA 261 000 IU,VD3 60 000 IU,VE 1 545 IU,Cu 0.58 g,Zn 2.19 g,Mn 2.19 g。

2)产奶净能为参考《中国饲料成分及营养价值表(2022年第33版)》[6]所得计算值,其余为实测值。NEL was a calculated value obtained by reference to Tables of Feed Composition and Nutritive Values in China (2022 thirty-third edition)[6], while the others were measured values.

1.3 测定指标与方法

1.3.1 常规营养成分的测定

每周采集生长水牛饲粮及剩料500 g风干保存,所有风干样品混合后粉碎过40目筛用于营养成分测定。其中,干物质(DM)含量参考GB/T 6435—2014测定,CP含量参考GB/T 6432—2018采用Vap50s Gerhardt全自动凯氏定氮仪测定,粗脂肪(EE)含量参考GB/T 6433—2006采用索氏提取法测定,粗灰分(Ash)含量参照GB/T 6438—2007进行测定,然后用DM含量减去Ash含量得到有机物(OM)含量,钙(Ca)含量参照GB/T 6436—2018进行测定,磷(P)含量参考GB/T 6437—2018进行测定,中性洗涤纤维(NDF)和酸性洗涤纤维(ADF)含量参照Van Soest等[7]的方法进行测定。

1.3.2 生长性能的测定

试验期间记录每头生长水牛每日的采食量,试验结束后用于计算每组生长水牛的平均日采食量和干物质采食量(DMI)。在正式试验开始前2 d和最后2 d晨饲前进行连续2 d的称重,目的是减少因生长水牛排泄粪便所造成的误差,用以计算整个试验期间每组生长水牛的平均日增重(ADG);根据DMI和ADG计算料重比(F/G)。

1.3.3 养分表观消化率的测定

试验第42~46天采用内源指示剂法进行为期5 d的消化试验。在消化试验期间,每天采集2次粪便(12:00、20:00),从生长水牛的直肠中取粪,每次取鲜粪200 g并加入10%稀硫酸用以固氮,鲜粪与稀硫酸的比例为1∶10,将固好氮的鲜粪放入-20 ℃冰箱中保存,共收集5 d,待消化试验结束后将每头牛5 d的粪便分别混合均匀并从中取500 g置于65 ℃烘箱中烘至恒重,粉碎过40目筛后干燥保存。参照1.3.1中方法测定粪便中常规营养成分含量,并参照GB/T 23742—2009测定饲粮和粪便中盐酸不溶灰分含量,计算养分表观消化率。

饲粮DM表观消化率(%)=100×[1-(饲粮中盐酸不溶灰分含量/粪便中盐酸不溶灰分含量)];

饲粮某养分表观消化率(%)=100×[1-(饲粮中盐酸不溶灰分含量/粪便中盐酸不溶灰分含量)×(粪便中该养分含量/饲粮中该养分含量)]。

1.3.4 瘤胃发酵参数的测定

在正式试验最后1天晨饲前,采取口腔采取瘤胃液的方法[8]采集水牛的瘤胃液,具体方法为:将水牛的头部固定,用手抓住鼻中隔并抬起,然后将口腔胃管从门牙和臼齿之间的无牙部分插入口腔,口腔胃管通过动物吞咽通过食道缓慢推入瘤胃。弃掉采集初始时的瘤胃液,约为50 mL,另抽取200 mL瘤胃液,用干净的塑料瓶收集,经过4层纱布过滤后立即用便携式pH计(雷磁PHS-25,上海仪电科学仪器股份有限公司)测定pH,随后将其分装到10 mL的冻存管中,并放置于液氮中暂存,之后-80 ℃保存用于瘤胃发酵参数的测定。其中,氨态氮浓度参照冯宗慈等[9]改进的比色法进行测定,乳酸浓度参考杨平平等[10]的对羟基联苯法进行测定,挥发性脂肪酸浓度参照Yeo等[11]的方法进行测定。

1.3.5 CP采食量(CPI)和DCP采食量(DCPI)的计算

CPI(g/d)=DMI×饲粮中CP含量;

每千克代谢体重CPI[g/(kg W0.75·d)]=DMI×饲粮中CP含量/代谢体重;

DCPI(g/d)=CPI×CP表观消化率;

每千克代谢体重DCPI[g/(kg W0.75·d)]=CPI×CP表观消化率/代谢体重。

1.4 数据统计与分析

所有试验数据用Excel 2021进行初步整理,采用SPSS 20.0进行单因素方差分析(one-way ANOVA),差异显著时采用LSD法进行多重比较,P<0.05表示差异显著,P>0.05表示差异不显著。数据采用平均值和均值标准误(SEM)表示。

2 结果与分析

2.1 饲粮CP水平对生长水牛生长性能的影响

由表2可知,各组生长水牛的初重(IBW)、末重(FBW)和F/G没有显著差异(P>0.05);在ADG方面,HP组和MP组生长水牛的ADG显著高于LP组(P<0.05),HP组和MP组之间无显著差异(P>0.05);在DMI方面,MP组和HP组生长水牛的DMI显著高于LP组(P<0.05),HP组和MP组之间无显著差异(P>0.05)。
表2 饲粮CP水平对生长水牛生长性能的影响

Table 2 Effects of dietary CP level on growth performance of growing water buffalo

项目
Items		 LP组
LP group		 MP组
MP group		 HP组
HP group		 SEM P值
P-value
初重 IBW/kg 208.84 207.25 215.75 6.43 0.860
末重 FBW/kg 246.44 254.09 263.22 7.02 0.641
平均日增重 ADG/(kg/d) 0.75b 0.94a 0.95a 0.03 0.023
干物质采食量 DMI/(kg/d) 3.78b 4.60a 4.75a 0.13 0.001
料重比 F/G 5.09 5.05 5.03 0.15 0.988

同行数据肩标不同小写字母表示差异显著(P<0.05),相同小写字母或无字母表示差异不显著(P>0.05)。下表同。

In the same row, values with different small letter superscripts mean significant difference (P<0.05), while with the same small letter or no letter superscripts mean no significant difference (P>0.05). The same as below.

2.2 饲粮CP水平对生长水牛养分表观消化率的影响

由表3可知,各组生长水牛的ADF和OM表观消化率无显著差异(P>0.05);MP组生长水牛的CP和DM表观消化率显著高于LP组(P<0.05),但与HP组无显著差异(P>0.05);MP组和HP组生长水牛的EE表观消化率显著高于LP组(P<0.05),MP组和HP组之间无显著差异(P>0.05);MP组生长水牛的NDF表观消化率显著高于LP组和HP组(P<0.05)。
表3 饲粮CP水平对生长水牛养分表观消化率的影响

Table 3 Effects of dietary CP level on nutrient apparent digestibility of growing water buffalo%

项目
Items		 LP组
LP group		 MP组
MP group		 HP组
HP group		 SEM P值
P-value
干物质 DM 67.88b 70.15a 69.16ab 0.33 0.008
粗蛋白质 CP 72.52b 74.88a 73.41ab 0.35 0.008
中性洗涤纤维 NDF 66.29b 69.49a 66.59b 0.52 0.008
酸性洗涤纤维 ADF 60.82 62.97 61.54 0.46 0.146
粗脂肪 EE 71.53b 77.77a 76.95a 1.12 0.014
有机物 OM 54.80 57.16 55.85 0.76 0.477

2.3 饲粮CP水平对生长水牛瘤胃发酵参数的影响

由表4可知,各组生长水牛的瘤胃液pH以及乳酸、乙酸、丁酸、总挥发性脂肪酸浓度与丁酸/总挥发性脂肪酸比值均无显著差异(P>0.05);HP组和MP组生长水牛的瘤胃液NH3-N、丙酸、异戊酸、戊酸浓度与丙酸/总挥发性脂肪酸比值均显著高于LP组(P<0.05),HP组和MP组之间无显著差异(P>0.05);MP组生长水牛的瘤胃液异丁酸浓度显著高于HP组和LP组(P<0.05),同时HP组显著高于LP组(P<0.05);LP组的乙酸/丙酸和乙酸/总挥发性脂肪酸比值显著高于MP组和HP组(P<0.05),MP组和HP组之间无显著差异(P>0.05)。
表4 饲粮CP水平对生长水牛瘤胃发酵参数的影响

Table 4 Effects of dietary CP level on rumen fermentation parameters of growing water buffalo

项目
Items		 LP组
LP group		 MP组
MP group		 HP组
HP group		 SEM P值
P-value
pH 7.22 7.21 7.19 0.02 0.786
氨态氮 NH3-N(mg/dL) 7.13b 10.15a 11.83a 0.59 <0.001
乳酸 Lactic acid/(mmol/L) 0.24 0.27 0.28 0.01 0.121
总挥发性脂肪酸 TVFA(mmol/L) 57.00 60.99 59.50 0.77 0.099
乙酸 Acetate/(mmol/L) 41.95 43.20 42.03 0.63 0.707
丙酸 Propionate/(mmol/L) 9.50b 11.80a 11.50a 0.27 <0.001
丁酸 Butyrate/(mmol/L) 4.15 4.27 4.31 0.05 0.429
异丁酸 Isobutyrate/(mmol/L) 0.54c 0.67a 0.63b 0.01 <0.001
异戊酸 Isovalerate/(mmol/L) 0.55b 0.65a 0.63a 0.01 <0.001
戊酸 Valerate/(mmol/L) 0.31b 0.40a 0.40a 0.01 <0.001
乙酸/丙酸 Acetate/propionate 4.42a 3.66b 3.66b 0.11 <0.001
乙酸/总挥发性脂肪酸 Acetate/TVFA 0.74a 0.71b 0.71b 0.01 <0.001
丙酸/总挥发性脂肪酸 Propionate/TVFA 0.17b 0.19a 0.19a 0.00 <0.001
丁酸/总挥发性脂肪酸 Butyrate/TVFA 0.07 0.07 0.07 0.00 0.571

2.4 饲粮CP水平对生长水牛CPI和DCPI的影响

由表5可知,3组生长水牛的CPI和DCPI彼此间均具有显著差异(P<0.05),其中HP组显著高于LP组和MP组(P<0.05);生长水牛的每千克代谢体重CPI和每千克代谢体重DCPI则表现为MP组和HP组显著高于LP组(P<0.05),MP组和HP组之间无显著差异(P<0.05)。
表5 饲粮CP水平对生长水牛CPI和DCPI的影响

Table 5 Effects of dietary CP level on CPI and DCPI of growing water buffalo

项目
Items		 LP组
LP group		 MP组
MP group		 HP组
HP group		 SEM P值
P-value
粗蛋白质采食量 CPI/(g/d) 512.47c 691.97b 825.05a 41.20 <0.001
每千克代谢体重粗蛋白质采食量
CPI per kg of W0.75/[g/(kg W0.75·d)]		 8.32b 11.12a 12.30a 0.58 0.002
可消化粗蛋白质采食量 DCPI/(g/d) 370.98c 516.04b 607.05a 38.65 <0.001
每千克代谢体重可消化粗蛋白质采食量
DCPI per kg of W0.75/[g/(kg W0.75·d)]		 6.02b 8.28a 9.05a 0.44 0.001

2.5 生长水牛DCP需要量模型的建立

将本试验所得的饲粮DCPI(g/d)与日增重(ΔW,kg/d)的实测值进行线性回归,得到关于ΔW的DCPI预测方程:

DCPI=266.87ΔW+224.54,

(R2=0.444 5,n=15)

当ΔW=0时,DCPI=224.54,即生长水牛ADG为零时维持需要DCP为224.54 g/d,试验中3组生长水牛的平均体重为256.31 kg,换算出DCP需要量为3.51 g/(kg W0.75·d),试验牛每增重1 kg需要DCP 266.87 g/d。根据析因法原理,建立DCP需要量的预测模型为:

DCP=3.51W0.75+266.87ΔW

式中:DCP为DCP需要量(g/d);W0.75为代谢体重(kg);ΔW 为日增重(kg/d)。

3 讨论

3.1 饲粮CP水平对生长水牛生长性能的影响

动物通过将饲粮所含的能量和蛋白质转化为自身所需的养分从而满足其维持和生产的需要。如果能够寻找到满足动物维持和生产需要的最适饲粮CP水平范围,将会在生产上带来较大的收益。Blome等[12]通过设置4个CP水平(16.1%、18.5%、22.9%和25.8%)梯度饲粮探求饲粮不同CP水平对犊牛生长性能的影响,结果发现,随着饲粮CP水平的升高,犊牛的ADG也随之升高。Brosh等[13]对犊牛的蛋白质需要量进行了研究,发现饲喂高CP水平饲粮的犊牛ADG显著高于饲喂低CP水平饲粮的犊牛。李红丽等[14]分别给育肥牦牛饲喂低、中和高CP水平饲粮,结果显示中、高CP水平饲粮组的ADG显著高于低CP水平饲粮组。王强[15]给3~5月龄湖羊羔羊饲喂CP水平分别为12.8%和15.3%的饲粮,发现给湖羊羔羊饲喂高CP水平饲粮后其ADG上升,与王雁灿[16]和黄文琴等[17]的试验结果相似。Broderick等[18]、Barros等[19]和Reynal等[20]研究发现,泌乳奶牛采食高CP水平饲粮时,其DMI相对于采食低CP水平饲粮时显著升高。Broderick[21]研究发现,与饲喂15.1 g/kg CP饲粮相比,饲喂167 g/kg CP饲粮和184 g/kg CP饲粮的泌乳奶牛DMI分别增加0.9和1.4 kg/d。此外,马铁伟等[22]研究发现,湖羊采食高CP水平(15.33%)饲粮后降低了F/G。本研究同样发现,ADG和DMI随着饲粮CP水平的升高而升高,MP组和HP组的ADG和DMI均显著高于LP组。这可能是因为生长水牛处于生长发育阶段,对蛋白质的需要量较高,致使其DMI和ADG上升,同时MP组与HP组饲粮中添加了啤酒糟,而啤酒糟具有特殊的香味,可以促进生长水牛采食量的增加;此外,还可能是因为MP组生长水牛瘤胃液中异丁酸、异戊酸和戊酸浓度较高,提高了生长水牛对饲粮纤维的转化率,从而增加了饲料转化效率,表现为ADG增加。

3.2 饲粮CP水平对生长水牛养分表观消化率的影响

动物对饲粮中养分的利用状态可以用养分表观消化率来表示。Chanthakhoun等[23]通过研究饲粮不同CP水平(92、124、181和219 g/kg)对沼泽型水牛养分表观消化率的影响,发现在124、181和219 g/kg CP水平下,DM和CP的表观消化率显著提高;在124和181 g/kg CP水平下,OM和NDF的表观消化率显著提高;ADF的表观消化率在各CP水平间差异不显著。Gabler等[24]给犊牛饲喂高精料饲粮,随着饲粮CP水平的增加,DM表观消化率增加。Tauqir等[2]设置3个CP水平(11.85%、14.22%和16.50%)梯度饲粮饲喂6月龄的水牛犊牛,发现16.50%CP组的DM和NDF表观消化率显著高于11.85% CP组和14.22% CP组,14.22% CP组的DM表观消化率显著高于11.85% CP组,各组之间CP表观消化率无显著差异,但随着饲粮CP水平的升高,CP表观消化率随之上升。Panadi等[25]研究显示,随着饲粮CP水平的升高,杜泊羔羊的CP和EE表观消化率升高。周汉林等[26]、Ghorbani等[27]和王春昕等[28]的报道具有相似结果。本试验中,MP组和HP组的CP含量高于LP组,MP组和HP组的DM、CP、NDF和EE表观消化率均高于LP组,这与上述研究结果一致,可能是因为高饲粮CP水平满足了生长水牛对蛋白质的需要量,提高了瘤胃中微生物活性,从而提高了生长水牛对饲粮养分的吸收与利用,因此,在高饲粮CP水平下,生长水牛对各营养成分的消化吸收较好。除此之外,本试验结果还显示,与MP组相比,HP组DM、CP、NDF、ADF、EE和OM的表观消化率均有所降低,这可能是因为MP组饲粮CP水平达到了生长水牛可消化利用的最适饲粮CP水平范围,在此基础上再增加饲粮CP水平则会使得生长水牛因无法吸收过多的养分而造成各养分表观消化率的下降;与此同时,HP组除EE表观消化率外的各养分表观消化率虽与LP组相比无显著差异但在数值上均高于LP组,这可能与饲粮CP水平升高促进了生长水牛采食和增加了瘤胃可降解CP水平以及提高了瘤胃降解率等有关。

3.3 饲粮CP水平对生长水牛瘤胃发酵参数的影响

挥发性脂肪酸的生成速率和程度受碳水化合物组分和碳水化合物的可降解性影响。Zou等[7]报道,水牛瘤胃液的pH在7.05~7.55变动,本试验所测各组生长水牛瘤胃液的pH均在此区间范围内。牛骁麟等[29]和王春梅等[30]在湖羊上以及Zhu等[31]和甄虎等[32]在生长牦牛上进行的研究均发现,试验动物采食高CP水平的饲粮时,其瘤胃液NH3-N浓度显著上升。郭庆河等[33]在泌乳早期奶牛上也得出相似的结论。本试验结果与以上研究结论一致,可能是因为饲粮CP水平升高,使得生长水牛食入的饲粮氮上升。甄虎等[32]研究发现,中CP水平饲粮组的瘤胃液丙酸浓度显著低于高CP水平饲粮组。王波[34]研究发现,随着饲粮CP水平的降低,60日龄湖羊羔羊的瘤胃液pH和乙酸浓度上升。Chanthakhoun等[23]研究发现,沼泽型水牛瘤胃液pH在高CP水平下较低,瘤胃液NH3-N浓度随饲粮CP水平的升高而增加;此外,在181和219 g/kg CP水平下,丙酸浓度显著增加。王荣蛟[35]研究指出,随着饲粮CP水平的上升,奶水牛瘤胃液异丁酸、异戊酸和戊酸浓度均显著上升,且乙酸/丙酸值显著下降。甄虎等[32]的研究也得出相似的结论。本试验结果显示,HP组和MP组生长水牛的瘤胃液NH3-N、丙酸、异戊酸、戊酸浓度与丙酸/总挥发性脂肪酸比值均显著高于LP组;MP组瘤胃液异丁酸浓度显著高于HP组和LP组,HP组瘤胃液异丁酸浓度显著高于LP组。这可能是因为,随着饲粮CP水平的上升,生长水牛摄入的蛋白质也随之上升,从而提高了生长水牛对饲粮养分的消化吸收,提高了瘤胃微生物活性,加剧了瘤胃微生物对饲粮蛋白质的降解[36],导致瘤胃液中NH3-N、丙酸、异戊酸和戊酸浓度升高,提高了瘤胃纤维分解菌的活性,使生长水牛充分的将粗饲料中难以降解的纤维降解为可以吸收的养分。此外,本试验还发现LP组生长水牛的瘤胃液乙酸/丙酸和乙酸/总挥发性脂肪酸比值显著高于MP组和HP组。这可能是因为LP组饲粮的CP水平较低,瘤胃发酵类型为乙酸型发酵,也可能是因为随着饲粮CP水平的升高,瘤胃液中异丁酸、异戊酸和戊酸浓度升高,导致丙酸浓度随之升高,瘤胃发酵类型转化为丙酸型发酵,从而使得LP组瘤胃液中乙酸/丙酸值显著高于MP组和HP组。Wang等[37-38]、Liu等[39-40]的研究均得出与本试验相似的结论。但本试验结果与张振威等[41]的结论不同,可能是因为所选试验动物、饲养环境、饲料原料种类及采样手法上存在差异,具体原因还有待进一步的深究。王其炎[42]给水牛犊牛饲喂16.42%CP水平的饲粮,发现其乙酸/总挥发性脂肪酸比值为71%,丙酸/总挥发性脂肪酸比值为18%。张勤[43]给水牛饲喂13.79%CP水平的饲粮,得出乙酸/总挥发性脂肪酸比值为75%,丙酸/总挥发性脂肪酸比值为15.4%。以上结果均与本试验结果相似。

3.4 生长水牛DCP需要量

反刍动物的DCP需要量受品种、生长阶段、体重、身体健康状况和饲养环境等影响。高艳霞等[44]研究得出,300 kg左右的中国荷斯坦奶牛DCP需要量为3.9 g/(kg W0.75·d),每千克增重所需DCP为418.04 g。张晓明等[45]研究得出,290 kg左右的秦川公牛DCP需要量为3.71 g/(kg W0.75·d),每千克增重所需DCP为285.22 g。刘道杨等[46]研究得出,270 kg左右的湘中黑牛DCP需要量为2.66 g/(kg W0.75·d),每千克增重所需DCP为377.95 g。张莹等[3]研究得出,380 kg左右的华西牛DCP需要量为4.36 g/(kg W0.75·d),每千克增重所需DCP为127.10 g。刘道杨等[47]研究得出,275 kg左右的夏南牛DCP需要量为2.79 g/(kg W0.75·d),每千克增重所需DCP为260.69 g。穆阿丽等[48]研究得出,183 kg左右的利木赞×鲁西黄牛杂交生长牛DCP需要量为4.91 g/(kg W0.75·d),每千克增重所需DCP为351.87 g。赵峰[49]研究得出,220 kg左右的后备母水牛DCP需要量为2.2 g/(kg W0.75·d),每千克增重所需的DCP为368.39 g。本研究得出,256 kg左右的生长水牛DCP需要量为3.51 g/(kg W0.75·d),略高于刘道杨等[46]对湘中黑牛[2.66 g/(kg W0.75·d)]、刘道杨等[47]对夏南牛[2.79 g/(kg W0.75·d)]、赵峰[49]对后备母水牛[2.20 g/(kg W0.75·d)]和陈福音等[50]对荷斯坦奶牛[3.37 g/(kg W0.75·d)]的研究结果,可能是因为本试验所选牛的品种和生长阶段与前人不同所致。本试验所得生长水牛每千克增重所需的DCP为266.87 g,低于高艳霞等[44]对中国荷斯坦奶牛、张晓明等[45]对秦川公牛、刘道杨等[44]对湘中黑牛和穆阿丽等[48]对利木赞×鲁西黄牛杂交生长牛的研究结果,说明生长水牛对蛋白质的吸收利用率高。通过表6可知,本试验所得DCP预测模型的决定系数(R2)偏低,可能是因为本试验是在广西某公司的养殖场内进行,该养殖场不具备完善的试验条件,在给生长水牛称重时造成一定的误差;也可能是因为本试验所用的是生长反应法去预测生长水牛的DCP需要量,通过此法预测出的DCP需要量具有一定的误差;还可能是因为本试验选取的试验牛头数较少造成了一定的误差;此外,本试验在进行生长水牛DCP需要量的预测时考虑了个体差异,这也可能是造成R2偏低的原因。因此,今后还有待进一步的试验去补充生长水牛的DCP需要量。
表6 不同品种牛DCP需要量预测模型

Table 6 Predictive models for DCP requirement of different breeds of cattle

品种
Breeds		 体重
BW/kg		 维持需要DCP
Maintenance requirement
of DCP/[g/
(kg W0.75·d)]		 预测模型
Predictive
model		 样本数
n		 决定系数
R2		 参考文献
Reference
荷斯坦奶牛
Holstein cows		 182.81±2.62 3.37 DCP=3.37W0.75+394.29ΔW 21 0.984 [50]
中国荷斯坦奶牛
China Holstein
cows		 307.67±2.99 3.9 DCP=3.90W0.75+418.04ΔW 21 [44]
秦川公牛
Qinchuan bulls		 289.33±17.79 3.71 DCP=3.71W0.75+285.22ΔW 30 0.942 [45]
湘中黑牛
Xiangzhong
black cattle		 273.77±15.97 2.66 DCP=2.66W0.75+377.95ΔW 15 0.994 [46]
华西牛
Huaxi cattle		 379.30±39.46 4.36 DCP=4.36W0.75+127.10ΔW 30 0.989 [3]
夏南牛
Xianan cattle		 275.57±8.99 2.79 DCP=2.79W0.75+260.69ΔW 30 0.998 [47]
利木赞×鲁西黄
牛杂交生长牛
Limousin×Luxi
cross-bred
beef cattle		 183.58±7.89 4.91 DCP=4.91W0.75+351.87ΔW 18 [48]
后备母水牛
Heifer dairy buffalo		 220.50±27.32 2.2 DCP)=2.20W0.75+368.39ΔW 12 [49]
生长水牛
Growing buffalo		 256.31±29.80 3.51 DCP=3.51W0.75+266.87ΔW 15 0.444 本试验

DCP:DCP需要量(g/d);W0.75:代谢体重(kg);ΔW:日增重(kg/d)。

DCP: DCP requirement (g/d); W0.75: metabolic body weight (kg); ΔW: daily gain (kg/d).

4 结论

① 饲喂15.87% CP水平饲粮的生长水牛具有较高的ADG和DMI,F/G下降,减少了饲养成本,提高了经济效益。
② 饲喂15.87% CP水平饲粮的生长水牛的DM、CP、NDF和EE表观消化率最高,且与饲喂12.72%和19.02% CP水平饲粮的生长水牛相比具有显著差异,同时瘤胃液中乙酸/丙酸比值下降,表明饲喂15.87% CP水平饲粮的生长水牛对饲粮中养分的消化吸收最好。
③ 体重在256 kg左右的生长水牛的DCP为3.51 g/(kg W0.75·d),每千克增重所需的DCP为266.87 g,得出生长水牛的DCP需要量预测模型为:DCP=3.51W0.75+266.87ΔW(DCP为DCP需要量,g/d;W0.75为代谢体重,kg;ΔW为日增重,kg/d)。
④ 综上所述,饲喂15.87% CP水平的饲粮能够更好地促进5~9月龄生长水牛对饲粮营养成分的消化吸收和利用。

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