共轭亚油酸对基因表达的影响研究进展

共轭亚油酸(Conjugated Linoleic Acid,CLA)是一类含有共轭双键的亚油酸衍生的异构体混合物。是普遍存在于人和动物体内的营养物质。CLA作为重要的营养素,其对基因表达的影响在动物领域也相当火热。本文拟在对近几年来CLA影响基因表达的研究作一综述。     

意大利荷斯坦弗里斯兰奶牛的共轭亚油酸、选择的乳脂肪酸和乳脂肪酸不饱和度的遗传参数

本研究的目的是评估意大利荷斯坦弗里斯兰奶牛群的共轭亚油酸、其它选择的乳脂肪酸及其不饱和度的遗传参数。此外，还要考虑牛乳中脂肪酸、乳脂及乳蛋白之间的相互关系。从位于意大利东北部的34个商业牛群中54个半同胞家族的990头奶牛中随机抽取样品。对每个样品进行乳脂、乳蛋白质及单种脂肪酸的百分率分析（像计算总脂肪重量的比例一样计算单种脂肪酸重量）。不饱和脂肪酸的遗传可能性适中，从C16：1的0．14到C14：1的0．19。每种不饱和脂肪酸的遗传可能性都要小于10％。去饱和脂肪酸、单不饱和脂肪酸及共轭亚油酸／tran~1118：1比例的指数的遗传可能性分别为0．15、0．14和0．15。遗传可能性价值标准差的范围为0．02～0．06。C16：0与C18：0，C14：0与C18：0之间均呈很高的负遗传相关。去饱和度指数与C14；0及C16：0之间也呈很高的负遗传相关（分别为-0.70和-0．72），然而与C18：0之间的遗传相关则接近于0（0．03）。C16：0与脂肪百分率之间的遗传相关呈正值（0．74），意味着脂肪百分率的选择会导致与C16：0相关性的增加，然而，trans—11 C18：1与cis-9及trans-11C18：2含量之间的遗传相关随着脂肪百分率的增加而下降（分别为-0．69和-0．55）。脂肪百分率与14：1／14及16：1／16比例之间的遗传相关为正值，而与18：1／18及共轭亚油酸／trans-11 18：1比例之间的遗传相关为负值。这些结果说明通过基因选择有可能改变牛乳中的脂肪酸组成，这将满足消费者对牛乳及乳制品健康安全方面的要求。     

瘤胃保护共轭亚油酸和亚油酸对奶牛产奶性能的影响

选择健康、泌乳月份与产奶量相近的多胎荷斯坦泌乳牛20头,随机分成5组,每组4头,研究日粮中添加商业来源的瘤胃保护共轭亚油酸钙盐(Ca-CLA)同时添加自然来源亚油酸(葵花油)对奶牛生产性能的影响。试验期为52d。对照组基础日粮为60%粗饲料(苜蓿、羊草、青贮)和40%精料(以DM为基础),处理组在对照组日粮基础上分别添加Ca-CLA100g/d·头(CLA)、葵花油350g/d·头(Sunf);Ca-CLA100g/d·头 葵花油350g/d·头(CLA Sunf),Ca-CLA50g/d·头 葵花油175g/d·头(1/2CLA 1/2Sunf)。结果表明:在奶牛日粮中,单独添加自然来源亚油酸产奶量较对照组差异不显著(P>0.05),而单独添加共轭亚油酸钙盐或与自然来源亚油酸高低不同剂量添加产奶量较对照组都分别显著提高2.20%、9.95%、11.16%,无论单独添加自然来源亚油酸或Ca-CLA或二者以高低不同剂量同时添加,牛奶的乳脂率较对照组都分别显著降低15.0%,6.24%,21.74%,14.35%。总之,奶牛日粮中同时添加Ca-CLA和自然来源亚油酸能显著提高产奶量,降低乳脂率,并且,减少Ca-CLA的添加量同时添加自然来源亚油酸可以达到高剂量添加Ca-CLA相同的效果。     

共轭亚油酸对泌乳奶牛乳脂的影响

本文对日粮中添加或真胃灌注CLA对奶牛乳脂、乳脂合成及血液指标等方面的影响进行了简述。     

利用牛乳汁体细胞研究乳腺免疫相关因子的表达

利用乳汁体细胞分子生物学技术平台,以奶牛初乳和末乳为研究对象,看家基因GAPDH为内参,对乳汁中IL-8、CCL5、CXCL14、κ-CN和α-LA进行半定量RT-PCR分析。结果显示,在209、202、376、151、233bp位置分别出现5种基因预期大小的特异性扩增条带。乳中IL-8、CCL5、CXCL14、κ-CN和α-LA mRNA转录水平的相对定量结果表明,与初乳相比,末乳中IL-8和α-LA mRNA的转录水平显著降低（P〈0.05）,CCL5、CXCL14和κ-CN mR-NA的转录水平分别下降21%、40%和37%,差异不显著（P〉0.05）。结果提示,末乳期奶牛乳腺免疫功能下降,应加强此阶段的管理,降低乳房炎的发生。     

共轭亚油酸对猪营养的作用

共轭亚油酸 (Ｃｏｎｊｕｇａｔｅｄｌｉｎｏｌｅｉｃａｃｉｄ ,ＣＬＡ)是一系列含有碳碳共轭双键、具有位置和几何异构的十八碳二烯酸构成的。ＣＬＡ具有 16种共轭亚油酸的异构物 ,9,11-ＣＬＡ在自然界的分布丰度相对较高 ,在ＣＬＡ异构体中 ,活性是按以下顺序递减的 :9ｃ ,11ｔ>10ｔ,12ｃ >9ｔ,11ｔ,因此 9ｃ,11ｔ—ＣＬＡ可能是其中最有效的异构体。自Ｐａｒｉｚａ等从研磨的牛肉中发现ＣＬＡ以来 ,相继发现ＣＬＡ对实验动物具有抗癌 (Ｓｃｉｍｅｃａ等 ,1994 ;Ｐａｒｉｚａ,1997)、抗动脉粥样硬化 (Ｐａｒｏｄｉ,1999;Ｇｉｌｌｍａｎ等 ,…     

牛乳腺脂肪合成关键酶基因在乳汁体细胞中的表达研究

为了阐明乳脂合成的影响因素及其内在分子机理,为反刍动物原料乳的优化,特别是为乳脂肪的营养调控和遗传改良提供理论依据。本试验以奶牛初乳、常乳和末乳中的乳汁体细胞为研究对象,以看家基因GAPDH为内参,对初乳、常乳和末乳中LPL、CD36、VLDLR、ACSS2、ACSL1、FABP3、ACC、FASN、SCD、ADFP、XDH和BTN1A1 mRNA进行半定量RT-PCR分析。结果发现,LPL、CD36、VLDLR、ACSS2、ACSL1、FABP3、SCD、AD-FP、XDH和BTN1A1 mRNA在初乳、常乳和末乳中均有表达,而ACC和FASNmRNA只在初乳中表达,常乳和末乳中均不表达;半定量结果表明,与初乳相比,常乳和末乳中LPL、CD36、VLDLR、ACSS2、ACSL1、FABP3、SCD、ADFP、XDH和BTN1A1 mRNA转录水平显著降低(P<0.05),且常乳与末乳间差异不显著(P>0.05)。研究结果提示初乳期乳腺脂肪合成能力明显高于常乳和末乳期乳腺,且脂肪合成关键酶基因的表达与细胞内脂转运和代谢的生理变化有关。     

共轭亚油酸对奶牛产奶量及乳品质的影响

试验选用体况相近的健康泌乳奶牛48头,采用单因子随机化设计,分4组。对照组饲喂基础日粮,试验组在基础日粮基础上添加共轭亚油酸分别为15g/d·头、30g/d·头、45g/d·头。结果表明:(1)在日粮中添加共轭亚油酸可使奶牛产奶量提高,添加量为30g/d·头和45g/d·头时分别比对照组提高了18.9%和17.1%(P<0.05)。(2)在日粮中添加共轭亚油酸可使牛奶乳脂率下降,添加量为30g/d·头和45g/d·头时分别比对照组下降了12.3%和10.5%(P<0.05)。     

共轭亚油酸的降脂功能及其对生化参数的影响

本文简要阐述了共轭亚油酸(CLA)的来源、结构特点及提高动物产品中CLA含量的营养调控途径，并重点综述了共轭亚油酸降低动物及人体脂肪沉积的生理效应极其对有关生化参数的影响。     

乳脂肪中共轭亚油酸的生理活性研究

乳脂肪是由一个甘油分子和三个脂肪酸分子组成的甘油三酸酯的混合物。它占乳脂类的97%～99%,具有良好的风味和消化性,且所含的生理活性物质较多,共轭亚油酸作为乳脂肪的生理活性物质之一,具有多种生理功能,它在人体免疫调节、抑癌和降血脂及防治心血管疾病等方面有重要作用。本文对乳脂肪中共轭亚油酸来源、作用及机制进行了分析,阐述了共轭亚油酸作为一种新型营养物质的可能,并树立了人们对脂肪的正确消费观念。     

Comparison between stearoyl‐CoA desaturase expression in milk somatic cells and in mammary tissue of lactating dairy cows

Stearoyl‐CoA desaturase (SCD) is an important enzyme in the bovine mammary gland, where it inserts a cis‐double bond at the Δ9 position in a wide range of fatty acids. Investigating SCD expression in the bovine mammary gland generally requires invasive biopsy to obtain mammary tissue. The aim of this study was to evaluate the use of milk somatic cells as a non‐invasive alternative to biopsy for measuring mammary SCD expression in dairy cows. Both milk somatic cells and mammary tissue were collected from 14 Holstein‐Friesian cows and used for analysis of SCD expression by real‐time PCR. The SCD5 mRNA levels in mammary tissue compared with SCD1 were low, and for several milk somatic cell samples, SCD5 expression was even below the limit of detection. A significant relationship was found between SCD1 expression in milk somatic cells and in mammary tissue. In addition, SCD1 expression in milk somatic cells was significantly related to Δ9‐desaturase indices in milk, which are commonly used as an indicator of SCD1 activity within the mammary gland. Our study showed that milk somatic cells can be used as a source of mRNA to study SCD1 expression in dairy cows, offering a non‐invasive alternative to mammary tissue samples obtained by biopsy.     

Effect of brewer's grain on rumen fermentation, milk production and milk composition in lactating dairy cows

Six lactating Holstein cows were divided into two groups (n = 3) and used in a double reversal trial with three periods of 14 days each to evaluate the rumen fermentation, milk production and milk composition of cows fed brewer's grain (BG). The control diets contained 14% chopped Sudangrass hay, 24% corn silage, 18% alfalfa hay cube, 34% concentrate mixture‐1 and 10% concentrate mixture‐2 (wheat bran, soybean meal and cottonseed). In the experimental diet, wet BG replaced the concentrate mixture‐2. The protozoal population, concentration of ammonia‐N and volatile fatty acids in the ruminal fluid did not differ between the control and BG diets. The molar percentage of acetic acid was significantly higher (P < 0.05) with the BG diet at 5 h after feeding. The milk yield, the percentage of protein, lactose, solids not‐fat and somatic cell counts of milk did not differ between the two diets. The percentage of milk fat tended to increase with the BG diet. The BG diet significantly increased the proportions of C18:0 and C18:1 in milk fat (P < 0.01, P < 0.05, respectively) and tended to increase that of conjugated linoleic acid.     

Variation in somatic cell counts of milk samples from individual cows

Somatic cell counts of 2570 milk samples from 765 cows collected bimonthly from November 1975 to May 1976 were transformed to logarithmic values and analysed statistically. Components of variance were estimated as follows: Herds 0.033 (13 %), age groups 0.021 (8%), cows (within herds and age groups) 0.080 (31%), months 0.014 (6%), residual 0.107 (42%). Correction of actual cell counts for the influence of milk yield on the day of sampling led to only small changes in the magnitude of the various components. The coefficient of correlation between samples from the same cow was computed as 0.60 when the samples were from the same lactation, and 0.37 for samples from consecutive lactations.The proportionately small variation among herds as compared to the variation among cows of the same herd throws doubt on the efficiency of cell counting in samples of herd milk as a way of identifying cows with high cell counts.     

改善牛乳脂中共轭亚油酸含量的研究

自从发现共轭亚油酸特殊的生理作用以来,共轭亚油酸就一直是动物营养、药物及食品等研究领域的一个热点,目前对于含有共轭亚油酸的功能性食品的研究越来越受到关注和重视。文中阐述了现阶段改善牛乳脂中共轭亚油酸含量的各种方法和手段,为以后共轭亚油酸的深入研究提供一些参考。     

日粮添加共轭亚油酸钙盐和葵花油对奶牛产奶性能及饲料消化率的影响

试验研究了奶牛日粮中添加过瘤胃共轭亚油酸(Ca-CLA),同时添加葵花油对奶牛生产性能和饲料利用率的影响。选择健康、泌乳月份与产奶量相近的多胎荷斯坦泌乳牛20头,随机分成5组,每组4头。对照组(A组)基础日粮为60%粗饲料(苜蓿、羊草、青贮)和40%精料(以DM为基础),处理组在对照组日粮基础上每天每头牛分别添加Ca-CLA100g(B组)、葵花油350g(C组)、Ca-CLA100g+葵花油350g(D组)、Ca-CLA50g+葵花油175g(E组)。试验共进行52d。结果表明:C组产奶量较对照组差异不显著(P>0.05),B、D、E组产奶量较对照组都分别显著提高2.20%、9.95%、11.16%(P<0.05);B、C、D、E组牛奶的乳脂率较对照组都分别显著降低15.00%、6.74%、21.74%、14.35%(P<0.05)。与对照组相比,B组显著提高饲料中EE、CP、NDF、ADF消化率;C组除脂肪外其它营养成分消化率有降低的趋势但差异不显著;D、E组除脂肪消化率显著提高外,其它营养成分消化率差异不显著。     

牛乳脂共轭亚油酸的合成及其营养调控

共轭亚油酸(CLA)是存在于动物脂肪和乳脂中的天然活性成分。本文综述了牛乳脂CLA的来源、合成机制及其营养调控。     

Concentrations of retinol and tocopherols in the milk of cows supplemented with conjugated linoleic acid

This study was performed to investigate the hypothesis that supplementation of conjugated linoleic acid (CLA) changes the concentrations of retinol and tocopherols in the milk of cows. To investigate this hypothesis, Holstein cows received daily from 3 weeks ante‐partum to 14 weeks post‐partum either 172 g of a CLA‐free rumen‐protected control fat (control group, n = 20) or the same amount of a rumen‐protected CLA fat, supplying 4.3 g of cis‐9, trans‐11 CLA and 3.8 g of trans‐10, cis‐12 CLA per d (CLA group, n = 20). Milk samples (collected at weeks 1, 3, 5, 8 and 11 of lactation) were analysed for retinol, α‐ and γ‐tocopherol concentrations. Milk of cows supplemented with CLA had higher concentrations of retinol (+34%), α‐tocopherol (+44%) and γ‐tocopherol (+21%) than milk of control cows (p < 0.05). The daily output of these vitamins via milk was also greater in cows of the CLA group than in cows of the control group (+36, 50 and 24% for retinol, α‐tocopherol and γ‐tocopherol, respectively, p < 0.05). In agreement with higher concentrations of tocopherols, concentrations of thiobarbituric acid‐reactive substances, determined in milk of week 5, were lower in cows of the CLA group than in control cows, indicative of a lower susceptibility of milk lipids to peroxidation. Plasma concentrations of retinol and α‐tocopherol, determined at 1 and 5 weeks post‐partum, were not different between the two groups of cows. In conclusion, this study shows that supplementing dairy cows with a moderate amount of CLA causes an increase of the concentrations of vitamins A and E in the milk and results in an increased output of those vitamins via milk. These effects might be beneficial with respect to the nutritional value of dairy products and the susceptibility of milk fat to oxidative deterioration.     

Effect of dietary fish oil on milk yield, fatty acids content and serum metabolic profile in dairy cows

The aim of the study was to evaluate the effects of dietary unprotected fish oil on milk yield, fatty acids content and serum metabolic profile in dairy cows. Forty lactating Polish Holstein-Friesian cows were assigned to two groups. The cows were fed a control basal diet (C group), or a basal diet containing 2% addition of fish oil on mineral carrier (FOM group) during a 8-week period. Supplementing FOM diet of dairy cows had no significant effect on milk fat, milk protein, milk lactose concentration and somatic cells count, but increased the milk yield (36.5 kg/d), (p < 0.05) compared with the control cows (34.28 kg/d). We observed an increase (p < 0.05) in body condition scoring between C and FOM groups. Additionally, higher levels of non-esterified fatty acids and β-hydroxybutyrate acid were noticed in FOM group after 8 weeks of the experiment; however, these serum parameters still were in the reference range. Concentration of insulin was higher (30.40 μU/ml; p < 0.01) in the FOM group compared with the control group (14.03 μU/ml). In the FOM group, significant increase (p < 0.01) in long-chain fatty acids, mainly cis-9, trans-11 CLA and n-3 fatty acids (eicosapentaenoic and docosahexaenoic acids) was observed. The obtained results demonstrated that addition of fish oil to cows' diet could profitably modify the fatty acids in cow's milk.