Chinese Journal of Animal Nutrition >

2023 , Vol. 35 >Issue 1: 323 - 334

DOI: https://doi.org/10.3969/j.issn.1006-267x.2023.01.033

RESEARCH PAPER

Effects of Supplementation of Betaine, Vitamins and Electrolyte Ions Compound Additive in Summer on Performance, Energy Balance and Serum Biochemical Indexes of Dairy Cows during Peripartum Period and Early Lactation Period

  • FENG Linyu , 1 ,
  • ZHANG Xiongfei 1 ,
  • LIU Zhuangzhuang 2 ,
  • ZHANG Tianshu 3 ,
  • WANG Qilin 1 ,
  • DENG Lu 1 ,
  • CAO Yangchun 1 ,
  • YAO Junhu 1 ,
  • LEI Xinjian , 1, *
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  • 1 College of Animal Science and Technology, Northwest A&F University, Yangling 712100, China
  • 2 College of Veterinary Medicine, Northwest A&F University, Yangling 712100, China
  • 3 Liaoning Inspection, Examination & Certification Centre (Liaoning Institute for Agro-Product Veterinary Drugs and Feed Control), Shenyang 110000, China
* associate professor, E-mail:

Received date: 2022-06-29

  Online published: 2023-01-11

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Abstract

The objective of this study was to investigate the effects of supplementation of betaine, vitamins and electrolyte ions compound additive in summer on performance, energy balance and serum biochemical indexes of dairy cows during peripartum period and early lactation period. Thirty healthy Holstein dairy cows with similar parity [(2.3±0.8) parities], milk yield in last lactation period [(28.3±1.6) kg/d] and expected calving date [(25.6±3.5) d] were randomly divided into 2 groups in randomized block design with 15 replicates per group and 1 cow per replicate. Cows in the control group (CON group) were fed a basal diet during whole experiment period (day 21 before delivery to day 63 after delivery); while cows in compound additive group (CA group) were fed the basal diet supplemented with 40 g/d betaine, vitamins and electrolyte ions compound additive during peripartum period (day 21 before delivery to day 21 after delivery), and supplemented with 10 g/d betaine, vitamins and electrolyte ions compound additive during early lactation period (days 22 to 63 after delivery). The experiment lasted for 84 days. The results showed as follows: 1) the respiratory rate of cows during peripartum period and whole experiment period of CA group was significantly lower than that of CON group (P<0.05). 2) During the peripartum period, the dry matter intake (DMI) of cows of CA group was significantly higher than that of CON group (P<0.05); during the early lactation period, the DMI and milk yield of cows of CA group were significantly higher than that of CON group (P<0.05); during the whole experiment period, the DMI and 4% fat-corrected milk yield of cows of CA group were significantly higher than that of CON group (P<0.05). 3) The serum nonestesterified fatty acid content on day 14 before delivery and day 63 after delivery of CA group was significantly lower than that of CON group (P<0.05). The serum aspartate aminotransferase activity on day 14 before delivery of CA group was significantly lower than that of CON group (P<0.05), the serum albumin content on day 21 after delivery was significantly higher than that of CON group (P<0.05), and the serum total bilirubin content on day 63 after delivery was significantly lower than that of CON group (P<0.05). The serum catalase activity on day 14 before delivery of CA group was significantly higher than that of CON group (P<0.05). In conclusion, the supplementation of betaine, vitamins and electrolyte ions compound additive in summer can alleviate the heat stress and negative energy balance, improve the performance of dairy cows during the peripartum period and early lactation period, and improve the immune function and antioxidant capacity of dairy cows during the peripartum period.

Key words： compound additive; dairy cows; peripartum period; early lactation period; performance; heat stress

Cite this article

FENG Linyu , ZHANG Xiongfei , LIU Zhuangzhuang , ZHANG Tianshu , WANG Qilin , DENG Lu , CAO Yangchun , YAO Junhu , LEI Xinjian . Effects of Supplementation of Betaine, Vitamins and Electrolyte Ions Compound Additive in Summer on Performance, Energy Balance and Serum Biochemical Indexes of Dairy Cows during Peripartum Period and Early Lactation Period[J]. Chinese Journal of Animal Nutrition, 2023 , 35(1) : 323 -334 . DOI: 10.3969/j.issn.1006-267x.2023.01.033

围产期是决定奶牛泌乳阶段生产效率和健康状况的关键时期。产前胎儿快速增长挤压瘤胃、产前和产后饲粮营养结构变化、胎儿分娩以及泌乳启动等生理、营养和代谢方面的变化,导致干物质采食量(dry matter intake,DMI)下降[1]。但胎儿发育、自身维持和泌乳都需要大量营养物质和能量。泌乳启动后,由于产后DMI恢复滞后于产奶量的增加,营养摄入远不能满足泌乳及机体恢复需要[2]。因此,围产期和泌乳前期奶牛往往处于能量负平衡(negative energy balance,NEB)状态。此时机体通过体脂动员满足能量需要,脂质代谢增强,自由基积累增加,免疫功能下降,导致围产期奶牛易发生代谢性疾病,威胁奶牛健康,降低生产性能[3]。奶牛汗腺不发达,难以通过自身调节适应夏季的高温环境,易发生热应激,对生产性能、抗氧化能力、免疫功能等产生不利影响[4]。缓解夏季围产期和泌乳前期NEB和热应激对改善奶牛机体健康和生产性能具有重要意义。
甜菜碱可作为甲基供体,促进脂肪酸的β-氧化[5]。因偶极离子的化学结构特性,甜菜碱具有渗透压调节作用。此外甜菜碱具有分子伴侣的功能,可通过增强折叠状态蛋白质氢键,维持细胞正常形态与功能,缓解热应激[6]。研究表明,饲粮补饲甜菜碱可缓解围产期和泌乳期奶牛热应激,提高生产性能[7]。维生素是动物的必需营养素,对缓解奶牛NEB和热应激有重要作用。维生素A可在转录水平调控抗氧化反应相关基因,发挥抗氧化功能[8]。维生素B6作为辅酶参与糖异生过程,是调节细胞生化反应的关键因子[9]。研究表明,产前补饲维生素C可提高奶牛抗氧化能力,缓解肝脏损伤[10]。维生素D3可调节免疫功能,改善围产期奶牛健康状况[11]。维生素E作为活性氧清除剂可保护细胞膜脂质过氧化[12]。镁离子(Mg2+)可通过提高抗氧化酶活性缓解氧化应激[13]。热应激奶牛补充电解质离子可预防因大量出汗时钠离子(Na+)、钾离子(K+)等电解质离子流失引发的电解质紊乱[14]。单一补饲甜菜碱、维生素及电解质离子调控奶牛NEB和热应激的研究较多,但其组合效果鲜有报道。因此,本试验旨在研究补饲甜菜碱、维生素及电解质离子复合添加剂对夏季围产期和泌乳前期奶牛生产性能和机体健康的影响,以期为通过营养调控缓解夏季围产期和泌乳前期奶牛NEB和热应激提供科学依据。

1 材料与方法

1.1 试验材料

本试验采用的甜菜碱、维生素及电解质离子复合添加剂由新加坡某饲料添加剂公司提供,其主要成分和含量如表1所示。
表1 甜菜碱、维生素及电解质离子复合添加剂主要成分和含量

Table 1 Main components and contents of betaine, vitamins and electrolyte ions compound additive

项目
Items		 含量
Content
维生素A Vitamin A/(IU/kg) 3 000 000~6 000 000
维生素D3 Vitamin D3/(IU/kg) 500 000~1 000 000
维生素E Vitamin E/(IU/kg) ≥1 000
维生素B6 Vitamin B6/(mg/kg) ≥400
维生素C Vitamin C/(mg/kg) ≥7 000
维生素K3 Vitamin K3/(mg/kg) ≥1 650
甜菜碱Betaine/(mg/kg) ≥200 000
氯化钠NaCl/(mg/kg) 80 000~250 000
氯化钾KCl/(mg/kg) ≥25 000
氯化镁MgCl2/(mg/kg) 13 000~26 000

1.2 试验设计

选取30头胎次[(2.3±0.8)胎]、上一泌乳周期产奶量[(28.3±1.6) kg/d]、预产期[(25.6±3.5) d]相近的健康荷斯坦奶牛,按照完全随机区组设计分为2组,每组15个重复,每个重复1头牛。试验于2021年6月至2021年9月在陕西省宝鸡市某规模化奶牛场进行。试验期为产前21 d至产后63 d,共84 d。对照组(CON组)试验全期(产前第21天至产后第63天)饲喂基础饲粮;添加剂组(CA组)在围产期(产前第21天至产后第21天)每头牛补饲40 g/d甜菜碱、维生素及电解质离子复合添加剂,在泌乳前期(产后第22~63天)每头牛补饲10 g/d甜菜碱、维生素及电解质离子复合添加剂。

1.3 试验饲粮与饲养管理

试验饲粮以全混合日粮(total mixed ration,TMR)形式饲喂。试验牛每天饲喂3次(08:00、15:00、22:00),产后每天机械挤奶3次(07:00、14:00、21:00)。基础饲粮参照NRC(2001)奶牛饲养标准与养殖场实际生产水平配制,其组成及营养水平见表2。每次投料时甜菜碱、维生素及电解质离子复合添加剂与部分饲粮(1 kg左右)均匀混合后先行饲喂,待该部分饲粮被完全采食后投喂剩余饲粮,保证甜菜碱、维生素及电解质离子复合添加剂采食完全。试验牛饲养管理参照养殖场规程执行。
表2 基础饲粮组成及营养水平(干物质基础)

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

项目
Items		 围产期
Peripartum
period		 泌乳前期
Early lactation
period
原料Ingredients
玉米青贮Corn silage 57.89 33.44
苜蓿干草Alfalfa hay 13.49
小麦秸秆Wheat straw 17.85
玉米Corn 7.29 23.63
麸皮Wheat bran 3.88
糖蜜Molasses 3.13
豆粕Soybean meal 3.15 11.43
棉籽粕Cottonseed meal 3.64 2.67
菜籽粕Rapeseed meal 2.91 1.91
胡麻饼Flaxseed cake 2.42 1.14
全棉籽Whole cottonseed 5.69
石粉Limestone 0.24 0.61
磷酸氢钙CaHPO4 0.24 0.42
小苏打NaHCO3 1.03
氯化钠NaCl 0.24 0.61
预混料Premix1) 0.25 0.61
氧化镁MgO 0.19
合计Total 100.00 100.00
营养水平Nutrient levels2)
产奶净能NEL/(MJ/kg) 6.40 6.86
粗蛋白质CP 12.21 16.81
中性洗涤纤维NDF 45.12 28.72
有效中性洗涤纤维peNDF 40.80 24.12
酸性洗涤纤维ADF 25.43 17.80
粗灰分Ash 6.40 9.04
钙Ca 0.54 0.91
磷P 0.38 0.43

1)每千克预混料含 Per kilogram of the premix contained:VA 200 000 IU,VD3 30 000 IU,VE 4 000 mg,烟酸 nicotinic acid 3 900 mg,Cu 1 000 mg,Fe 1 500 mg,Mn 1 200 mg,Zn 4 000 mg,I 50 mg,Se 25 mg,Co 30 mg。

2)产奶净能、有效中性洗涤纤维为计算值,其余为实测值。NEL and peNDF were calculated values, while the others were measured values.

1.4 样品采集和分析

1.4.1 牛舍内温度、相对湿度测定及温湿度指数(temperature and humidity index,THI)计算

试验期每天06:00、10:00、14:00、18:00和22:00测定位于牛舍前、后4个固定点(距离地面1.5 m)的温度和相对湿度,计算THI,计算公式如下:
THI=0.81T+(0.99T-14.37)RH+46.3。
式中:T为每天平均温度(℃);RH为每天平均相对湿度(%)。
参考Zimbelman等[15]的描述,THI=68为奶牛出现热应激的阈值,因此,当THI>68时表示处于热应激环境。

1.4.2 呼吸频率、直肠温度测定

在产前第21、14和7天,产后第0(产犊当天)、7、14、21、35、49和63天的14:00测定每头牛每分钟腹部与胸廓起伏次数作为呼吸频率,连续测定2次取平均值。用兽用体温计测定试验牛直肠温度,连续测定2次取平均值。

1.4.3 DMI、产奶量及乳成分测定

奶牛产前第14和7天,产后第7、14、21、35、49和63天分别记录早、中、晚投料量和剩料量。同时,采用四分法采集饲料样,测定干物质含量并计算DMI。产后每7 d记录试验牛产奶量4次,每次间隔1 d。并于产后第7、14、21、35、49和63天早、中、晚各采集50 mL奶样,按4∶3∶3比例混合均匀,用全自动乳成分分析仪(MilkoScan-FT120,FOSS)测定乳脂率、乳蛋白率、乳糖率和乳总固形物含量,并计算4%校正乳(fat-corrected milk,FCM)产量。4%FCM产量计算公式如下:
4%FCM产量=0.4M+15F。
式中:M为产奶量(kg/d);F为乳脂产量(kg/d)。

1.4.4 血清生化指标测定

在产前第14天、产后第21和63天晨饲前,每组随机选取6头牛进行尾静脉采血(10 mL),于3 000×g离心15 min,制备血清样品,分装于1.5 mL离心管,-20 ℃保存待测。谷胱甘肽过氧化物酶(glutathione peroxidase,GSH-Px)、超氧化物歧化酶(superoxide dismutase,SOD)、过氧化氢酶(catalase,CAT)活性和总抗氧化能力(total antioxidant capacity,T-AOC)使用试剂盒(南京建成生物工程研究所)检测。免疫球蛋白A(immunoglobulin A,IgA)、免疫球蛋白M(immunoglobulin M,IgM)、免疫球蛋白G(immunoglobulin G,IgG)、游离脂肪酸(nonestesterified fatty acid,NEFA)、β-羟丁酸(β-hydroxybutyric acid,BHBA)使用酶联免疫吸附测定试剂盒(美国TSZ公司)检测。谷丙转氨酶(alanine aminotransferase,ALT)、谷草转氨酶(aspartate aminotransferase,AST)、碱性磷酸酶(alkaline phosphatase,ALP)活性和葡萄糖(glucose,GLU)、总胆红素(total bilirubin,T-BIL)、总蛋白(total protein,TP)、白蛋白(albumin,ALB)、球蛋白(globulin,GLB)含量通过日立7600型全自动生化仪(日本日立公司)测定,并计算白蛋白/球蛋白(albumin/globulin,A/G)。

1.5 数据分析

试验数据使用SPSS 26.0软件对试验数据进行单因素方差分析,试验结果用平均值和均值标准误(SEM)表示。P≤0.05表示差异显著,0.05<P≤0.10表示具有显著趋势,P>0.10表示差异不显著。

2 结果

2.1 牛舍THI

如图1所示,产前21 d至产后63 d牛舍THI均高于68,表明牛群处于热应激环境。
图1 牛舍温湿度指数

Fig.1 THI of cowshed

2.2 甜菜碱、维生素及电解质离子复合添加剂对奶牛直肠温度和呼吸频率的影响

由表3可知,CA组围产期和试验全期奶牛呼吸频率显著低于CON组(P<0.05)。2组之间围产期、泌乳前期和试验全期奶牛直肠温度无显著差异(P>0.10)。
表3 甜菜碱、维生素及电解质离子复合添加剂对奶牛直肠温度和呼吸频率的影响

Table 3 Effects of betaine, vitamins and electrolyte ions compound additive on rectal temperature and respiratory rate of dairy cows

项目
Items		 对照组
CON group		 添加剂组
CA group		 SEM P值
P-value
围产期(产前第21天至产后第21天) Peripartum period (day 21 before delivery to day 21 after delivery)
直肠温度Rectal temperature/℃ 38.80 38.75 0.035 0.500
呼吸频率Respiratory rate/(次/min) 68.41 65.25 0.764 0.036
泌乳前期(产后第22~63天) Early lactation period (days 22 to 63 after delivery)
直肠温度Rectal temperature/℃ 38.46 38.39 0.035 0.314
呼吸频率Respiratory rate/(次/min) 56.38 55.09 0.530 0.230
试验全期(产前第21天至产后第63天) Whole experiment period (day 21 before delivery to day 63 after delivery)
直肠温度Rectal temperature/℃ 38.69 38.64 0.028 0.325
呼吸频率Respiratory rate/(次/min) 64.80 62.20 0.534 0.012

2.3 甜菜碱、维生素及电解质离子复合添加剂对奶牛生产性能的影响

由表4可知,在围产期,CA组奶牛DMI显著高于CON组(P<0.05);与CON组相比,CA组乳糖率有提高的趋势(P=0.073);2组之间奶牛产奶量、乳脂率、乳蛋白率、乳总固形物含量及4%FCM产量无显著差异(P>0.10)。在泌乳前期,CA组奶牛DMI和产奶量显著高于CON组(P<0.05);与CON组相比,CA组4%FCM产量有提高的趋势(P=0.090);2组之间乳糖率、乳脂率、乳蛋白率、乳总固形物含量没有显著差异(P>0.10)。在试验全期,CA组奶牛DMI和4%FCM产量显著高于CON组(P<0.05);与CON组相比,CA组奶牛产奶量(P=0.062)、乳蛋白率(P=0.086)和总固形物率(P=0.093)有提高的趋势;2组之间乳脂率和乳糖率无显著差异(P>0.10)。
表4 甜菜碱、维生素及电解质离子复合添加剂对奶牛生产性能的影响

Table 4 Effects of betaine, vitamins and electrolyte ions compound additive on performance of dairy cows

项目
Items		 对照组
CON group		 添加剂组
CA group		 SEM P值
P-value
围产期(产前第21天至产后第21天) Peripartum period (day 21 before delivery to day 21 after delivery)
干物质采食量DMI/(kg/d) 15.72 16.31 0.093 0.001
产奶量Milk yield/(kg/d) 24.13 25.81 0.760 0.271
乳脂率Milk fat rate/% 2.95 3.17 0.078 0.178
乳蛋白率Milk protein rate/% 3.27 3.39 0.042 0.163
乳糖率Milk lactose rate/% 4.67 4.37 0.082 0.073
乳总固形物含量Milk total solids content/% 12.14 12.34 0.133 0.463
4%校正乳4%FCM/(kg/d) 20.38 22.71 0.833 0.165
泌乳前期(产后第22~63天) Early lactation period (days 22 to 63 after delivery)
干物质采食量DMI/(kg/d) 18.39 18.99 0.138 0.026
产奶量Milk yield/(kg/d) 28.47 30.98 0.626 0.043
乳脂率Milk fat rate/% 3.04 3.09 0.085 0.765
乳蛋白率Milk protein rate/% 3.02 3.08 0.025 0.196
乳糖率Milk lactose rate/% 5.12 5.18 0.033 0.434
乳总固形物含量Milk total solids content/% 11.16 11.27 0.108 0.618
4%校正乳4%FCM/(kg/d) 24.37 26.83 0.725 0.090
试验全期(产前第21天至产后第63天) Whole experiment period (day 21 before delivery to day 63 after delivery)
干物质采食量DMI/(kg/d) 16.72 17.31 0.103 0.002
产奶量Milk yield/(kg/d) 27.02 29.26 0.601 0.062
乳脂率Milk fat rate/% 3.00 3.13 0.053 0.220
乳蛋白率Milk protein rate/% 3.14 3.24 0.028 0.086
乳糖率Milk lactose rate/% 4.90 4.78 0.042 0.151
乳总固形物含量Milk total solids content/% 11.69 11.90 0.060 0.093
4%校正乳4%FCM/(kg/d) 22.97 25.47 0.628 0.044

2.4 甜菜碱、维生素及电解质离子复合添加剂对奶牛能量平衡指标的影响

由表5可知,CA组产前第14天、产后第63天奶牛血清NEFA含量显著低于CON组(P<0.05);与CON组相比,CA组产后第21天血清NEFA含量有降低的趋势(P=0.100)。与CON组相比,CA组产后第63天血清GLU含量有提高的趋势(P=0.070)。
表5 甜菜碱、维生素及电解质离子复合添加剂对奶牛能量平衡指标的影响

Table 5 Effects of betaine, vitamins and electrolyte ions compound additive on energy balance indexes of dairy cows

项目
Items		 对照组
CON group		 添加剂组
CA group		 SEM P值
P-value
产前第14天Day 14 before delivery
游离脂肪酸NEFA/(μmol/L) 346.36 280.99 12.969 0.004
β-羟丁酸BHBA/(μmol/L) 14.22 12.40 0.649 0.171
葡萄糖GLU/(mmol/L) 3.40 3.69 0.182 0.457
产后第21天Day 21 after delivery
游离脂肪酸NEFA/(μmol/L) 355.00 309.25 14.079 0.100
β-羟丁酸BHBA/(μmol/L) 11.89 11.15 0.548 0.529
葡萄糖GLU/(mmol/L) 3.27 3.02 0.099 0.210
产后第63天Day 63 after delivery
游离脂肪酸NEFA/(μmol/L) 349.48 295.05 11.038 0.006
β-羟丁酸BHBA/(μmol/L) 13.21 11.99 0.529 0.267
葡萄糖GLU/(mmol/L) 3.04 3.54 0.140 0.070

2.5 甜菜碱、维生素及电解质离子复合添加剂对奶牛血清肝脏功能指标的影响

由表6可知,CA组产前第14天血清AST活性显著低于CON组(P<0.05),产后第21天血清ALB含量显著高于CON组(P<0.05),产后第63天血清T-BIL含量显著低于CON组(P<0.05);与CON组相比,CA组产后第21天血清A/G有上升的趋势(P=0.066)。
表6 甜菜碱、维生素及电解质离子复合添加剂对奶牛血清肝脏功能指标的影响

Table 6 Effects of betaine, vitamins and electrolyte ions compound additive on serum liver function indexes of dairy cows

项目
Items		 对照组
CON group		 添加剂组
CA group		 SEM P值
P-value
产前第14天Day 14 before delivery
谷丙转氨酶ALT/(U/L) 19.67 15.17 1.373 0.103
谷草转氨酶AST/(U/L) 67.33 49.83 3.694 0.009
白蛋白ALB/(g/L) 35.00 34.88 0.570 0.924
球蛋白GLB/(g/L) 47.50 44.33 2.500 0.552
白蛋白/球蛋白A/G 0.76 0.82 0.045 0.524
总蛋白TP/(g/L) 82.32 79.25 2.320 0.535
碱性磷酸酶ALP/(U/L) 52.83 46.33 4.727 0.518
总胆红素T-BIL/(μmol/L) 0.67 1.00 0.265 0.554
产后第21天Day 21 after delivery
谷丙转氨酶ALT/(U/L) 18.67 18.33 1.145 0.892
谷草转氨酶AST/(U/L) 86.83 77.67 5.280 0.411
白蛋白ALB/(g/L) 31.40 34.12 0.689 0.042
球蛋白GLB/(g/L) 48.67 46.67 1.725 0.587
白蛋白/球蛋白A/G 0.65 0.75 0.028 0.066
总蛋白TP/(g/L) 79.97 80.63 1.952 0.874
碱性磷酸酶ALP/(U/L) 40.00 32.33 2.474 0.126
总胆红素T-BIL/(μmol/L) 1.80 0.67 0.440 0.213
产后第63天Day 63 after delivery
谷丙转氨酶ALT/(U/L) 20.83 20.50 2.301 0.946
谷草转氨酶AST/(U/L) 76.17 69.17 3.909 0.396
白蛋白ALB/(g/L) 30.80 31.88 0.903 0.574
球蛋白GLB/(g/L) 57.33 59.50 2.770 0.715
白蛋白/球蛋白A/G 0.55 0.56 0.040 0.856
总蛋白TP/(g/L) 88.10 91.30 7.892 0.509
碱性磷酸酶ALP/(U/L) 42.50 33.33 3.187 0.159
总胆红素T-BIL/(μmol/L) 1.53 0.42 0.272 0.032

2.6 甜菜碱、维生素及电解质离子复合添加剂对奶牛血清健康指标的影响

由表6可知,CA组产前第14天血清CAT活性显著高于CON组(P<0.05);与CON组相比,CA组产后第21天血清IgG含量有提高的趋势(P=0.090),产后第63天血清IgM含量有降低的趋势(P=0.074)。
表7 甜菜碱、维生素及电解质离子复合添加剂对奶牛血清健康指标的影响

Table 7 Effects of betaine, vitamins and electrolyte ions compound additive on serum health indexes of dairy cows

项目
Items		 对照组
CON group		 添加剂组
CA group		 SEM P值
P-value
产前第14天Day 14 before delivery
免疫球蛋白A IgA/(μg/mL) 130.08 115.12 9.934 0.478
免疫球蛋白G IgG/(μg/mL) 333.33 370.33 13.311 0.175
免疫球蛋白M IgM/(μg/mL) 78.15 66.86 5.057 0.285
超氧化物歧化酶SOD/(U/mL) 162.76 168.86 3.106 0.351
谷胱甘肽过氧化氢酶GSH-Px/(U/mL) 33.85 43.85 3.872 0.211
过氧化氢酶CAT/(U/mL) 0.70 1.19 0.117 0.029
总抗氧化能力T-AOC/(mmol/L) 0.58 0.60 0.030 0.866
产后第21天Day 21 after delivery
免疫球蛋白A IgA/(μg/mL) 132.16 132.40 10.777 0.992
免疫球蛋白G IgG/(μg/mL) 363.89 400.56 10.823 0.090
免疫球蛋白M IgM/(μg/mL) 75.43 68.61 6.140 0.603
超氧化物歧化酶SOD/(U/mL) 149.31 156.20 4.844 0.504
谷胱甘肽过氧化氢酶GSH-Px/(U/mL) 69.23 93.85 9.114 0.189
过氧化氢酶CAT/(mmol/mL) 1.48 1.48 0.121 0.976
总抗氧化能力T-AOC/(U/L) 0.73 0.73 0.040 0.974
产后第63天Day 63 after delivery
免疫球蛋白A IgA/(μg/mL) 149.98 146.74 5.728 0.792
免疫球蛋白G IgG/(μg/mL) 388.89 420.83 18.010 0.401
免疫球蛋白M IgM/(μg/mL) 78.46 64.59 3.920 0.074
超氧化物歧化酶SOD/(U/mL) 157.46 158.65 5.824 0.924
谷胱甘肽过氧化氢酶GSH-Px/(U/mL) 65.38 82.31 6.249 0.188
过氧化氢酶CAT/(U/mL) 2.05 2.48 0.200 0.305
总抗氧化能力T-AOC/(mmol/L) 0.68 0.64 0.039 0.594

3 讨论

3.1 甜菜碱、维生素及电解质离子复合添加剂对奶牛直肠温度和呼吸频率的影响

热应激时,奶牛首先通过加快呼吸频率增加散热,当呼吸散热不足以缓解热应激时直肠温度升高,因此呼吸频率和直肠温度是评价奶牛热应激的2个重要指标[4]。THI结果显示,产前第21天至产后第63天奶牛处于热应激环境,此时奶牛通过加快呼吸频率快速散热。本研究结果表明补饲甜菜碱、维生素及电解质离子复合添加剂可降低围产期和试验全期奶牛呼吸频率。这可能是甜菜碱、维生素及电解质离子复合添加剂中的甜菜碱和电解质离子作为渗透压调节剂减少了离子泵的能量消耗,进而降低奶牛基础热量的产生[16]。

3.2 甜菜碱、维生素及电解质离子复合添加剂对奶牛生产性能的影响

围产前期胎儿快速生长挤压瘤胃,围产后期奶牛需经历饲粮结构变化、分娩、泌乳启动等应激导致DMI下降。同时,夏季热应激可能延长食糜过胃时间,通过胃伸张感受器作用于下丘脑厌食中枢,引起厌食反馈,进一步降低围产期和泌乳前期DMI[17]。产后奶牛需要维持泌乳和恢复体况,但此阶段干物质摄入不足,导致产奶量下降和体况恢复减缓。本研究表明补饲复合添加剂可提高夏季围产期和泌乳前期奶牛DMI,且有提高产奶量和乳蛋白率的趋势。本研究中产奶量的提高可能与DMI的增加和营养物质利用率提高相关。本研究未测定营养物质消化率和瘤胃发酵参数,但Mahmood等[18]通过体外试验明确甜菜碱可提高瘤胃发酵水平和营养物质利用率。Shah等[19]研究表明,热应激条件下添加甜菜碱(15 g/d)可增加奶牛DMI、产奶量,改善瘤胃发酵和提高营养物质消化率。Dunshea等[20]研究发现,放牧奶牛补饲甜菜碱(15 g/d)可提高产奶量和瘤胃发酵水平。前期研究表明,甜菜碱可缓解热应激,促进食欲,提高奶牛DMI,改善泌乳性能[19,21]。甜菜碱还有利于维持乳腺细胞的正常结构和生物活性,降低热应激导致的氧化应激损伤,对热应激条件下产奶量的提高提供保障[22]。
大量研究表明补饲维生素可通过改善奶牛健康提高泌乳性能。泌乳期奶牛的乳腺上皮细胞处于高代谢状态,极易产生大量活性氧和脂质过氧化物,导致细胞发生氧化应激。维生素A、维生素C和维生素E可清除自由基缓解氧化应激,降低乳腺细胞损伤,保障乳腺健康。Jin等[23]研究发现,高剂量维生素A(220 IU/kg体重 vs. 110 IU/kg体重)可提高奶牛抗氧化能力和免疫力,且有提高奶牛产奶量、乳脂率和乳蛋白率的趋势。同时,研究表明补饲B族维生素和抗坏血酸可提高奶牛泌乳性能[24]。Golder等[25]研究发现,奶牛围产期和泌乳前期添加维生素D3可改善奶牛健康,并提高产奶量和乳蛋白率。
同时,研究表明Na+、K+、氯离子(Cl-)等电解质离子可缓解热应激时电解质流失导致的阴阳离子失衡,维持细胞渗透压平衡,促进瘤胃有益微生物生长,提高营养物质利用率,提高DMI和产奶量[26]。本试验乳蛋白率提高的原因可能是甜菜碱作为甲基供体时有类似蛋氨酸的作用,通过减少蛋氨酸转甲基作用使蛋氨酸合成乳蛋白增多[5,27]。因此,甜菜碱、维生素及电解质离子复合添加剂可能通过提高DMI、改善营养物质利用率和促进乳腺健康等多方面协同作用,提高热应激下奶牛泌乳性能。

3.3 甜菜碱、维生素及电解质离子复合添加剂对奶牛能量平衡指标的影响

围产期和泌乳前期奶牛DMI降低,为缓解能量摄入不足,机体通过脂肪动员加强肝脏糖异生供应能量,大量动用体脂导致NEFA释放入血液[3],血液NEFA含量随之升高。NEFA一方面进入乳腺合成乳脂,另一方面进入肝脏进行代谢,NEFA在肝脏中完全氧化生成二氧化碳(CO2)和水(H2O),不完全氧化生成酮体(主要为BHBA)。当机体发生NEB时,大量NEFA不完全氧化生成BHBA,导致血液BHBA含量升高[3]。因此,血液NEFA、BHBA和GLU含量是反映奶牛能量平衡状态的关键指标。Shah等[19]和Wang等[28]研究发现,饲粮中添加甜菜碱可降低血液NEFA和BHBA含量,提高血液GLU含量。与前期结果相似,本研究发现补饲复合添加剂可降低奶牛血清NEFA含量,且有提高产后第63天血清GLU含量的趋势,表明甜菜碱、维生素及电解质离子复合添加剂可缓解NEB。原因可能是补饲甜菜碱、维生素及电解质离子复合添加剂后奶牛DMI提高,养分和能量摄入增加,减少了脂质动员,NEFA生成降低。甜菜碱可通过肝脏合成肉碱,增强脂肪酸转运,促进细胞脂肪酸β-氧化,降低脂肪酸累积[29-30]。同时,甜菜碱还作为甲基供体参与磷脂合成,促进脂肪酸氧化吸收[5]。

3.4 甜菜碱、维生素及电解质离子复合添加剂对奶牛血清肝脏功能指标的影响

血液AST、ALT、ALB、T-BIL是反映肝脏损伤的重要指标[3]。AST主要存在于肝细胞的线粒体内,而ALT主要分布于肝细胞的胞浆内,肝细胞受损导致线粒体损伤时,导致血液AST和ALT活性升高[31]。ALB在肝脏中合成,对维持血浆胶体渗透压和物质转运有重要作用,肝脏受损伤时会导致ALB含量减少,同时还会影响胆红素的代谢,导致血液中胆红素累积[32]。本试验发现,补饲甜菜碱、维生素及电解质离子复合添加剂可缓解肝脏损伤,其原因可能是在甜菜碱、维生素和电解质离子的协同作用下,肝脏细胞抗氧化能力得到提高,且脂质代谢产物在肝脏细胞内堆积减少。甜菜碱作为高效甲基供体参与一碳代谢,具有促进磷脂酰胆碱、谷胱甘肽和牛磺酸合成的作用[7]。磷脂酰胆碱参与合成极低密度脂蛋白,减少甘油三酯在肝脏大量累积导致肝脏损伤,谷胱甘肽和牛磺酸具有抗氧化功能可保护肝脏细胞免受活性氧的损害[5]。维生素A和维生素E可提高肝脏细胞抗氧化能力,减少脂质代谢产生的活性氧对肝脏细胞的损害[8,12]。Seifzadeh等[10]研究表明,奶牛产前补饲维生素C(20 g/d)可降低血清AST活性,但对血清ALT活性没有影响。Na+、K+、Cl-等电解质离子可通过维持细胞内外渗透压平衡减少热应激对肝脏细胞损伤。

3.5 甜菜碱、维生素及电解质离子复合添加剂对奶牛血清健康指标的影响

围产期奶牛要经历分娩、换料、泌乳启动、高温等应激,机体免疫功能下降,处于不同程度的免疫抑制状态[1]。本研究发现,补饲甜菜碱、维生素及电解质离子复合添加剂有提高奶牛产后第21天血清IgG含量的趋势,表明该复合添加剂可改善围产后期奶牛的免疫功能。免疫指标的变化可能主要来源于维生素对免疫功能的调节[33]。维生素A可通过加强体内T细胞和B细胞协同作用,提高免疫球蛋白合成[34]。维生素C可调节机体免疫功能,促进B细胞与T细胞增殖分化和IgM、IgG等抗体合成[35]。维生素E可通过抑制炎症因子的产生提高体液免疫功能[36]。马露[37]研究发现,联合添加维生素A和维生素E可提高泌乳奶牛血清IgG和IgM含量。曹荣[38]研究表明,补饲维生素D3有提高围产期奶牛血清IgM含量的趋势。但本试验发现,补饲甜菜碱、维生素及电解质离子复合添加剂有降低奶牛产后第63天血清IgM含量的趋势,其原因尚不明晰,需进一步研究。
围产期和泌乳前期奶牛脂质代谢增强,自由基积累增加,当机体抗氧化体系不足以清除自由基时发生氧化应激。T-AOC、CAT、GSH-Px、SOD是机体抗氧化能力的重要指标。本研究发现,补饲甜菜碱、维生素及电解质离子复合添加剂可提高机体抗氧化能力。甜菜碱和Mg2+可通过恢复SOD和CAT活性并降低脂质过氧化终产物含量,缓解热应激导致的抗氧化能力下降[13,22]。同时,甜菜碱可参与甲硫氨酸循环,生成具有抗氧化活性的牛磺酸和谷胱甘肽,清除自由基缓解细胞氧化应激[5]。维生素A作为转录调节剂可生成全反式视黄酸,介导抗氧化相关基因表达,促进抗氧化物合成[8]。维生素C和维生素E为体内外源抗氧化剂,可有效清除活性氧,增强抗氧化能力[10,12]。因此,补饲甜菜碱、维生素及电解质离子复合添加剂可能通过甜菜碱、维生素和电解质离子协同作用,提高抗氧化酶活性,增强机体抗氧化能力。

4 结论

夏季补饲甜菜碱、维生素及电解质离子复合添加剂可缓解围产期和泌乳前期奶牛热应激和NEB,提高生产性能,并改善围产期奶牛机体免疫功能和抗氧化能力。

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