反-10,顺-12共轭亚油酸、丙酸盐和醋酸盐对奶牛乳脂产量和乳成分影响的研究

奶牛日粮引起的乳脂降低综合征(MFD)是由于瘤胃脂类代谢发生改变,产生某些特定的异构体(如反-10,顺-12共轭亚油酸),从而抑制乳脂的合成,然而这些异构体在瘤胃的流出量并不完全代表乳脂下降的观测值。高精饲料日粮引起MFD的同时产生大量的丙酸,这表明丙酸和反-10,顺-12共轭亚油酸(CLA)可能共同抑制乳脂的合成。本试验旨在研究丙酸和反-10,顺-12CLA相结合(均为乳脂合成的抑制剂)对奶牛乳脂分泌的影响,以及2种养分(乙酸和丙酸)对乳脂合成的对立作用。选取6头荷斯坦奶牛,采用6×6拉丁方设计,试验持续21d(养分灌注14d)。试验处理分别为:对照组;瘤胃灌注1500g/d乙酸(A);瘤胃灌注800g/d丙酸(P);十二指肠灌注1.6g/d反-10,顺-12CLA(CLA);瘤胃灌注750g/d乙酸+400g/d丙酸(A+P);十二指肠灌注1.6g/d反-10,顺-12CLA(CLA)+瘤胃灌注800g/d丙酸(CLA+P)。研究结果表明,处理A和P组奶牛干物质采食量(DMI)下降;与对照组相比,处理P和CLA组乳脂率和乳脂产量分别下降了9%和15%;处理A组乳脂率提高了6.5%,但并不影响乳脂产量(奶产量下降的原因);A和P、CLA和P对乳脂和乳脂肪酸率、乳脂产量的作用是可加性的(A+P和CLA+P);当灌注等量的反-10,顺-12CLA时,添加丙酸组乳脂下降高达40%,显著高于反-10,顺-12CLA单独灌注组;CLA+P组与高精饲料引起的MDF乳脂肪酸组成相似。因此,本试验条件下,反-10,顺-12CLA、乙酸和丙酸对乳脂合成均有作用,且具有可加性。高精饲料日粮引起的MDF,除了考虑反-10,顺-12CLA的抑制作用,丙酸也能起到抑制乳脂合成的作用。     

奶牛乳脂降低综合症的生物氢化理论研究进展

脂肪是牛奶中受日粮影响最大的成分。奶牛饲喂高精料日粮或高不饱和油脂均在一定程度上导致乳脂降低综合症的发生，进而影响牛奶加工产品。截至目前，乳脂降低症的主要生物学机制是乳脂合成底物不足以及瘤胃氢化时产生的反式脂肪酸或其它特殊脂肪酸产物抑制了乳腺脂肪酸合成途径所致。作者仅就后者生物氢化理论的研究进展进行综述，力图为相关科技工作者提供一定的参考。     

短链脂肪酸调控奶牛乳腺乳脂合成作用机制的研究进展

短链脂肪酸是胃肠道微生物发酵的主要产物,不仅作为乳脂合成前体物直接参与乳腺内脂肪酸的从头合成,还作为信号分子调节乳腺脂肪酸代谢,进而调控乳脂的合成.本文从短链脂肪酸对乳脂合成的影响以及短链脂肪酸调控乳腺乳脂合成的分子机制2方面,综述了短链脂肪酸调控奶牛乳腺乳脂合成的作用机制,为奶牛乳脂合成机制的相关研究提供理论依据.     

反-10,顺-12共轭亚油酸真胃梯度灌注对奶山羊乳脂合成的影响

旨在研究反-10,顺-12CLA对山羊乳脂合成抑制作用的效果及机制.选用4只安装永久性真胃瘘管和做了颈动脉游离的崂山奶山羊,4×4拉丁方设计,4个试验处理为真胃灌注0、2、4和8 g·d-1含有反-10,顺-12CLA的共轭亚油酸产品.结果表明:①真胃灌注CLA对奶山羊产奶量、采食量无明显影响;与对照组相比,CLA灌注水平为4和8 g·d-1时,奶山羊的乳脂率和乳脂产量均显著降低(P<0.01),乳蛋白含量显著升高(P<0.01),但乳蛋白产量变化不明显.CLA处理对乳糖、无脂固形物(SNF)含量和产量无显著影响(P>0.05).②与对照组相比,CLA处理显著降低了游离脂肪酸(NEFA)的乳腺吸收率(P<0.05).乙酸乳腺吸收率随CLA灌注量增加有先上升后下降的趋势(P=0.07).丁酸的乳腺吸收率有上升趋势(P=0.07).③真胃灌注CLA显著提高了乳脂中C16脂肪酸的总含量(P<0.05),对乳腺从头合成脂肪(C4-C14:1)的含量和血液吸收脂肪酸(C16以上)的含量无显著影响.随CLA添加量的升高,乳脂脂肪酸中顺-9,反-11CLA(P<0.01)、反-10,顺-12CLA(P<0.05)、顺-9,顺-11CLA(P<0.05)和反-9,反-11CLA(P<0.01)的含量逐渐升高.④真胃灌注CLA降低了C14:1、C16:1和>C16脂肪酸的产量(P<0.05),对C16:0脂肪酸的产量没有影响,但表观值随CLA灌注量的增加而降低(P=0.19).与对照组比较,8 g·d-1CLA灌注组的C4-C14:1、C16+C16:1和>C16脂肪酸的产量分别下降了42.68%、36.15%和55.59%.⑤与对照组相比,CLA真胃灌注升高了C14:0/C14:1(P<0.01)、C16:0/C16:1和反-11C18:1/顺-9,反-11CLA的比例(P<0.05),表明CLA真胃灌注降低了△9-脱饱和酶的活性.⑥对8 g·d-1CLA灌注组与对照组(活体采样)乳腺组织中乙酰CoA羧化酶mRNA表达量的分析表明,CLA真胃灌注降低了乙酰CoA羧化酶mRNA的表达水平(P<0.01).反-10,顺-12CLA既抑制血液NEFA用于乳脂合成,也抑制乳腺脂肪酸的从头合成.     

国际科技资讯

<正>西班牙研究饲料中的亚麻籽油对羊乳脂中反-10,顺-15十八碳二烯酸含量的影响近年来研究人员在反刍动物消化道内容物及肌肉和脂肪组织中检测出了反-10,顺-15十八碳二烯酸,并对其进行了表征,但乳及乳制品中是否含有这种脂肪酸尚不明确。近日,西班牙科研人员定量测定了乳脂肪中的反-10,顺-15十八碳二烯酸,以期更好地了解其代谢来源,从而有助于解释饲料成分影响     

奶牛营养代谢对乳脂合成调控机制的研究进展

综述瘤胃挥发性脂肪酸变化模式对乳脂前体的影响，胰岛素一葡萄糖在脂肪组织动员过程中激素、营养物质、脂蛋白脂肪酶和激素敏感脂肪酶的动态变化以及不同脂肪酸及其异构体对乳脂合成的影响。并对营养因素影响乳脂合成的综合效应进行了阐述。     

饲料中可影响牛奶乳脂率的成分

牛瘤胃代谢产物中的挥发性脂肪酸即乙酸、丙酸和丁酸的比例结构,对奶牛产奶量和乳脂率有重大影响。乙酸被吸收后,通过血液被输送到乳腺,用以合成乳脂肪中的一系列短链脂肪酸;丙酸被吸收后,输送到肝脏,成为合成葡萄糖的原料;丁酸是乳脂肪中的短链脂肪酸,也可与乙酰辅酶A缩合形成高级脂肪酸。乙酸、丁酸比例增加,有利于提高奶牛乳脂率。     

trans-10,cis-12共轭亚油酸抑制牛乳脂的合成及乳脂合成相关基因的表达

奶牛日粮添加共轭亚油酸 (CL A)抑制乳脂合成 ,已经证明这是 trans- 10 ,cis- 12 CL A异构体的特殊功能。本试验主要探讨 trans- 10 ,cis- 12 - CL A抑制乳脂合成的机制。试验动物为 4头泌乳晚期的经产荷斯坦奶牛 ,采用 2× 2交叉试验设计。每种处理包括 5 d真胃灌注脱脂乳或将 trans-10 ,cis- 12 - CL A乳化于其中的脱脂乳。灌注的第 5 d进行乳腺活体切片检测 ,一部分乳腺组织用于分析乙酰辅酶 A羧化酶、脂肪酸合成酶、Δ9-去饱和酶、脂蛋白脂酶、脂肪酸结合蛋白、磷酸甘油酰基转移酶的 m RNA表达情况。另一部分乳腺组织用于脂肪合成能力的评定。灌注 tuans- 10 ,cis- 12 - CL A使乳脂肪含量及产量分别降低 4 2 %和 4 8% ,同时乳中 trans-10 ,cis- 12 - CL A含量从低于 0 .1m g/ g增加至 4 .9mg/ g。 C4～ C1 6 脂肪酸的减少量占乳脂总减少量的 6 3%。通过对几种特定脂肪酸双键的分析结果表明 ,trans- 10 ,cis- 12 - CL A对脂肪酸组分变化的另外一种影响与 Δ9-去饱和酶的降低一致。通过与放射性标记乙酸一起进行的乳腺移植培养发现 ,给奶牛饲喂 trans- 10 ,cis- 12 - CL A后 ,脂肪合成能力降低 82 % ,乙酸氧化为 CO2 减少 6 1% ;同时 ,灌注 trans- 10 ,cis- 12 - CL A还使上述几种酶的 m RNA表达减少     

共轭亚油酸调控牛奶乳脂合成的机理

共轭亚油酸(CLA)是一族18碳二烯酸结构和位置异构体的总称,对乳脂肪酸组分和乳脂合成有显著影响,尤其trans10,cus12 CLA可引起乳脂降低综合症(MFD).作者主要针对CLA与奶牛脂肪代谢的关系做了简述.     

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。     

饱和脂肪酸对高温环境条件下泌乳中期奶牛产奶性能及牛奶脂肪酸组成的影响

本文旨在研究饱和脂肪酸对高温环境条件下泌乳中期奶牛产奶性能和牛奶中脂肪酸组成的影响.选择产后150～210 d的中国荷斯坦奶牛48头,根据产奶量、分娩时间和胎次分为对照组(SFA 0)、1.5%(SFA 1.5)和3.0%(SFA 3.0)饱和脂肪酸试验组.试验期间牛舍最小湿热指数(THI)在72以上.试验结果,日粮添加饱和脂肪酸提高4%乳脂校正产奶量(P＜0.05),SFA 1.5与SFA 3.0脂肪组之间差异不显著(P＞0.05).乳脂和总固形物含量,SFA 3.0组高于对照组(P＜0.05),SFA 1.5组与对照组和SFA 3.0组间差异均不显著(P＞0.05).乳蛋白、乳糖、乳尿素氮和乳中体细胞评分各组间差异均不显著(P＞0.05).日粮添加饱和脂肪酸的量对乳脂和乳总固形物呈线性增加(P＜0.05),对乳蛋白的含量呈二次曲线增加(P＜0.05).中链、长链、长链不饱和、总不饱和、t10c12CLA、总饱和脂肪酸、长链不饱和与总不饱和脂肪酸的比例各组间差异均不显著(P＞0.05).SFA 3.0组短链脂肪酸低于对照组(P＜0.01)和SFA1.5组(P＜0.05),SFA 1.5组与对照组差异不显著(P＞0.05).日粮添加饱和脂肪酸呈线性降低乳中短链脂肪酸含量(P=0.03)和c9t11CLA含量(P＜0.01),SFA 0、SFA1.5和SFA 3.0组乳中c9t11CLA含量分别为0.72、0.64和0.55 g/100 g脂肪.结果表明,泌乳中期热应激奶牛日粮添加饱和脂肪酸可显著提高产奶量、乳脂率和乳中总固形物含量;对乳中脂肪酸组成无明显影响;c9t11CLA含量显著降低,但仍在正常范围之内.     

不同能量物质对泌乳奶牛产奶性能的影响

本文探讨了不同能量补充物质对泌乳奶牛生产的影响。,以麸皮作对照,用全棉籽、膨化全脂大豆和脂肪酸钙作为能量补充物质,35d试验结果显示,奶牛产奶量分别提高了6．7％、14．4％和18．2％．．乳脂肪分别提高19．（／9％、11．82％和11．21％、经济效益分别比对照组提高4．20、5．36和8．72．＇L／（头·d）!试验表明,全棉籽、膨化全脂大豆和脂肪酸钙作为能量补充物质,可减轻夏季热应激,提高牛奶产量和牛奶品质,尤以脂肪酸钙效果最佳。     

Challenges in enriching milk fat with polyunsaturated fatty acids

Milk fatty acid composition is determined by several factors including diet. The milk fatty acid profile of dairy cows is low in polyunsaturated fatty acids, especially those of the n-3 series. Efforts to change and influence fatty acid profile with longer chain polyunsaturated fatty acids have proven challenging. Several barriers prevent easy transfer of dietary polyunsaturated fatty acids to milk fat including rumen biohydrogenation and fatty acid esterification. The potential for cellular uptake and differences in fatty acid incorporation into milk fat might also have an effect, though this has received less research effort. Given physiological impediments to enriching milk fat with polyunsaturated fatty acids, manipulating the genome of the cow might provide a greater increase than diet alone, but this too may be challenged by the physiology of the cow.     

牛奶中脂肪酸与常规营养成分含量的影响因素分析

本试验旨在研究季节对牛奶中脂肪酸含量的影响以及不同地区、泌乳期、季节和胎次对牛奶常规营养成分的影响。对来自DHI中心的9872份牛奶样本中的脂肪酸含量数据和3430份牛奶样本中的乳脂、蛋白质、乳糖与总固形物含量数据,按季节、地区、泌乳期、胎次进行分组,然后进行单因素方差分析。结果如下:(1)季节对牛奶中脂肪酸含量产生极显著影响(P<0.01):夏季乳脂中饱和脂肪酸极显著高于其他季节(P<0.01),不饱和脂肪酸极显著低于其他季节(P<0.01)。游离脂肪酸春季最高且极显著高于其他季节(P<0.01)。(2)不同地区对乳脂、乳糖、总固形物产生极显著影响(P<0.01):宁夏蛋白质含量最高,且显著高于河南、湖北与内蒙古(P<0.05)。而宁夏与内蒙古之间乳脂、乳蛋白、总固形物无显著差异(P>0.05)。湖北与宁夏牛奶总成分含量较高。(3)泌乳期对牛奶成分含量产生极显著影响(P<0.01):泌乳前期乳脂、蛋白质、总固形物含量最低,且显著低于泌乳中期、泌乳晚期、泌乳延长期(>305d)(P<0.05)。泌乳前期与泌乳中期乳糖含量较高,且极显著高于泌乳晚期、泌乳延长期(P<0.01)。(4)不同季节对乳常规营养成分含量产生极显著影响(P<0.01):夏季各项指标最低,且极显著低于春季、秋季、冬季(P<0.01)。(5)不同胎次对乳蛋白、乳糖、总固形物含量产生极显著影响(P<0.01),一胎牛乳中各种成分含量最高,且极显著高于三胎次奶牛(P<0.01)。     

Diet-induced milk fat depression: Association with changes in milk fatty acid composition and fluidity of milk fat

This experiment was designed to examine changes in milk fatty acids during fish oil-induced milk fat depression (MFD) and to test the theory that these changes are related to milk fat fluidity. The experiment was divided into three periods: 1) Baseline: all cows (n = 12) received a high fiber diet without fish oil (FO) for 12 days; 2) Treatment: 4 cows/group received the following treatments for 21 days: a) Low fiber diet without FO (LF), b) High fiber diet + FO (HF + FO) and c) Low fiber diet + FO (LF + FO); 3) Post-treatment: cows returned to the baseline diet and were monitored for 12 days. FO was included at 1.6% DM and HF and LF diets had 40 and 26% NDF, respectively. Milk fat content and yield were unchanged by the LF diet, but were reduced by FO diets at both dietary fiber levels and recovered in the post-treatment period. FO diets caused a pronounced reduction in stearic and oleic acid concentrations in milk fat and an equally pronounced increase in trans-18:1 fatty acid concentrations. Milk fat mean melting point (MMP) was correlated with MFD (r = 0.73) and with milk oleic acid concentration (r = − 0.92). The ratio of oleic:stearic in milk fat increased gradually and consistently in response to FO. Trans-C18:1 isomers with double bounds at carbon ≤ 10 increased with greater MFD and those with double bonds at carbon ≥ 11 decreased with greater MFD. Trans-9 cis-11 CLA explained more than 80% of MFD and was strongly correlated with trans-10 C18:1. Maintenance of MMP below 39–40 °C suggests that the mammary gland was able to secrete only milk fat with adequate fluidity and that MFD could be an adaptation mechanism to prevent secretion of milk with higher MMP.     

Supplementation with bypass fat in silvopastoral systems diminishes the ratio of milk saturated/unsaturated fatty acids

This study was conducted to evaluate if supplementing bypass fat to cows under silvopastoral systems, increases the concentration of unsaturated fatty acids in milk, thus improving the saturated/unsaturated ratio without a negative effect on total milk yield in fat or protein. Two concentrations of two different sources of bypass fat were evaluated for 40 days, each in a group of 24 multiparous Lucerna (Colombian breed) cows. A cross-over design of 8 Latin squares 3 × 3.was used The variables submitted to analysis were body condition, daily milk production and milk composition. Body condition, milk yield and milk quality were not different but there was a significant decrease in the amount of saturated fatty acid in both experiments while the unsaturated fat increased significantly in experiment 1 and remained stable in experiment 2. Results, such as these have as far as we know, not been reported previously and they provide an approach for the improvement of milk as a “functional food”.     

Changes in fatty acid composition of milk from lactating dairy cows during transition to and from pasture

Five Holstein cows producing an average of 25.4 ± 6.4 kg/d and 347 ± 111 days in milk were used to study the changes in fatty acid composition in milk from lactating dairy cows during transition to and from pasture. The 45-d experiment was divided into 3 periods. During the first 2 d of the experiment (Period I), cows were fed a TMR diet containing 50% conserved forage and 50% grain. On day 3, cows were turned out to pasture and remained on all-pasture diet for 29 d (Period II). On day 32, cows were withdrawn from pasture and offered a TMR diet until day 45 (Period III). Milk yield was recorded daily, and milk fat content and fatty acid (FA) composition were determined daily for composite samples collected from a.m. and p.m. milkings. Data were analyzed using spline regression (H₀ = zero slope) to determine whether there was any change in the concentration of a particular fatty acid after a specific time or whether it had stabilized. Cows produced an average of 25.2 ± 5.5, 13.7 ± 5.6, and 12.1 ± 4.8 kg/d of milk with 3.6, 4.2, and 3.6% fat during pre-pasture, pasture, and post-pasture diets, respectively. The conjugated linoleic acid (CLA) content was 0.45% of total fat during pre-pasture, reached to a maximum of 2.53% on day 23 into pasture and plateaued thereafter for the period. Milk fat C_18:1 t-11 content was 2.89% of total fat during pre-pasture, reached a maximum of 7.95% after day 22 in pasture, and plateaued afterwards. The C_18:2 content declined gradually from pre-pasture to pasture diet with no further decrease observed after day 22, while C_18:3 content increased until day 7 on pasture. The post-pasture CLA content in milk fat reached a value similar to pre-pasture within 4 days after the cows were withdrawn from pasture. No change in other fatty acids was observed after day 7 once the cows were switched to post-pasture diet. In the present study, it took 23 days to establish the highest level of CLA in milk fat after turning cows out to pasture, whereas only 4 days were needed to bring it back to the original level once the cows were withdrawn from pasture. Other milk fatty acids were stabilized around day 23 after turning cows out to pasture and by day 7 after being withdrawn from pasture and put back on a TMR diet inside the barn.     

Fat and cholesterol content and fatty acid composition of mares' colostrums and milk during five lactation months

In this study, the effect of the lactation stage on changes in the fat and cholesterol content and fatty acid composition of colostrum and milk of Wielkopolska mares' was investigated. Colostrum and milk samples from 10 lactating mares were collected at the beginning of lactation, on the 1st and 2nd day after foaling and then, starting from the first month of lactation, at 4 weeks' intervals up to the fifth month of lactation. Statistically significant differences were found between mares' colostrum and milk in the fat and cholesterol content as well as in the percentage rate of total fatty acids which occurred in significant quantities. Together with the lengthening of the lactation time, the content of fat and cholesterol in the mares' milk was observed to decrease. The authors also found a significant impact of the lactation period on changes in the ratio of polyenoic fatty acids from the n-6 to n-3 family. Bearing in mind the fat and cholesterol content and a more favourable (from the nutritional point of view) ratio of fatty acids from the family of n-6 to n-3, it is recommended to collect milk from mares in the 4th and 5th month of lactation.     

Effects of peripartum biotin supplementation of dairy cows on milk production and milk composition with emphasis on fatty acids profile

Forty Holstein dairy cows receiving a 38% concentrate diet based on maize silage were assigned to either a control group, either a biotin group, receiving 20 mg of biotin per day from 15 days before expected calving date and for 120 days after calving. Milk production was measured daily, milk fat content, protein content, urea and somatic cell counts were determined weekly from week 2 to week 17 of lactation. The profile of milk fatty acids was determined at weeks 3 and 10. Plasma glucose and blood beta-hydroxybutyrate were determined before calving and at weeks 1, 2, 3, 5, 7 and 10 of lactation.

Biotin supplementation resulted in an increased milk production in multiparous cows during weeks 2 to 6, but the effect was no more significant between 7 and 17 weeks of lactation. Milk protein percent was decreased by 0.1% in multiparous cows. Milk fat content was not affected by biotin, and milk fat daily production tended to increase during early lactation. In milk fat, biotin supplementation tended to decrease the proportion of fatty acids with less than 16 carbons at week 3, but the daily amount was not affected. Biotin tended to decrease biohydrogenation intermediates, increased C16:1 at week 3, and tended to increase cis-9 C18:1 at weeks 3 and 10. After 7 weeks of lactation, biotin tended to increase blood beta-hydroxybutyrate in multiparous cows with values remaining in a normal range, and decreased plasma glucose in primiparous cows. These modifications of plasma parameters, milk protein content and profile of milk fatty acids could be due to a higher lipid mobilisation from adipose tissue driven by the increased milk production.     

Effects of Turnout to Pasture and Dietary Fat Supplementation on Milk Fat Composition and Conjugated Linoleic Acid in Dairy Cows

Turnout to pasture involves considerable changes in the feed intake and metabolism of dairy cows. The aim of this study was to investigate how these changes affect milk production and milk fat composition, in cows selected for high (HFI) or low (LFI) milk fat content producing the same yield of 4% fat-corrected milk. Furthermore, two different concentrates, with high or low inclusion of soya oil, were studied. The experiment was conducted with 44 multiparous mid-lactating cows over a 4 week period. Samples of milk and blood were obtained before turnout to pasture, during transition to pasture and when cows were adapted to pasture. Milk yield decreased with 3.6 kg energy-corrected milk (ECM) on average during the first 5 days after turnout to pasture. This decrease, together with a drop in plasma insulin and increased plasma non-esterified fatty acids (NEFA), indicated nutritional insufficiency at turnout to pasture. Milk fat composition changed towards more long-chain fatty acids (LCFA) and fewer de novo synthesized fatty acids. This was probably caused by an increased supply of LCFA of feed and body origin to the udder. LFI cows showed higher levels of conjugated linoleic acid at pasture than HFI cows.