牛乳中高产共轭亚油酸乳酸杆菌的研究

以云南7个地区的牛乳、水牛乳样品中分离的40株乳酸杆菌为基础,以亚油酸为发酵底物,利用紫外分光光度法对共轭亚油酸(conjugated linoleic acid,CLA)产生菌进行筛选;利用气相色谱法检测高产菌株中CLA的主要异构体及各组分所占比例。本研究得到5株CLA产生菌:M2、M9、M16、M25、M28,产量分别为:25.54、34.56、15.48、20.46、14.79μg/mL,其中菌株M9为CLA高产菌株;气相结果显示菌株M9中CLA的主要异构体为:C18∶2 9c,11t;与对照组相比,油酸、亚油酸和C18∶2 9c,11t的含量变化表明菌株产生C18∶2 9c,11t与油酸和亚油酸有关。本研究为产CLA乳酸菌的筛选和CLA的产生原因提供了科学依据。     

泌乳天数对乳中c9,t11CLA含量的影响

以北方荷斯坦奶牛为研究对象,研究泌乳天数对乳中c9,t11CLA含量的影响。选择饲喂同种饲料的235头健康荷斯坦奶牛,采集同一天的乳样,避免日粮和季节的影响。通过线性分析,探讨泌乳天数对乳中c9,t11CLA含量的影响。结果表明,不同泌乳时期对乳中c9,t11CLA含量没有显著影响（P〉0．05）,通过对泌乳天数与乳中c9,t11-CLA含量的线性模拟发现,R^2值为0.0291。结论：奶牛泌乳天数对乳中c9,t11CLA含量影响很小,所以想提高乳中共轭亚油酸含量,不需要考虑奶牛泌乳天数的不同。     

白地酶脂肪酶选择性酯化分离CLA异构体的研究

本文研究共轭亚油酸异构体的分离方法。利用白地霉脂肪酶(Geotrichumcandidumlipase,GCL)催化合成正丁酯的方法,考察温度、体系水分、酶用量、反应时间、底物配比对脂肪酶催化酯化率和脂肪酸丁酯中c9t11含量的影响。结果表明,经过酯化的脂肪酸丁酯层中c9t11CLA含量达到79.85%,t10c12CLA含量为4.59%;含有13.75%的油酸;c9t11CLA占共轭亚油酸两种异构体总含量的94.56%。形成c9t11CLA正丁醇酯的选择性系数平均为17.80。脂肪酸与正丁醇比例对脂肪酸酯中c9t11CLA含量具有显著性影响,在选取的范围内水分含量、酶用量的影响不显著。要得到较高c9t11CLA含量的脂肪酸产物,反应因子应选择:水分为0.50%,脂肪酸与正丁醇用量比为2.00∶1.00,酶用量为100U/g。白地霉脂肪酶对催化c9t11共轭亚油酸与正丁醇的酯化反应具有较高的选择性,因此,脂肪酶选择性酯化分离CLA异构体的方法是可行的。     

产奶量对乳中c9,t11 CLA含量和乳腺△9-去饱和酶指数的影响

以北方荷斯坦奶牛为研究对象,研究产奶量对乳中c9,t11CLA含量的影响。选择饲喂同种饲料的235头健康荷斯坦奶牛,采集同一天的乳样,避免日粮和季节的影响。通过线性分析,探讨产奶量对乳中c9,t11CLA含量和乳腺△^9-去饱和酶指数的影响。结果表明,奶牛产奶量与乳中c9,t11CLA含量和乳腺△^9-去饱和酶指数的线性模拟发现,其R2值均小于0.01。结论：奶牛产奶量对乳中c9,t11CLA含量和△^9-去饱和酶指数影响很小,所以想提高乳中共轭亚油酸含量,不需要考虑产奶量的不同。     

产共轭亚油酸植物乳杆菌的筛选、鉴定与诱变

从传统泡菜中筛选得到1 株乳酸菌lp15 能够合成共轭亚油酸(CLA),经16S rRNA 全序列分析法和API 系统鉴定法鉴定为植物乳杆菌(Lactobacillus plantarum)。利用人工诱变方法,以lp15 为出发菌株,采用紫外线、硫酸二乙酯(DES)依次诱变处理,经进一步液体发酵复筛获得多株突变菌株,CLA合成能力较出发菌株提高了29.3%～52.2%。其中lp15-2-1 突变菌株为CLA 生成能力最高菌株,MRS 培养液中添加0.2mg/mL LA 培养48h,CLA 产量达30.13μg/mL。经气相色谱(GC)检测分析,产物中cis9, trans11- 共轭亚油酸(c9, t11-CLA)占76.5%,trans10, cis12-共轭亚油酸(t10,c12-CLA)占23.5%。     

优化乳杆菌高产共轭亚油酸的研究进展

共轭亚油酸(CLA)是亚油酸(LA)的一组位置和空间异构体的总称,其中具有生理活性的异构体是c9,t11-CLA和t10,c12-CLA,它们具有丰富的营养价值和医药价值。在乳球菌属和链球菌属等乳酸菌、丙酸杆菌、瘤胃细菌以及其它菌属中,分离纯化得到的亚油酸异构酶,可催化LA异构化为CLA,利用酶法合成CLA可以有效弥补传统化学合成法的缺陷。本文概述了近年来国内外利用紫外、微波、等离子体诱变、离子注入等物理或化学方法诱变、改造亚油酸异构酶,优化产酶条件和酶学特性,还阐述利用定点突变、基因敲除等基因工程方法,对生产菌株进行改造和培养条件优化,提高CLA产量的相关研究,为进一步筛选出高产共轭亚油酸菌株和CLA的产业化应用提供理论依据。     

西北牧区牧民自制酸奶中c9,t11-CLA含量的研究

共轭亚油酸（CLA）是亚油酸的一组几何和位置异构体,具有多种生理功能。反刍动物肉、乳制品是c9,t11-CLA丰富的天然来源。本研究用气相色谱法测定青海、甘南、天祝和肃北4个不同牧区牧民自制酸奶中c9,t11-CLA的含量,并与市售酸奶和牦牛乳中的含量进行对比。结果表明：采用该方法使牧区酸奶中c9,t11-CLA得到很好的分离,测得青海、甘南、天祝和肃北牧区酸奶中c9,t11-CLA的含量分别为1．007、0．782、0,987、1．196rag／ml酸奶;牧区自制酸奶中c9,t110CLA的含量与市售酸奶中的含量差异不显著（p〉0．05）：但含量极显著低于牦牛乳（p〈0．01）。     

共轭亚油酸两种主要异构体冷冻结晶分离工艺研究

应用冷冻结晶技术,对共轭亚油酸两种主要异构体c9,t11 CLA和t10,c12 CLA进行分离。结果表明,通过尿素包合法,去除原料中的饱和脂肪酸,然后在乙醇作溶剂情况下,将乙醇与共轭亚油酸乙酯按18:1配比,置于-56℃低温冷柜中,反应96 h后得沉淀结晶产品,其所含的t10,c12 CLA比c9,t11 CLA高达12.28:1,共轭亚油酸总含量为95.17%。     

自制酸奶乳脂中c9,t11-共轭亚油酸对小鼠免疫调节作用的影响

应用乳酸菌发酵法,添加适当底物和营养物质,实验室自制含共轭亚油酸(CLA)的酸奶,经过提取乳脂、气相色谱检测并对CLA 定量后,确定给予小鼠受试物剂量组,进行共轭亚油酸酸奶的免疫调节功能实验。结果表明：灌胃给予小鼠含0.05g/(kg bw·d) c9,t11-CLA 的乳脂,30d 后可增强小鼠的免疫调节功能,说明酸奶中的c9,t11-CLA 能够显著增加小鼠免疫调节能力。     

c9t11- 和t10c12- 共轭亚油酸抗癌和影响脂质代谢的异同

共轭亚油酸(CLA)是一组位置和构象异构体的总称,异构体c9t11-CLA 和t10c12-CLA 或二者的协同作用赋予了CLA 的许多生理功能,比如抗癌、降低体脂含量、预防糖尿病的发生、降低血脂抑制动脉粥样硬化等;异构体c9t11-CLA 和t10c12-CLA 在结构及来源上存在一定差别--由于双键位置的不同,t10c12-CLA 异构体比c9t11-CLA 异构体更容易氧化;而在生理功能上二者也有差异-- c9t11-CLA 异构体的主要作用是抗癌,而 t10c12-CLA 则是降低体脂、血脂等,大量单一异构体的体外实验研究表明二者在抗癌及脂肪代谢的调节上作用机制也不尽相同。     

Short communication: Postruminal infusion of conjugated linoleic acids negatively impacts milk synthesis in Holstein cows

In view of the potential of rumen-protected conjugated linoleic acid (CLA) as a means to increase the CLA content of bovine milk, a study was undertaken to evaluate the effect of synthetic CLA on milk production and composition. Four Holstein cows received abomasal infusion of: 1) control, no lipid infusion, 2) 150 g/d of synthetic CLA, 31.7% cis-9, trans-11; 30.4% trans-10, cis-12, 3) 150 g/d of safflower oil, and 4) 150 g/d of tallow. Infusion was carried out for 20 to 22 h/d for 11-d periods in a 4 x 4 Latin square design. The milk fat concentration of cis-9, trans-11 and trans-10, cis-12 isomers of CLA was significantly increased with infusion of CLA. However, CLA infusion had other unexpected effects on milk production and composition. Milk yield dropped significantly during the period of CLA infusion. Furthermore, as well as the typical depression in milk fat reported with trans-10 isomers of CLA, other negative effects specific to CLA infusion were observed including a drop in lactose concentration and yield, a drop in protein yield, and an elevated somatic cell count. The important difference between synthetically produced CLA and CLA produced naturally in the cow is the much higher proportion of trans-10 isomers of CLA in the former. The results of this study suggest that the extent of enrichment possible for trans-10 isomers of CLA, and hence the usefulness of synthetic CLA for this purpose, may be limited because of unacceptable effects on milk yield and composition.     

Response of milk fatty acid composition to dietary supplementation of soy oil, conjugated linoleic acid, or both

Thirty-six Holstein cows were blocked by parity and allotted by stage of lactation to 6 treatments to evaluate the effects of dietary soy oil, conjugated linoleic acid (CLA; free acid or calcium salt), or both, on CLA content of milk. Diets were fed for 4 wk and are as follows: (1) control, (2) control + 5% soy oil, (3) control + 1% CLA, (4) control + 1% Ca(CLA)₂, (5) control + 1% CLA + 4% soy oil, and (6) control + 1% Ca(CLA)₂ + 4% soy oil. Rumen volatile fatty acid -concentrations, blood fatty acid concentrations, milk yield, and milk composition were measured weekly or biweekly. Dry matter intake and milk yield were recorded daily. Dietary supplementation of soy oil or CLA had no effect on daily milk yield, milk protein concentration and production, or milk lactose concentration and production. Supplementation of unsaturated fatty acids as soy oil, CLA, or Ca(CLA)₂ increased total fatty acid concentration in plasma, decreased milk fat concentration and production, and had no effect on rumen volatile fatty acid concentrations. The weight percentage of CLA in milk was increased from 0.4 to 0.7% with supplementation of 1% CLA, to 1.2% with supplementation of soy oil, and to 1.3% with supplementation of 1% CLA plus soy oil. Supplementation with Ca(CLA)₂ or Ca(CLA)₂ + soy oil increased the CLA content of milk fat to 0.9 and 1.4%, respectively. In summary, adding 5% soy oil was as effective as supplementing CLA, Ca(CLA)₂, or a combination of 1% CLA (free acid or calcium salt) + 4% soy oil at increasing CLA concentrations in milk fat. Feeding CLA as the calcium salt resulted in greater concentrations of CLA in milk fat than did feeding CLA as the free acid. Dietary supplementation of 5% soy oil or 4% soy oil + 1% CLA as the free acid or the calcium salt increased the yield of CLA in milk.     

Use of conjugated linoleic acid (CLA) enrichments to examine the effects of trans-8, cis-10 CLA, and cis-11, trans-13 CLA on milk-fat synthesis

Conjugated linoleic acid (CLA) supplements have typically been comprised of 4 isomers (trans-8, cis-10; cis-9, trans-11; trans-10, cis-12; and cis-11, trans-13 CLA). Abomasal infusion of pure isomers has shown that trans-10, cis-12 CLA is a potent inhibitor of milk-fat synthesis, whereas cis-9, trans-11 CLA has no effect. However, there appear to be additional fatty acids that inhibit milk-fat synthesis, and the objective of this study was to investigate the effects of additional CLA isomers present in CLA supplements. Four rumen fistulated Holstein cows (141+/-8 DIM, mean+/-SE) were randomly assigned in a 4 x 4 Latin square experiment. Treatments were abomasal infusion of (1) skim milk (negative control), (2) trans-10, cis-12 CLA supplement (positive control), (3) trans-8, cis-10 CLA supplement, and (4) cis-11, trans-13 CLA supplement. Treatments 2 through 4 were targeted to provide 4 g/d of the CLA isomer of interest. The trans-8, cis-10 CLA supplement had no effect on milk-fat yield, whereas the trans-10, cis-12 CLA supplement reduced milk-fat yield by 35%. The cis-11, trans-13 CLA supplement contained some trans-10, cis-12 CLA, and when data were compared to the positive control treatment group, it was obvious that cis-11, trans-13 CLA also had no effect on milk-fat synthesis. Milk-fat content of specific CLA isomers was significantly elevated within respective treatment groups. Milk yield, DMI, and milk protein yield were unaffected by treatment. Overall, trans-10, cis-12 CLA reduced milk-fat synthesis, whereas the other major isomers present in CLA supplements (trans-8, cis-10 CLA and cis-11, trans-13 CLA) had no effect.     

Response to conjugated linoleic acid in dairy cows differing in energy and protein status

The trans-10, cis-12 conjugated linoleic acid (CLA) isomer inhibits milk fat synthesis, whereas milk yield and synthesis of other milk components generally remain unchanged in established lactation. However, in some CLA studies increases in milk yield, milk protein yield, or both have been observed in cows limited in energy, either in early lactation or when grazing pasture. Our objective was to evaluate the performance and monitor peripheral tissue responses to homeostatic signals regulating lipolysis and glucose uptake with CLA supplementation when cows were limited in metabolizable energy in combination with moderate or excess metabolizable protein supply. Holstein cows (n = 48; 112 ± 5 d in milk; mean ± SE) were provided ad libitum access to a diet that met energy and protein requirements for a 16-d standardization interval. Based on performance during this interval, the Cornell Net Carbohydrate and Protein System was used to design energy-limiting rations that provided 80% of metabolizable energy requirements, and these were fed throughout the treatment periods. Cows were randomly allocated to 4 treatments, in a 2-period crossover design. Treatments were 1) moderate metabolizable protein (MP) supply, 2) moderate MP supply + CLA, 3) excess MP supply, and 4) excess MP supply + CLA. Moderate and excess MP supply were at 88 and 117%, respectively, of the MP requirement established during the standardization period, as estimated by the Cornell Net Carbohydrate and Protein System. Each experimental period comprised 16 d, with crossover of CLA within each protein level. The lipid-encapsulated CLA supplement provided 12 g/d of trans-10, cis-12 CLA. Conjugated linoleic acid treatment reduced milk fat yield by 21% but increased milk yield and milk protein yield by 2.6 and 2.8%, respectively. Milk yield and content and yield of both milk protein and fat were unaltered by either protein treatment alone or in combination with CLA. Basal concentrations of glucose, insulin, and nonesterified fatty acids were unaffected by CLA supplementation. The fractional rate of glucose clearance in response to an insulin challenge and the nonesterified fatty acid response to an epinephrine challenge were also not altered by either CLA treatment or MP supply. Overall, the results demonstrate that CLA supplementation when cows are energy-limited allows for repartitioning of nutrients, resulting in increased yields of milk and milk protein, and this can occur without changes in whole-body glucose homeostasis and adipose tissue response to lipolytic stimuli.     

Comparison of calcium salts and formaldehyde-protected conjugated linoleic Acid in inducing milk fat depression

Abomasal infusion studies have shown that trans-10, cis-12 conjugated linoleic acid (CLA) decreases milk fat synthesis. However, supplements of CLA must avoid rumen biohydrogenation for this technology to be applied to ruminants. Rumen protection methods would reduce CLA metabolism in the rumen and increase its supply to the small intestine. Our objective was to compare the efficacy of 2 forms of rumen-protected CLA at inducing milk fat depression. Three mid to late lactation Holstein cows each fitted with a rumen fistula were used in a 3 x 3 Latin square design. Treatments were: 1) control, 2) calcium salts of CLA (Ca-CLA), and 3) formaldehyde-protected CLA (FP-CLA). Supplements were designed to provide 10 g/d of trans-10, cis-12 CLA and were administered intraruminally once per day to ensure exact delivery of amount. Both CLA treatments substantially reduced milk fat yield and content compared with control, with the reductions in milk fat yield averaging 34% for the Ca-CLA treatment and 44% for the FP-CLA treatment. In contrast, milk yield, milk protein yield, and dry matter intake were unaltered by CLA treatment. Efficiency of transfer of trans-10, cis-12 CLA from the supplement into milk fat was 3.2 and 7.0% for Ca-CLA and FP-CLA, respectively. These values are much lower than transfer efficiencies reported for abomasally infused CLA, suggesting that much of the trans-10, cis-12 CLA present in the 2 formulations was biohydrogenated in the rumen. Overall, the extent of the reduction in milk fat yield indicates that both protection formulations are acceptable methods for the formulation of CLA supplements to induce milk fat depression in lactating dairy cows.     

Effects of amide-protected and lipid-encapsulated conjugated linoleic acid supplements on milk fat synthesis

The trans-10, cis-12 isomer of conjugated linoleic acid (CLA) is a potent inhibitor of milk fat synthesis; its ability to reduce milk fat output in a controlled manner as a feed supplement, has potential management applications in the dairy industry. The effectiveness of dietary supplements of trans-10, cis-12 CLA is related to the extent to which their metabolism by rumen bacteria is minimized. A number of processes have been used to manufacture "rumen-protected" feed supplements, and their efficacy can be described by the extent of protection from rumen bacteria as well as postruminal bioavailability. The objective of this study was to investigate the effects of 2 rumen-protected CLA supplements on milk fat synthesis. Using the same initial batch of CLA, supplements were manufactured by the formation of fatty acyl amide bonds or by lipid encapsulation. Three rumen fistulated Holstein cows were randomly assigned in a 3 x 3 Latin square experiment. Treatments were 1) no supplement (control), 2) amide-protected CLA supplement, and 3) lipid-encapsulated CLA supplement. Supplements were fed to provide 10 g/d of the trans-10, cis-12 CLA isomer. Over the 7-d treatment period, 21 and 22% reductions in milk fat yield were observed for the amide-protected and lipid-encapsulated supplements, respectively. Transfer of trans-10, cis-12 CLA into milk fat was also similar for the amide-protected (7.1%) and lipid-encapsulated (7.9%) supplements. Overall, the amide-protected and lipid-encapsulated CLA supplements were equally effective at reducing milk fat synthesis and had no effect on milk yield or dry matter intake.     

An unprotected conjugated linoleic acid supplement decreases milk production and secretion of milk components in grazing dairy ewes

Feeding conjugated linoleic acid (CLA) in a rumen-inert form to dairy ewes has been shown to increase milk production, alter milk composition, and increase the milk fat CLA content. However, few studies have tested ruminally unprotected CLA sources. The objective of this study was to evaluate the effects of an unprotected CLA supplement (29.8% of cis-9,trans-11 and 29.9% of trans-10,cis-12 isomers as methyl esters) on milk yield and composition of dairy ewes. Twenty-four lactating Lacaune ewes were used in a crossover design and received 2 dietary treatments: (1) control: basal diet containing no supplemental lipid and (2) basal diet plus CLA (30 g/d). The CLA supplement was mixed into the concentrate and fed in 2 equal meals after morning and afternoon milkings. Each experimental period consisted of 21 d: 7 d for adaptation and 14 d for data collection. The CLA supplement decreased milk fat content and yield by 31.3 and 38.0%, respectively. Milk yield and secretion of milk lactose and protein were decreased by 8.0, 9.8, and 5.6%, respectively. On the other hand, milk protein content and linear SCC score were 1.8 and 17.7% higher in ewes fed the CLA supplement. The concentration of milk fatty acids originating from de novo synthesis (C16) was increased by 22.6% in ewes fed the CLA supplement. The CLA supplement decreased C14:1/C14:0, C16:1/C16:0, and C18:1/C18:0 desaturase indexes by 25, 18.7, and 0.1%, respectively, but increased the cis-9,trans-11 CLA/trans-11 C18:1 ratio by 8.6%. The concentrations of trans-10,cis-12 CLA and cis-9,trans-11 CLA in milk fat was 309 and 33.4% higher in ewes fed CLA. Pronounced milk fat depression coupled with the deleterious effects on milk yield, milk SCC, and secretion of all milk solids observed in ewes fed an unprotected CLA supplement is likely to be associated with high doses of trans-10,cis-12 CLA reaching the mammary gland, corroborating previous results obtained with dairy cows.     

Effects of a supplement containing trans-10, cis-12 conjugated linoleic acid on bioenergetic and milk production parameters in grazing dairy cows offered ad libitum or restricted pasture

Conjugated linoleic acid (CLA) reduces milk fat synthesis in grazing dairy cows and may improve calculated net energy balance (EBAL). Study objectives were to determine whether CLA-induced milk fat depression could be utilized during times of feed restriction to improve bioenergetic and milk production parameters. Twelve multiparous rumen-fistulated Holstein cows (204 ± 7 d in milk) were offered ad libitum (AL) or restricted (R) pasture and abomasally infused twice daily with 0 (control) or 50 g/d of CLA (CLA; mixed isomers) in a 2-period crossover design. Treatment periods lasted 10 d and were separated by a 10-d washout period. Milk and plasma samples were averaged from d 9 and 10, and EBAL was calculated from d 6 to 10 of the infusion period. Pasture restriction reduced the yield of milk (3.9 kg/d) and milk components. The CLA treatment reduced milk fat yield by 44 and 46% in AL and R, respectively. There was no effect of CLA on milk yield or milk lactose content or yield in either feeding regimen; however, CLA increased the milk protein content and yield by 7 and 6% and by 5 and 8%, in AL and R, respectively. The CLA-induced changes to milk fat and protein doubled the protein:fat ratio in both AL and R. Calculated EBAL improved following the CLA infusion (−0.44 vs. 2.68 and 0.38 vs. 3.29 Mcal/d for AL and R, respectively); however, CLA did not alter plasma bioenergetic markers. Data indicate that during short periods of nutrient limitation, supplemental CLA may be an alternative management tool to enhance protein synthesis and improve the milk protein:fat ratio and calculated EBAL in cows grazing pasture. Further studies are required to determine whether CLA is effective at improving bioenergetic and production parameters during more severe or longer term nutrient restriction.     

Reduced fatty acid synthesis and desaturation due to exogenous trans10,cis12-CLA in cows fed oleic or linoleic oil

To determine effects of an elevated supply of cis9,trans11-18:2 (9/11CLA) or trans10,cis12-18:2 (10/12CLA) on de novo synthesis and desaturation of long-chain fatty acids, four Holstein cows fed high-oleic sunflower (OLE) or high-linoleic safflower oil (LIN) at 2.5% of DM were infused (0.625 g/h) with 9/11CLA or 10/12CLA for 48 h via the abomasum. Treatments were assigned in a 2 x 2 factorial design. The assigned diets were fed for 11 d before each 48-h infusion period. Milk samples were obtained at 12 and 0 h before infusion and at 12-h intervals from 0 to 96 h. Concentrations of trans11-18:1 and 18:2n-6 in arterial plasma phospholipid, triglyceride, and FFA fractions were greater due to feeding LIN compared with OLE. Infused 9/11CLA and 10/12CLA were incorporated into plasma triglycerides and FFA primarily. Exogenous 10/12CLA also was found in plasma phospholipids. Milk yield and DMI were not affected by treatments. Percentages and yields of protein, lactose, and SNF in milk also were not affected by treatments. Milk fat percentage and yield, however, decreased 25% from 0 to 96 h in response to infusion of 10/12CLA compared with 9/11CLA. Yields of trans11-18:1, 9/11CLA and 18:2n-6 in milk fat before infusion were higher when LIN was fed compared with OLE. Infusion of 9/11CLA, regardless of diet, increased 9/11CLA in milk fat by 44%. Although 10/12CLA was not detectable in milk fat before infusion, it averaged 6 mg/g of total fatty acids and 2 g/d after 48 h. At 48 h, recovery in milk of infused 9/11CLA was 16% compared with 8% for 10/12CLA. Yields of saturated 6:0 to 16:0, cis9-18:1, 9/11CLA, and 20:4n-6 were reduced by 10/12CLA infusion. Due to a 40% increase in the concentration of 18:0 by 48 h of 10/12CLA infusion, however, yield of 18:0 was not affected. Ratios of cis9-18:1/18:0, 9/11CLA/trans11-18:1, and 20:4n-6/18:2n-6 in milk fat decreased in response to infusion of 10/12CLA, regardless of diet. At peak concentration of 10/12CLA, reductions in cis9-18:1 and saturated 4:0-16:0 yields accounted for 36% and 53% of the decrease in total fatty acid yield. Results indicated 10/12CLA alters lipid metabolism in the bovine mammary gland by simultaneously reducing de novo synthesis and desaturation. Furthermore, milk triglyceride synthesis may have a stringent requirement for endogenously synthesized oleic acid.