奶牛乳脂率降低的生物学机制

乳脂是最易受日粮影响的一种乳成分,而乳脂含量可以直接影响到乳制品的等级及其加工工艺。近年,有大量的研究证明乳脂率下降的原因是由于日粮因素改变了瘤胃pH值等发酵参数,使得合成乳脂的前体物供应不足或产生了抑制乳脂合成的中间产物所造成的。本文即是对奶牛乳脂率降低的的两种主要生物机制进行了讨论。     

奶牛乳脂合成及其影响因素

乳脂是一种高质量的天然脂肪,是牛乳的主要营养成分。乳脂率是衡量牛奶品质优劣的关键指标,同时也是制约中国奶业发展的重要因素。近年来,随着中国奶牛业的不断发展,奶牛的产奶量日益提高,但乳脂率却未见增长。通常情况下牛奶的乳脂率为3%~4%,产奶量与乳脂率之间呈相互制约关系,如何提高乳脂率一直是学者们研究的热点。为深入研究并解决这一问题,作者介绍了乳脂组成及合成机理,并从日粮、瘤胃微生物及遗传等方面分析了影响奶牛乳脂合成的因素。同时作者还对影响奶牛乳脂合成的重要功能基因（SREBPs、PPARs、CIDEC基因）及mTOR信号通路的作用进行了综述。乳脂合成是一个动态的、复杂的多网络调控的过程,需要大量的基因参与,研究各信号通路间的相互作用可为人工调控乳脂合成提供理论基础,也为日后泌乳生物学研究奠定理论基础。     

奶牛乳脂合成及其影响因素

乳脂是一种高质量的天然脂肪,是牛乳的主要营养成分。乳脂率是衡量牛奶品质优劣的关键指标,同时也是制约中国奶业发展的重要因素。近年来,随着中国奶牛业的不断发展,奶牛的产奶量日益提高,但乳脂率却未见增长。通常情况下牛奶的乳脂率为3%~4%,产奶量与乳脂率之间呈相互制约关系,如何提高乳脂率一直是学者们研究的热点。为深入研究并解决这一问题,作者介绍了乳脂组成及合成机理,并从日粮、瘤胃微生物及遗传等方面分析了影响奶牛乳脂合成的因素。同时作者还对影响奶牛乳脂合成的重要功能基因(SREBPs、PPARs、CIDEC基因)及mTOR信号通路的作用进行了综述。乳脂合成是一个动态的、复杂的多网络调控的过程,需要大量的基因参与,研究各信号通路间的相互作用可为人工调控乳脂合成提供理论基础,也为日后泌乳生物学研究奠定理论基础。     

反刍动物共轭亚油酸的合成及其对乳脂率的影响

共轭亚油酸(CLA)是一种主要存在于反刍动物脂肪和乳脂中的天然活性成分.亚油酸和亚麻酸能通过瘤胃微生物的一系列异构和脱氢作用合成CLA,反式油酸在反刍动物肝脏微粒体、乳腺细胞和脂肪组织中被△9-脱氢酶脱氢也能生成c9,t11-CLA,并被确认为反刍动物CLA的主要来源.反刍动物体内CLA的合成受动物品种、环境、日粮等多种因素影响,个体之间也存在差异.在日粮中添加不饱和脂肪酸提高CLA含量的同时,对乳脂率会造成较大的影响.本文综述了反刍动物CLA合成及饲喂不饱和脂肪酸对其乳脂率的影响.     

奶牛乳脂降低综合征发病机制研究进展

乳脂是牛奶中受日粮影响最大的成分。乳脂降低综合征的发病机制主要包括日粮因素造成乳脂合成前体物不足和瘤胃氢化异常产物抑制乳腺脂肪酸合成等。本文就乳脂降低综合征发病机制的研究进展进行综述,为充分认识和控制乳脂降低奠定理论基础。     

奶牛日粮中影响产奶量和乳脂率的因素

五、日粮脂肪含量 对奶成分影响最大的是由日粮脂肪和碳水化合物的结构引起,在正常范围内日粮的蛋白质不起作用。等能日粮增加脂肪可提高乳脂率。日粮的脂肪酸向乳脂的转化依赖于脂肪酸在日粮的含量,泌乳阶段和糖元营养的摄入影响乳脂率和脂肪组织的代谢平衡。     

瘤胃微生物在奶牛乳脂肪合成中的调节作用研究进展

乳脂肪不仅是牛乳的主要成分之一,同时乳脂肪含量也是评价牛乳质量的重要指标.乳脂肪的合成涉及到日粮营养物质通过奶牛机体转化为乳营养成分的复杂生物学过程,受日粮配方、遗传背景、生理状态、瘤胃微生物等多方面的影响.瘤胃微生物可以通过自身合成的酶类对日粮进行降解,进而对乳脂肪合成前体物质的生成和利用起到一定的调节作用,乳脂肪前...     

影响牛奶trans11C18∶1和CLA合成的因素

乳脂肪受日粮因素的调控的可塑性大，CLA是乳脂肪中的一种微量不饱和脂肪酸，影响乳脂肪的物理和生物学特性。CLA最初发现于奶牛瘤胃，但牛奶中CLA主要通过乳腺组织Δ9去饱和酶作用于trans11C18∶1而内源合成。研究结果表明，日粮因素、动物个体间的差异和动物组织间SCD酶活性的差异是影响乳脂CLA合成的关键因素。作者针对影响trans11C18∶1和Δ9去饱和酶的因素对CLA合成调控因素作了简要论述。     

影响牛奶trans11C18∶1和CLA合成的因素

 乳脂肪受日粮因素的调控的可塑性大，CLA是乳脂肪中的一种微量不饱和脂肪酸，影响乳脂肪的物理和生物学特性。CLA最初发现于奶牛瘤胃，但牛奶中CLA主要通过乳腺组织Δ9去饱和酶作用于trans11C18∶1而内源合成。研究结果表明，日粮因素、动物个体间的差异和动物组织间SCD酶活性的差异是影响乳脂CLA合成的关键因素。作者针对影响trans11C18∶1和Δ9去饱和酶的因素对CLA合成调控因素作了简要论述。     

反式脂肪酸降低乳脂合成的机理

乳中的反式脂肪酸直接来源于日粮脂肪或由瘤胃微生物氢化生成,本文重点介绍了反10-油酸和反10,顺12-共轭亚油酸两种不同反式脂肪酸对乳脂合成的影响,讨论了反式脂肪酸影响乳脂合成的机理,可能是反式脂肪酸通过抑制乳腺中脂肪酸合成的关键酶乙酰辅酶A羧化酶和脂肪酸合成酶的活性,进而导致乳脂合成的减少。     

Nutritional and somatotropin regulation of the mitogenic response of mammary cells to mammary tissue extracts

Our objective was to investigate the mitogenic response of primary mammary epithelial cells to extracts of mammary parenchyma from 24 prepubertal Friesian heifers treated with placebo or growth hormone at either a low or a high feeding level. The mitogenic responses to mammary extracts were tested by using primary mammary epithelial organoids obtained from prepubertal heifers cultured for 4 to 5 d in collagen gels in serum-free medium supplemented to 5% concentration of the mammary extracts. Cell proliferation was determined using [methyl-3H]thymidine incorporation as a measure of DNA synthesis. High feeding level reduced DNA synthesis in response to mammary extracts. At low feeding level, growth hormone treatment decreased DNA synthesis in response to mammary extracts whereas, at high feeding level, growth hormone increased DNA synthesis in response to mammary extracts. These results suggest that locally produced growth factors are involved in the regulation of mammary development when mammary growth is modulated by feeding level and growth hormone treatment.     

奶牛干奶期乳腺免疫力低下机理及影响因素分析

奶牛乳腺自身抵抗力下降是乳腺炎发生的直接原因,也是兽医产科学研究的重点,从提高奶牛自身抵抗力预防乳腺炎的发生已成近年来研究的新热点,作者着重就奶牛在泌乳周期中尤其是干奶期抵抗力下降的机理做了必要的分析和探讨,对影响干奶期免疫力低下的一些因素也作了详尽阐述,这些方面的论述对乳腺机能方面的进一步研究和预防乳腺炎的发生有一定的参考和应用价值。     

乳腺上皮细胞在乳腺炎症反应中的作用

乳腺上皮细胞的重要生理功能是合成和分泌乳汁中的主要营养成分。近年来乳腺上皮细胞作为先天性免疫的重要组成部分,其在预防和治疗乳腺炎中的作用受到人们的广泛关注。通过乳腺上皮细胞原代培养物和乳腺上皮细胞系对乳腺分泌的免疫活性物质进行研究,结果表明,乳腺上皮细胞在病原微生物侵入乳腺时,能分泌众多的免疫调节因子（如炎症趋化因子、前炎性细胞因子和宿主防御肽等）,这些免疫活性成分对乳腺炎的发生与病程发展起重要作用。      

Ultrasonographic assessment of the feline mammary gland

The aim of this study is to characterise the feline mammary echotexture using B-mode ultrasonography, which is not routinely used to examine the feline mammary gland. Using a 5-9 MHz linear transducer the ultrasonographic appearance of non-stimulated and stimulated mammary glands was determined in 35 mature intact non-pregnant, pregnant and lactating queens aged from 16 months to 8 years. In intact non-pregnant queens, mammary glands are fairly underdeveloped and on the ultrasonograms they appear with a regular hypoechoic texture and generally show a thickness of less than 2.0mm. The stimulated mammary tissue typically presents a more hyperechoic appearance compared to the non-stimulated gland and a fine granular echotexture. Maximum echogenicity of the mammary gland is reached during lactation. In late pregnancy, the mammary glands reach 6-9 mm in thickness. During lactation, the size of the glands depends on the existence of a suckling stimulus, with the suckled glands reaching about 11 mm in thickness. Ductal structures can only be imaged during late pregnancy and lactation. Ultrasonographic evaluation of the feline mammary gland can become a valuable diagnostic tool to characterise physiological changes and may further contribute to a better characterisation of diseased mammary tissue.     

动物乳腺干细胞研究进展

乳腺是一个高度活跃的器官,在青春期和生殖周期中,其上皮细胞发生了极大的变化。这些变化是由专门的干细胞和祖细胞推动的。研究乳腺干细胞对动物乳腺发育、哺乳和乳腺癌等方面都有着重大意义。如今,在乳腺干细胞生物学研究方面已经取得了显著进步。乳腺干细胞是组织学上未分化的上皮细胞,可以对称分裂产生两个相同的干细胞,或不对称地产生一个干细胞和一个腔上皮祖细胞或基底/肌上皮祖细胞。通过标记滞留细胞、染料排斥法、干细胞抗原-1标记、细胞表面标记物标记以及谱系示踪等方法可以鉴定出多种不同类型的乳腺干/祖细胞,应用多种不同方法分离鉴定乳腺干细胞有助于深入了解其异质性。乳腺的研究主要分为6个阶段：胚胎期、青春期、性成熟期、妊娠期、泌乳期和退化期。在乳腺不同发育阶段,乳腺干/祖细胞的类型及特性不同。有研究表明,在胚胎期就有基底和管腔谱系的祖细胞产生,静止的乳腺干细胞也可能来自于胚胎期,出生后,静止干细胞可以在卵巢激素的刺激作用下重新进入细胞周期,产生乳腺细胞谱系和自我更新。作者介绍了乳腺干细胞和祖细胞的存在、形态特征、鉴定方法,简述了乳腺干细胞在胚胎期、青春期和妊娠期的特征,分析了目前该领域研究的不足之处以及对未来应用的展望。     

乳腺中脂肪细胞的转化和更迭

雌性动物的乳腺组织是由胚胎时期的外胚层发育而来,出生时只有少量导管和皮下基质结构,而后在性成熟、妊娠和泌乳期乳腺发育达到峰值,这一特点使乳腺成为出生后唯一可以重复再生的器官。在乳腺发育到退化的循环中,乳腺的上皮细胞、基质白色脂肪细胞、棕色脂肪细胞和肌上皮细胞经历了一系列转化和更迭,脂肪细胞的动态转化反映了乳腺的功能变化。研究乳腺细胞的转化和更迭与母畜的泌乳直接相关,对延续母畜的生产效率有重要意义。本文就乳腺中脂肪细胞转化方面的最新研究进展进行综述,为深度揭示乳腺发育过程中细胞更迭的机制提供前沿研究信息。     

Immunity in the mammary gland.

The ruminant mammary gland is an extremely important economic organ in that it provides a major nutrition source for a significant portion of the world's human population. The ruminant mammary gland is also responsible for providing protective immunity to neonates and for defending itself from invading pathogens. A wide array of humoral and cellular immune mechanisms are present in the mammary gland and actively participate in providing immunity to newborns and the mammary gland per se. The acute inflammatory response is essential in determining the outcome of intramammary challenge, and factors affecting innate and adaptive immunity in the context of mammary health are reviewed in detail. The ruminant mammary gland is also unique in that lymphocyte trafficking, which is essential to adaptive immunity, is shared with the peripheral immune system rather than the common mucosal immune system.     

Research Progress on the Development of Mammary Glands

Mammary gland is a kind of exocrine glands and a dynamic organ.Structure of mammary gland changes throughout the female reproductive cycles.Development of mammary gland occurs in the defined stages that are closely linted to sexual development and reproduction, namely embryonic, prepubertal and pubertal stages, pregnancy, lactation and involution.In this review, the roles of epithelial-stromal (mesenchymal) interactions in embryonic and postnatal mammary development were summarized, elaborated the regulations of different kinds of hormones on the mammary development after pubertal stage, and described the discovery of mammary stem cell populations (MaSC) and selection markers of mice and human.The objective of this work was to learn the basic processes and potential regulation mechanisms of the mammary development to provide some help for the researchers in the field of mammary gland.     

Expression of potential lymphocyte trafficking mediator molecules in the mammary gland

The mammary gland performs a variety of immunological functions, including protecting itself from mastitis and protecting neonates from infectious agents. Several molecules that mediate lymphocyte trafficking in the immune system are also expressed in the mammary gland. This review is focused on the immunological function of these molecules, especially glycosylation-dependent cell adhesion molecule-1 (GlyCAM-1) and mucosal addressin cell adhesion molecule-1 (MAdCAM-1) in the mammary gland. GlyCAM-1 is expressed in the lactating mouse mammary gland. Endothelial cells produce this protein and secrete it into milk. The glycosylated modification of mammary gland GlyCAM-1 is different from that of the lymph nodes, and lacks the binding ability for L-selectin on lymphocytes. GlyCAM-1 in the mammary gland is not involved in lymphocyte migration, and probably has another function besides that of the lymph nodes. MAdCAM-1 is expressed on endothelial cells of small venules around mouse mammary lobules during lactation. This molecule has the ability to interact with alpha4beta7 integrin on lymphocytes and mediates lymphocyte recruitment to the mammary gland. The density of beta7+/CD3+ T-cells is correlated with the density of the MAdCAM-1-stained area, suggesting that MAdCAM-1 may mediate the migration of these cells. In contrast, there is no relationship between MAdCAM-1 expression and the number of beta7+/c-IgA+ B-cells, implying that some other factor is involved in lymphocyte migration to the mammary gland. Chemokines, such as IL-8, GRO-alpha, MCP-1, RANTES and MEC, have been detected in human and mouse mammary glands. Although little information is available, these molecules may contribute to lymphocyte migration to the mammary gland.