牛奶被誉为最接近完美的食物，可提供一系列对人类健康有益的营养素，包括脂质、蛋白质、生物活性肽、矿物质、维生素等[1]。随着营养学研究的不断深入，人们逐渐认识到乳脂对人类健康的积极影响，研究发现，全脂乳制品的摄入量与高血压、糖尿病等代谢综合征患病风险呈负相关关系[2]。脂肪酸是乳脂发挥营养功能的主要活性因子，某些生物活性脂肪酸，如C4 ∶ 0等短链脂肪酸(SCFA)，C15 ∶ 0等奇数链脂肪酸(OCFA)，C15 ∶ 0-iso、C15 ∶ 0-anteiso等支链脂肪酸(BCFA)，C18 ∶ 1-c9、C18 ∶ 1-t11等单不饱和脂肪酸(MUFA)，C18 ∶ 3-c9, 12, 15(α-亚麻酸，ALA)、C20 ∶ 5-c5, 8, 11, 14, 17(二十碳五烯酸，EPA)、C22 ∶ 6-c4, 7, 10, 13, 16, 19(二十二碳六烯酸，DHA)等ω-3多不饱和脂肪酸(ω-3 PUFA)，C18 ∶ 2-c9, t11等共轭亚油酸(CLA)，对预防心血管疾病、促进中枢神经系统发育、缓解炎症和提高免疫功能等具有积极影响[3-7]。除此之外，乳脂等反刍动物源性脂质是人类膳食中丁酸、CLA、BCFA等的主要来源，该类脂肪酸在植物源性脂质、单胃动物源性脂质几乎不存在。然而，牛奶中脂肪酸组成和含量易受遗传、泌乳阶段、胎次、季节等非营养因素和饲粮等营养因素的影响。本文主要综述了牛奶中脂肪酸的合成机理以及影响牛奶中脂肪酸组成和含量的因素，为牛奶中脂肪酸调控提供理论依据。
1 牛奶中脂肪酸的种类牛奶中脂肪酸以结合态和游离态2种形式存在，绝大部分脂肪酸以结合态存在，少于0.5%的脂肪酸以游离态(游离脂肪酸)存在，其中，结合态脂肪酸包括约95%的甘油三酯、约2%的甘油二酯、约1%的单酰甘油、约1%的磷脂、少于0.5%的胆固醇[8-9]。研究发现，牛奶中含有400多种脂肪酸，包括饱和脂肪酸(SFA)、含碳碳双键的不饱和脂肪酸(UFA)、羟基脂肪酸、环烷基脂肪酸和氧代脂肪酸等[10-12]。不同学者报道的牛奶中含量最高的脂肪酸有所差异，研究结果普遍表明，牛奶中约14种脂肪酸含量超过1%，分别是C4 ∶ 0、C6 ∶ 0、C8 ∶ 0、C10 ∶ 0、C12 ∶ 0、C14 ∶ 0、C14 ∶ 1-c9、C15 ∶ 0、C16 ∶ 0、C16 ∶ 1-c9、C18 ∶ 0、C18 ∶ 1-c9、C18 ∶ 1-t11和C18 ∶ 2-c9, c12；其中，C16 ∶ 0或C18 ∶ 1-c9是牛奶中含量最高的脂肪酸，占总脂肪酸含量的15%~30%[13-15]。本文主要探讨了SFA和UFA，其种类及含量见表 1。
2 牛奶中脂肪酸的合成
反刍动物摄入饲粮后，饲粮中的纤维素等碳水化合物在瘤胃中发酵形成乙酸、丙酸、丁酸、异丁酸、戊酸和异戊酸等挥发性脂肪酸，其中乙酸和丁酸主要被瘤胃上皮细胞吸收转化为乙酸和β-羟基丁酸，经血液循环转运至乳腺参与脂肪酸从头合成；瘤胃微生物利用丙酸和戊酸或对自身脂肪酸进行α-氧化反应形成OCFA，利用异丁酸和异戊酸合成BCFA，奇数链和支链脂肪酸(OBCFA)主要以细菌膜脂的形成存在瘤胃细菌内，瘤胃细菌随固体食糜经过网胃、瓣胃、皱胃到达小肠，被胆汁、胰脂肪酶等消化酶分解形成OBCFA[18]。饲粮中的脂质在瘤胃微生物脂解酶的作用下分解形成游离脂肪酸，绝大部分UFA经瘤胃微生物的生物氢化作用形成SFA，SFA和UFA被转运至小肠，与OBCFA共同构成脂蛋白，经小肠上皮细胞吸收进入血液循环，随即进入肝脏、脂肪组织、乳腺等发生脂肪酸代谢[19-20]。脂肪酸在肝脏中发生去饱和、碳链延长等作用形成长链UFA异构体，并以脂蛋白和游离脂肪酸的形式释放到血液中[21]。当机体处于能量负平衡时，机体动员脂质分解形成以C18 ∶ 1-c9为主的游离脂肪酸释放到血液中[22]。
乳腺上皮细胞利用乙酸和β-羟基丁酸从头合成小于C16的脂肪酸和约50%的C16，通过直接从血液中摄取游离脂肪酸得到大于C16的脂肪酸和约50%的C16[23]。其中，牛奶中几乎所有的SCFA、中链脂肪酸(MCFA)来源于脂肪酸从头合成，少部分长链脂肪酸(LCFA)经脂肪酸从头合成，绝大部分LCFA来源于血液。此外，乳腺Δ9-去饱和酶会催化脂肪酸转化成UFA[24-25]。经从头合成的、从血液中摄取的以及去饱和等过程形成的SFA和UFA，以甘油酯、磷脂、胆固醇酯、游离脂肪酸等形式存在乳脂中。乳腺从头合成的脂肪酸以C16 SFA为主，而反刍动物采食植物性饲料的脂质以C18为主，摄入C18 UFA经瘤胃的生物氢化和乳腺Δ9-去饱和酶的去饱和形成大量的C18 ∶ 1-c9[26]。因此，C16 ∶ 0或C18 ∶ 1-c9是乳脂中含量最高的2种脂肪酸。
脂肪酸从饲粮到牛奶的合成过程中，瘤胃、肝脏和乳腺等发挥了至关重要的作用。脂肪酸在反刍动物体内的代谢途径见图 1。
3 影响牛奶中脂肪酸组成和含量的因素
牛奶中脂肪酸组成和含量受遗传、泌乳阶段、胎次、季节等非营养性因素和饲粮等营养因素的影响。研究表明，遗传因素是影响牛奶SFA组成和含量的主要因素，饲粮是影响牛奶UFA组成和含量的主要因素。
3.1 非营养因素 3.1.1 遗传因素乳脂中从头合成的脂肪酸相比来源于饲粮和体脂动员的脂肪酸受到更多的遗传调控[25, 28-30]。研究发现，牛奶中脂肪酸具有一定的遗传变异性，C4 ∶ 0~C16 ∶ 0等从头合成的脂肪酸的遗传变异较高，遗传力为0.31~0.54，C18 UFA等饲粮和体脂动员的脂肪酸的遗传变异中等，遗传力为0.09~0.21，C18 ∶ 1-t11和C18 ∶ 2-c9, t11的遗传力分别为0.12和0.21[31]。荷斯坦奶牛乳脂中MCFA的平均遗传力(0.32)高于SCFA(0.24)和LCFA(0.23)，SFA的平均遗传力(0.33)大于UFA(0.21)[30]。脂肪酸之间，尤其是来源相似的脂肪酸之间有较强的正遗传相关性，乳腺从头合成的脂肪酸(C6 ∶ 0、C8 ∶ 0、C10 ∶ 0、C12 ∶ 0和C14 ∶ 0)彼此之间显示出较强的正遗传相关性，SFA与UFA呈较强的遗传负相关[32]。中等及较高遗传变异的性状能通过遗传选择予以调控。因此，通过遗传选择能改善牛奶中脂肪酸组成，但改善特定的脂肪酸会影响牛奶整个脂肪酸的组成和含量[25]。
3.1.2 泌乳期奶牛的泌乳期通常分为3个阶段：泌乳初期(产后1~100 d)、泌乳中期(产后101~200 d)和泌乳后期(产后200 d以上)。处于不同泌乳阶段奶牛的能量平衡不同，肝脏、脂肪组织、乳腺等脂肪酸代谢活动发生改变，造成了牛奶中脂肪酸组成的差异[33]。泌乳初期，尤其是泌乳的最初几天，奶牛处于能量负平衡状态，机体动员身体储备将有限的营养物质用于乳汁合成，增加体脂分解，释放以C18 ∶ 1-c9等LCFA为主的游离脂肪酸用于乳腺或肝脏的代谢[34]。血液中游离脂肪酸含量的升高增加了乳腺对LCFA的摄取，抑制乙酰辅酶A羧化酶的活性，从而影响脂肪酸的从头合成[35]。随着泌乳过程中能量平衡的改善或饲粮摄入量的增加，泌乳21周左右，奶牛已经从能量负平衡状态逐渐转变为能量平衡状态，乳腺上皮细胞的活性和代谢功能充分发挥，牛奶中脂肪酸组成趋于稳定[36]。因此，SCFA和MCFA等来源于从头合成的脂肪酸含量在泌乳初期比例较低，随着泌乳期延长，其含量显著增加，在泌乳后期达到最高；LCFA含量在泌乳初期比例较高，随着泌乳期延长，其含量显著降低，在泌乳后期达到最低[37-38]。但丁酸可以由2条独立于乙酰辅酶A羧化酶途径产生，并且其合成可能不会被游离脂肪酸含量增加所抑制，所以丁酸与泌乳阶段对SCFA含量的变化规律不同，丁酸含量随泌乳期延长显著降低[39]。
作为牛奶中脂肪酸中占比较大的2种脂肪酸，C16 ∶ 0和C18 ∶ 1-c9因脂肪酸合成途径不同，在泌乳阶段表现出不同变化规律。C16 ∶ 0来源于脂肪酸从头合成和血液摄取2部分，而C18 ∶ 1-c9仅来源于血液摄取，从整个泌乳阶段来看，C16 ∶ 0含量在泌乳开始时最低，而C18 ∶ 1-c9含量在泌乳最初几天最高，随泌乳期延长，奶牛能量平衡改善，体脂分解释放游离脂肪酸作用减弱，C16 ∶ 0含量显著增加，而C18 ∶ 1-c9含量显著降低[40]。研究发现，与泌乳第1周相比，至泌乳第21周，C16 ∶ 0含量增加了25.93%，C18 ∶ 1-c9含量降低了40.58%[37]。Kay等[41]研究饲喂相同饲粮的奶牛在泌乳初期内乳脂肪酸组成变化，发现从泌乳第1周至第16周，牛奶中C18 ∶ 1-t11和C18 ∶ 2-c9, t11含量分别增加了31%和76%，而C18 ∶ 0含量降低了19.5%，推测C18 ∶ 0含量下降而C18 ∶ 1-t11含量增加可能是饲粮摄入量增加或瘤胃通过率增加导致更多PUFA在瘤胃内不完全生物氢化所致；C18 ∶ 2-c9, t11含量增加是因为其内源性合成的前体物C18 ∶ 1-t11含量增加[42-43]。
3.1.3 胎次初产奶牛乳脂中PUFA含量较高，SFA含量较低，而2胎及以上的奶牛乳脂中SFA含量较高，UFA含量较低[44-45]。Craninx等[46]研究发现，与经产奶牛相比，初产奶牛乳脂中C16 ∶ 0含量显著降低，而C18 ∶ 0、C18 ∶ 1-c9、C18 ∶ 1-t11和C18 ∶ 2-c9, t11含量显著升高。初产和经产奶牛牛奶中脂肪酸的变化可能与乳脂合成相关酶的活性不同有关[47]。初产奶牛在泌乳早期乳腺中参与脂肪酸生物合成的脂肪酸合成酶活性较低，随泌乳天数的增加，脂肪酸合成酶活性逐渐升高，而经产动物泌乳早期的脂肪酸合成酶活性与初产奶牛泌乳末期相同[48]。
3.1.4 季节季节对牛奶中脂肪酸组成和含量的影响归因于奶牛饲粮结构的改变。冬季奶牛摄入的粗饲料以干草、青贮为主，而春夏季奶牛可通过放牧摄入更多的新鲜牧草。奶牛采食新鲜牧草导致C18 ∶ 2和C18 ∶ 3等PUFA摄入量增加，C18等PUFA摄入量的增加不仅在一定程度上抑制乳腺中脂肪酸的从头合成，从而降低牛奶中SFA含量，而且增加瘤胃生物氢化成C18 ∶ 0、C18 ∶ 1-t11的含量，提高Δ9-去饱和酶催化合成C18 ∶ 1-c9、C18 ∶ 2-c9, t11的底物含量，从而提高牛奶中MUFA含量[49]。研究发现，夏季牛奶中SFA和UFA的总含量显著低于冬季，但牛奶中MUFA的总含量显著高于冬季[50-51]。与冬季相比，春夏季奶牛乳脂中C18 ∶ 0、C18 ∶ 1-c9、C18 ∶ 1-t11、C18 ∶ 2-c9, t11、C18 ∶ 3-c9, 12, 15含量显著升高[52-53]。
3.2 营养因素 3.2.1 粗饲料类型粗饲料是奶牛重要的养分来源，占奶牛饲粮的50%~90%。研究发现，粗饲料类型能显著影响牛奶中脂肪酸的组成和含量。玉米青贮是奶牛主要的粗饲料，饲喂玉米青贮的奶牛乳脂中C16 ∶ 0含量最高(33.6%)，UFA含量较低(32.5%)[54]。研究发现，不同水平的豆科牧草与玉米青贮混合青贮饲喂奶牛能降低乳脂中SFA含量，提高UFA含量。使用全株大豆青贮部分替代玉米青贮可以显著提高UFA/SFA至0.505。使用苜蓿青贮部分代替玉米青贮，显著提高乳脂中C18 ∶ 1-c9、ALA含量，降低乳脂中ω-6/ω-3 PUFA至3.77[55]。红三叶青贮逐渐替代玉米青贮导致乳脂中PUFA含量显著增加，C18 ∶ 1-c9含量显著升高，ALA含量线性增加，ω-6/ω-3 PUFA显著降低，C18 ∶ 1-t11、LA、C18 ∶ 2-c9, t11含量显著降低，C14 ∶ 0含量线性减少，C18 ∶ 0含量保持恒定，C16 ∶ 0含量保持恒定，BCFA含量保持恒定[56]。此外，研究发现红三叶草青贮逐渐代替禾本科牧草青贮可以线性降低乳脂中C4 ∶ 0~C8 ∶ 0、C14 ∶ 0和C16 ∶ 0含量，并线性增加LA和ALA含量[57]，增大瓣胃中ALA流量，降低了瘤胃中ALA的生物氢化[16]。多年生黑麦草-白三叶草中LA、ALA含量显著高于菊苣或车前草等饲用草本植物，但与多年生黑麦草-白三叶草相比，饲喂菊苣或车前草奶牛的乳脂中C18 ∶ 1-c9、C18 ∶ 2-c9, t11含量显著降低，LA、ALA含量显著升高，LA从牧草到牛奶的表观转移率从饲喂多年生黑麦草-白三叶草的7.8%增加到车前草和菊苣的10.5%和10.3%，而ALA的转移率从1.6%分别增加到2.9%和3.6%，可能是由于饲用草本植物中的UFA在奶牛体内的生物氢化作用更少，牛奶中UFA含量更高[58-59]。在黑麦草-红三叶青贮饲料中添加车前草，显著提高了奶牛乳脂中PUFA、C18 ∶ 1-t11和C18 ∶ 2-c9, t11含量，降低ω-6/ω-3PUFA至1.5 ∶ 1.0[60]。
综上所述，豆科牧草和饲用草本植物较禾本科牧草能显著提高牛奶中UFA含量。饲料种类对牛奶中脂肪酸组成的影响不能简单用脂肪酸摄入量的差异来解释，可能是饲草中存在某种特定的代谢物抑制脂肪酶的活性导致瘤胃中脂肪分解减少，过瘤胃UFA含量增加，或是影响了瘤胃细菌的丰度，限制了饲料与瘤胃细菌的结合，降低了瘤胃生物氢化速率，从而提高了UFA从饲粮到牛奶的转移率，最终影响牛奶中脂肪酸的组成和含量，需要进一步试验探究饲粮影响牛奶中脂肪酸组成和含量的具体生物学机制。
3.2.2 脂质改善剂研究表明，饲粮中添加油料籽实、油脂、藻类等脂质改善剂改变牛奶中脂肪酸组成，可提高乳中PUFA含量[61-63]。然而，油菜籽、葵花籽、亚麻籽中脂肪酸的组成存在较大差异，油菜籽中以C18 ∶ 1-c9为主，约占脂肪酸总含量的60%；葵花籽中以LA为主，约占54.6%；亚麻籽中以ALA为主，约占52.9%[64]。饲粮中添加油菜籽、亚麻籽等油料籽实显著提高乳脂中总MUFA、C18 ∶ 1-t11、C18 ∶ 1-c9、C18 ∶ 2-c9, t11含量，降低总SFA和某些SFA的含量；其中，亚麻籽对牛奶中脂肪酸的改善效果优于油菜籽，能提高ALA等ω-3 PUFA含量[65]。此外，对亚麻籽进行机械加工处理，能使乳脂中SFA和UFA含量发生显著变化，ALA、ω-3 PUFA、C18脂肪酸含量显著增加，LA、ω-6 PUFA、OCFA、C16脂肪酸含量显著下降[66]。饲粮中添加菜籽油、葵花籽油、亚麻籽油等植物油脂可显著降低牛奶中SCFA、OBCFA、C18 ∶ 0、LA、ALA含量[67]。其中，亚麻籽油能更大程度提高乳脂中LA含量[68]。一项荟萃分析表明，与亚麻籽油、整粒亚麻籽相比，经过机械加工的亚麻籽如粉碎亚麻籽饲喂奶牛，其乳脂中ALA含量显著升高[69]。饲粮中添加鱼油等动物油脂能显著提高乳脂中EPA、DHA含量，显著降低C4 ∶ 0~C18 ∶ 0 SFA含量，显著增加CLA、反式脂肪酸、PUFA含量[17]。饲粮中添加裂殖壶藻等藻类植物，能提高乳脂中DHA含量，但DHA从饲粮转移到牛奶中的效率很低，乳脂中SFA含量降低，而PUFA含量升高；乳脂中C18 ∶ 0、C18 ∶ 1-c9、LA和ALA含量降低，C18 ∶ 2-c9, t11、C18 ∶ 1-t9和C18 ∶ 1-t11含量升高[70]。
Ferlay等[68]研究发现，粗饲料类型与脂质补充剂对乳脂脂肪酸产量存在交互作用，饲喂干草和葵花籽油的奶牛乳脂中LA含量显著高于饲喂玉米青贮和葵花籽油的奶牛，饲喂干草和亚麻籽油的奶牛乳脂中ALA含量显著高于饲喂玉米青贮和亚麻籽油的奶牛，表明低SFA含量、高ALA含量的干草-亚麻籽饲粮可以提高牛奶PUFA含量，改善牛奶营养品质。
综上所述，油料籽实、油脂、藻类等脂质改善剂主要通过改变奶牛脂肪酸摄入量从而改善牛奶中脂肪酸组成，提高富含ω-3 PUFA的亚麻籽(油)、鱼油、裂殖壶藻等在饲粮中的添加比例能提高牛奶中PUFA含量。
3.2.3 饲养模式目前，牛奶集约化生产依赖于2种饲养模式：全年舍饲和季节性放牧与舍饲相结合。研究表明，放牧饲养有助于改善奶牛乳脂肪酸组成，放牧奶牛乳脂中SFA含量显著低于舍饲奶牛，MUFA、CLA、ALA、OBCFA含量显著高于舍饲奶牛[71]。放牧奶牛与舍饲奶牛乳脂脂肪酸组成差异主要归因于采食饲料的不同。舍饲奶牛采食以玉米、禾本科、豆科牧草、禾豆青贮或上述青贮饲料组合为主，辅以精料的全混合日粮；而放牧奶牛采食的新鲜牧草中含有更多的UFA，可以减低瘤胃生物氢化，影响Δ9-去饱和酶活性，影响乳腺对LCFA的摄取，从而提高乳脂中UFA含量[52, 72]。
4 小结牛奶中脂肪酸来源于脂肪酸从头合成、饲粮脂肪酸、体脂动员等，受遗传、泌乳期、胎次、季节、饲粮、饲养模式等诸多因素的影响，其中遗传和饲粮对牛奶中脂肪酸组成影响较大。在实际生产过程中，要充分利用饲粮等营养因素、脂肪酸遗传力和遗传相关性等遗传参数以及硬脂酰辅酶A去饱和酶等关键酶的多态性，以达到改善牛奶中脂肪酸组成和含量的目的。此外，有必要挖掘更多促进脂肪酸向长链PUFA延长、去饱和的酶和基因，通过调控酶的活性或基因表达，以生产富含ω-3 PUFA等生物活性脂肪酸的牛奶。
| [1] |
张养东, 刘月娟, 王宗伟, 等. 牛奶人类最接近完美的食物[J]. 中国乳业, 2017(6): 18-20. ZHANG Y D, LIU Y J, WANG Z W, et al. Milk is the closest to perfect food for human[J]. China Dairy, 2017(6): 18-20 (in Chinese). |
| [2] |
BHAVADHARINI B, DEHGHAN M, MENTE A, et al. Association of dairyconsumption withmetabolic syndrome, hypertension and diabetes in 147812 individuals from 21 countries[J]. Bmj Open Diabetes Research & Care, 2020, 8(1): 1-37. |
| [3] |
GÓMEZ-CORTÉS P, JUÁREZ M, DELAFUENTE M A. Milk fatty acids and potential health benefits: an updated vision[J]. Trends in Food Science & Technology, 2018, 81: 1-9. |
| [4] |
HANUS O, SAMKOVA E, KRIZOVA L, et al. Role of fatty acids in milk fat and the influence of selected factors on their variability-a review[J]. Molecules, 2018, 23(7): 1636. DOI:10.3390/molecules23071636 |
| [5] |
THORNING T K, RABEN A, THOLSTRUP T, et al. Milk and dairy products: good or bad for human health? An assessment of the totality of scientific evidence[J]. Food Nutrition Research, 2016, 60: 32527. DOI:10.3402/fnr.v60.32527 |
| [6] |
CALDER P C. Functional roles of fatty acids and their effects on human health[J]. Journal of Parenteral and Enteral Nutrition, 2015, 39: 18S-32S. DOI:10.1177/0148607115595980 |
| [7] |
GAO Y N, DAVIS B, ZHU W S, et al. Short chain fatty acid butyrate, a breast milk metabolite, enhances immature intestinal barrier function genes in response to inflammation in vitro and in vivo[J]. American Journalof Physiology-Gastrointestinal Liver Physiology, 2020. DOI:10.1152/ajpgi.00279 |
| [8] |
BRONDZ I. Development of fatty acid analysis by high-performance liquid chromatography, gaschromatography, and related techniques[J]. Analytica Chimica Acta, 2002, 465(1/2): 1-37. |
| [9] |
HAUG A, HOSTMARK AT, HARSTAD O M. Bovine milk in human nutrition-a review[J]. Lipids in Health Disease, 2007(6): 25. |
| [10] |
CALIGIANI A, MARSEGLIA A, PALLA G. An overview on the presence of cyclopropane fatty acids in milk and dairy products[J]. Journal of Agricultural and Food Chemistry, 2014, 62(31): 7828-7832. DOI:10.1021/jf4057204 |
| [11] |
KOKOTOU M G, MANTZOURANI C, BOURBOULA A, et al. A liquid chromatography high resolution mass spectrometry (LC-HRMS) method for the determinationof free hydroxy fatty acids in cow and goat milk[J]. Molecules, 2020, 25(17): 3947. DOI:10.3390/molecules25173947 |
| [12] |
JENSEN R G. The composition of bovine milk lipids-January 1995 to December 2000[J]. Journal of Dairy Science, 2002, 85(2): 295-350. DOI:10.3168/jds.S0022-0302(02)74079-4 |
| [13] |
李磊, 王昆, 何静, 等. 驼、牛、羊乳中脂肪酸含量的比较分析[J]. 食品科学, 2020, 40(6): 223-227. LI L, WANG K, HE J, et al. A comparative analysis of fatty acid profiles of camel, bovine and caprine milk[J]. Food Science, 2020, 40(6): 223-227 (in Chinese). |
| [14] |
TENG F, WANG P, YANG L, et al. Quantification of fatty acids in human, cow, buffalo, goat, yak, and camel milk using an improved one-step GC-FID method[J]. Food Analytical Methods, 2017, 10(8): 2881-2891. DOI:10.1007/s12161-017-0852-z |
| [15] |
DREIUCKER J, VETTER W. Fatty acids patterns in camel, moose, cow and human milk as determined with GC/MS after silver ion solid phase extraction[J]. Food Chemistry, 2011, 126(2): 762-771. DOI:10.1016/j.foodchem.2010.11.061 |
| [16] |
JAAKAMO M J, LUUKKONEN T J, KAIRENIUS P K, et al. The effect of dietary forage to concentrate ratio and forage type on milk fatty acid composition and milk fat globule size of lactating cows[J]. Journal of Dairy Science, 2019, 102(10): 8825-8838. DOI:10.3168/jds.2018-15833 |
| [17] |
KAIRENIUS P, ÄRÖLÄ A, LESKINEN H, et al. Dietary fish oil supplements depress milk fat yield and alter milk fatty acid composition in lactating cows fed grass silage-based diets[J]. Journal of Dairy Science, 2015, 98(8): 5653-5671. DOI:10.3168/jds.2015-9548 |
| [18] |
BUITENHUIS B, LASSEN J, NOEL S J, et al. Impact of the rumen microbiome on milk fatty acid composition of Holstein cattle[J]. Genetics Selection Evolution, 2019, 51(1): 23. DOI:10.1186/s12711-019-0464-8 |
| [19] |
DEWANCKELE L, TORAL P G, VLAEMINCK B, et al. Invited review: role of rumen biohydrogenation intermediates and rumen microbes in diet-induced milk fat depression: an update[J]. Journal of Dairy Science, 2020, 103(9): 7655-7681. DOI:10.3168/jds.2019-17662 |
| [20] |
NGUYEN Q V, MALAU-ADULI B S, CAVALIERI J, et al. Enhancing omega-3 longchain polyunsaturated fatty acid content of dairy-derived foods for human consumption[J]. Nutrients, 2019, 11(4): 743. DOI:10.3390/nu11040743 |
| [21] |
LANIER J S, CORL B A. Challenges in enriching milk fat with polyunsaturated fattyacids[J]. Journal of Animal Science and Biotechnology, 2015, 6(1): 26. DOI:10.1186/s40104-015-0025-0 |
| [22] |
LOFTEN J R, LINN J G, DRACKLEY J K, et al. Invited review: palmitic and stearicacid metabolism in lactating dairy cows[J]. Journal of Dairy Science, 2014, 97(8): 4661-4674. DOI:10.3168/jds.2014-7919 |
| [23] |
HARVATINE K J, BOISCLAIR Y R, BAUMAN D E. Recent advances in the regulation of milk fat synthesis[J]. Animal, 2009, 3(1): 40-54. DOI:10.1017/S1751731108003133 |
| [24] |
PETRINI J, IUNG L H S, RODRIGUEZ M A P, et al. Genetic parameters for milk fatty acids, milk yield and quality traits of a Holstein cattle population reared under tropical conditions[J]. Journal of Animal Breeding and Genetics, 2016, 133(5): 384-395. DOI:10.1111/jbg.12205 |
| [25] |
BASTIN C, GENGLER N, SOYEURT H. Phenotypic and genetic variability of production traits and milk fatty acid contents across days in milk for Walloon Holstein first-parity cows[J]. Journal of Dairy Science, 2011, 94(8): 4152-4163. DOI:10.3168/jds.2010-4108 |
| [26] |
VLAEMINCK B, FIEVEZ V, CABRITA A R J, et al. Factors affecting odd- and branched chain fatty acids in milk: a review[J]. Animal Feed Science and technology, 2006, 131(3/4): 389-417. |
| [27] |
王加启, 赵圣国, 郑楠, 等. 乳成分前体物生成与利用的调控网络[M]. 北京: 中国农业出版社, 2019. WANG J Q, ZHAO S G, ZHENG N, et al. Regulatory networks for the production and utilization of milk component precursors[M]. Beijing: China Agriculture Press, 2019 (in Chinese). |
| [28] |
HEIN L, SORENSEN L P, KARGO M, et al. Genetic analysis of predicted fatty acid profiles of milk from Danish Holstein and Danish Jersey cattle populations[J]. Journal of Dairy Science, 2018, 101(3): 2148-2157. DOI:10.3168/jds.2017-13225 |
| [29] |
VANROBAYS M L, BASTIN C, VANDENPLAS J, et al. Changes throughout lactation in phenotypic and genetic correlations between methane emissions and milk fatty acid contents predicted from milk mid-infrared spectra[J]. Journal of Dairy Science, 2016, 99(9): 7247-7260. DOI:10.3168/jds.2015-10646 |
| [30] |
NARAYANA S G, SCHENKEL F S, FLEMING A, et al. Genetic analysis of groups of mid infrared predicted fatty acids in milk[J]. Journal of Dairy Science, 2017, 100(6): 4731-4744. DOI:10.3168/jds.2016-12244 |
| [31] |
STOOP W M, VAN ARENDONK J A M, HECK J M L, et al. Genetic parameters for major milk fatty acids and milk production traits of dutch Holstein-Friesians[J]. Journal of Dairy Science, 2008, 91(1): 385-394. DOI:10.3168/jds.2007-0181 |
| [32] |
LOPEZ-VILLALOBOS N, SPELMAN R J, MELIS J, et al. Genetic correlations of milk fatty acid contents predicted from milk mid-infrared spectra in New Zealand dairy cattle[J]. Journal of Dairy Science, 2020, 103(8): 7238-7248. DOI:10.3168/jds.2019-17971 |
| [33] |
STOOP W M, BOVENHUIS H, HECK J M L, et al. Effect of lactation stage and energy status on milk fat composition of Holstein-Friesian cows[J]. Journal of Dairy Science, 2009, 92(4): 1469-1478. DOI:10.3168/jds.2008-1468 |
| [34] |
ROCHE J R, FRIGGENS N C, KAY J K, et al. Invited review: body condition score andits association with dairy cow productivity, health, and welfare[J]. Journal of Dairy Science, 2009, 92(12): 5769-5801. DOI:10.3168/jds.2009-2431 |
| [35] |
LAKE S L, WESTON T R, SCHOLLJEGERDES E J, et al. Effects of postpartum dietary fat and body condition score at parturition on plasma, adipose tissue, and milk fatty acid composition of lactating beef cows[J]. Journal of Animal Science, 2007, 85(3): 717-730. DOI:10.2527/jas.2006-353 |
| [36] |
VRANKOVIĆ L, ALADROVI Ć J, OCTENJAK D, et al. Milk fatty acid composition as an indicator of energy status in Holstein dairy cows[J]. Archives Animal Breeding, 2017, 60(3): 205-212. DOI:10.5194/aab-60-205-2017 |
| [37] |
GROSS J, VAN DORLAND H A, BRUCKMAIER R M, et al. Milk fattyacid profile related toenergy balance in dairy cows[J]. Journal of Dairy Research, 2011, 78(4): 479-488. DOI:10.1017/S0022029911000550 |
| [38] |
KGWATALALA P M, IBEAGHA-AWEMU E M, MUSTAFA A F, et al. Stearoyl-CoA desaturase 1 genotype and stage of lactation influences milk fatty acid composition of Canadian Holstein cows[J]. Animal Genetics, 2009, 40(5): 609-615. DOI:10.1111/j.1365-2052.2009.01887.x |
| [39] |
PALMQUIST D L, DENISE B A, BARBANO D M. Feed and animal factorsinfluencing milk fat composition[J]. Journal of Dairy Science, 1993, 76(6): 1753-1771. DOI:10.3168/jds.S0022-0302(93)77508-6 |
| [40] |
SAMKOVA E, SPICKA, PESEK M, et al. Animal factors affecting fatty acid composition of cow milk fat: a review[J]. South African Journal of Animal Science, 2012, 42(2): 83-100. |
| [41] |
KAY J K, WEBER W J, MOORE C E, et al. Effects of week of lactation and genetic selection for milk yield on milk fatty acid composition in Holstein cows[J]. Journal of Dairy Science, 2005, 88(11): 3886-3893. DOI:10.3168/jds.S0022-0302(05)73074-5 |
| [42] |
TYBURCZY C, LOCK A L, DWYER D A, et al. Uptake and utilization of trans octadecenoicacids in lactating dairy cows[J]. Journal of Dairy Science, 2008, 91(10): 3850-3861. DOI:10.3168/jds.2007-0893 |
| [43] |
KALA R, SAMKOVA E, KOUBOVA J, et al. Nutritionally desirable fatty acids including CLA of cow's milk fat explained by animal and feed factors[J]. Acta Universitatis Agriculturae et Silviculturae Mendelianae Brunensis, 2018, 66(1): 69-76. DOI:10.11118/actaun201866010069 |
| [44] |
ARTEGOITIA V, MEIKLE A, OLAZABAL L, et al. Milk casein and fatty acid fractions in early lactation are affected by nutritional regulation of body condition score at the beginning of the transition period in primiparous and multiparous cows under grazing conditions[J]. Journal of Animal Physiology and Animal Nutrition, 2013, 97(5): 919-932. |
| [45] |
STADNIK L, DUCHACEK J, TOUSOVA R, et al. Relations between basic milk components and free fatty acid content in Holstein cow milk as lipolysis parameter[J]. Mljekarstvo, 2015, 5(1): 18-25. |
| [46] |
CRANINX M, STEEN A, VAN LAAR H, et al. Effect of lactation stage on the odd- and branched-chain milk fatty acids of dairy cattle under grazing and indoor conditions[J]. Journal of Dairy Science, 2008, 91(7): 2662-2677. DOI:10.3168/jds.2007-0656 |
| [47] |
BRADFORD B J, ALLEN M S. Milk fat responses to a change in diet fermentability vary by production level in dairy cattle[J]. Journal of Dairy Science, 2004, 87(11): 3800-3807. DOI:10.3168/jds.S0022-0302(04)73519-5 |
| [48] |
MILLER N, DELBECCHI L, PETITCLERC D, et al. Effect of stage of lactation and parity on mammary gland cell renewal[J]. Journal of Dairy Science, 2006, 89(12): 4669-4677. DOI:10.3168/jds.S0022-0302(06)72517-6 |
| [49] |
KLIEM K E, SHINGFIELD K J, LIVINGSTONE K M, et al. Seasonal variation in the fatty acid composition of milk available at retail in the United Kingdom and implications for dietary intake[J]. Food Chemistry, 2013, 141(1): 274-281. DOI:10.1016/j.foodchem.2013.02.116 |
| [50] |
HANUS O, KRIZOVA L, SAMKOVA E, et al. The effect of cattle breed, season and type of diet on the fatty acid profile of raw milk[J]. Archives Animal Breeding, 2016, 59(3): 373-380. DOI:10.5194/aab-59-373-2016 |
| [51] |
SOYEURT H, DARDENNE P, DEHARENG F, et al. Genetic parameters of saturated and monounsaturated fatty acid content and the ratio of saturated to unsaturated fatty acids in bovine milk[J]. Journal of Dairy Science, 2008, 91(9): 3611-3626. DOI:10.3168/jds.2007-0971 |
| [52] |
REGO O A, ROSA H J D, REGALO S M, et al. Seasonal changes of CLA isomers and other fatty acids of milk fat from grazing dairy herds in the Azores[J]. Journal of the Science of Food and Agriculture, 2008, 88(10): 1855-1859. DOI:10.1002/jsfa.3289 |
| [53] |
LOPEZ C, BRIARD-BION V, MÉNARD O. Polar lipids, sphingomyelin and long-chain unsaturated fatty acids from the milk fat globule membrane are increased in milks produced by cows fed fresh pasture based diet during spring[J]. Food Research International, 2014, 58: 59-68. DOI:10.1016/j.foodres.2014.01.049 |
| [54] |
GHIZZI L G, DELVALLE T A, ZILIO E M C, et al. Partial replacement of corn silage with soybean silage on nutrient digestibility, ruminal fermentation, and milk fatty acid profile of dairy cows[J]. Animal Feed Science and Technology, 2020, 266: 114526. DOI:10.1016/j.anifeedsci.2020.114526 |
| [55] |
THOMSON A L, HUMPHRIES D J, KLIEM K E, et al. Effects of replacing maize silagewith lucerne silage and lucerne silage chop length on rumen function and milk fatty acid composition[J]. Journal of Dairy Science, 2017, 100(9): 7127-7138. DOI:10.3168/jds.2017-12914 |
| [56] |
SCHULZ F, WESTREICHER-KRISTEN E, MOLKENTIN J, et al. Effect of replacing maize silage with red clover silage in the diet on milk fatty acid composition in cows[J]. Journal of Dairy Science, 2018, 101(8): 7156-7167. DOI:10.3168/jds.2017-14335 |
| [57] |
HALMEMIES-BEAUCHET F A, VANHATALO A, TOIVONEN V, et al. Effect of replacing grass silage with red clover silage on nutrient digestion, nitrogen metabolism, and milk fat composition in lactating cows fed diets containing a 60:40 forage-to-concentrate ratio[J]. Journal of Dairy Science, 2014, 97(6): 3761-3776. DOI:10.3168/jds.2013-7358 |
| [58] |
MANGWE M C, BRYANT R H, BECK M R, et al. Grazed chicory, plantain or ryegrasswhite clover alters milk yield and fatty acid composition of late-lactating dairy cows[J]. Animal Production Science, 2020, 60(1): 107-113. DOI:10.1071/AN18537 |
| [59] |
PETERSEN M B, SOEGAARD K, JENSEN S K. Herb feeding increases n-3 and n-6 fatty acids in cow milk[J]. Livestock Science, 2011, 141(1): 90-94. DOI:10.1016/j.livsci.2011.05.004 |
| [60] |
INEICHEN S, MARQUARDT S, WETTSTEIN H R, et al. Milk fatty acid profile and nitrogen utilization of dairy cows fed ryegrass-red clover silage containing plantain (Plantago lanceolata L.)[J]. Livestock Science, 2019, 221: 123-132. DOI:10.1016/j.livsci.2019.01.018 |
| [61] |
BERNARD L, BONNET M, DELAVAUD C, et al. Milk fat globule in ruminant: major and minor compounds, nutritional regulation and differences among species[J]. European Journal of Lipid Science and Technology, 2018. DOI:10.1002/ejlt.201700039 |
| [62] |
GLASSER F, FERLAY A, CHILLIARD Y. Oilseed lipid supplements and fatty acid composition of cow milk: a Meta-analysis[J]. Journal of Dairy Science, 2008, 91(12): 4687-4703. DOI:10.3168/jds.2008-0987 |
| [63] |
SHINGFIELD K J, BONNET M, SCOLLAN N D. Recent developments in altering the fatty acid composition of ruminant-derived foods[J]. Animal, 2013, 7: 132-162. DOI:10.1017/S1751731112001681 |
| [64] |
SIURANA A, CALSAMIGLIA S. A Meta analysis of feeding strategies to increase the content of conjugated linoleic acid (CLA) in dairy cattle milk and the impact on daily human consumption[J]. Animal Feed Science and Technology, 2016, 217: 13-26. DOI:10.1016/j.anifeedsci.2016.04.013 |
| [65] |
STERGIADIS S, LEIFERT C, SEAL C J, et al. Improving the fatty acid profile of winter milk from housed cows with contrasting feeding regimes by oilseed supplementation[J]. Food Chemistry, 2014, 164: 293-300. DOI:10.1016/j.foodchem.2014.05.021 |
| [66] |
ISENBERG B J, SODER K J, PEREIRA A B D, et al. Production, milk fatty acid profile, and nutrient utilization in grazing dairy cows supplemented with ground flaxseed[J]. Journal of Dairy Science, 2019, 102(2): 1294-1311. DOI:10.3168/jds.2018-15376 |
| [67] |
REGO O A, ALVES S P, ANTUNES L M, et al. Rumen biohydrogenation-derived fattyacids in milk fat from grazing dairy cows supplemented with rapeseed, sunflower, or linseed oils[J]. Journal of Dairy Science, 2009, 92(9): 4530-4540. DOI:10.3168/jds.2009-2060 |
| [68] |
FERLAY A, CHILLIARD Y. Effect of linseed, sunflower, or fish oil added to hay-, or corn silage-based diets on milk fat yield and trans-C18:1 and conjugated linoleic fatty acid content in bovine milk fat[J]. Livestock Science, 2020, 235: 104005. DOI:10.1016/j.livsci.2020.104005 |
| [69] |
LEDUC M, LETOURNEAU-MONTMINY M P, GERVAIS R, et al. Effect of dietary flax seed and oil on milk yield, gross composition, and fatty acid profile in dairy cows: a Meta-analysis and Meta-regression[J]. Journal of Dairy Science, 2017, 100(11): 8906-8927. DOI:10.3168/jds.2017-12637 |
| [70] |
MARQUES J A, DELVALLE T A, GHIZZI L G, et al. Increasing dietary levels of docosahexaenoic acid-rich microalgae: ruminal fermentation, animal performance, and milk fatty acid profile of mid-lactating dairy cows[J]. Journal of Dairy Science, 2019, 102(6): 5054-5065. DOI:10.3168/jds.2018-16017 |
| [71] |
VILLENEUVE M P, LEBEUF Y, GERVAIS R, et al. Milk volatile organic compounds and fatty acid profile in cows fed timothy as hay, pasture, or silage[J]. Journal of Dairy Science, 2013, 96(11): 7181-7194. DOI:10.3168/jds.2013-6785 |
| [72] |
LEIBER F, KREUZER M, NIGG D, et al. A study on the causes for the elevated n-3 fatty acids in cows' milk of alpine origin[J]. Lipids, 2005, 40(2): 191-202. DOI:10.1007/s11745-005-1375-3 |