热应激对泌乳奶牛泌乳性能和乳品质的影响及其机制

发布时间：2018-05-30 13:18

本文选题：奶牛 + 热应激　；参考：《南京农业大学》2015年硕士论文

【摘要】：本研究旨在研究热应激对泌乳奶牛泌乳活动造成的影响,并对这些影响的机制进行初步研究。研究包括以下三个方面。1、高温气候环境对泌乳奶牛机体代谢和泌乳性能的影响选取6头相同泌乳期的荷斯坦奶牛,正常饲喂和饮水。实验期从6月29日至8月5日,共计35天。每日10:00和18:00记录气温,统计产奶量,每周取全天奶样检测乳蛋白、乳脂肪和乳糖含量。于实验开始第1周和最后1周采集颈静脉血液检测相关生化指标和血液中相关激素的含量。结果表明:随着环境气温由26 ℃升高至38 ℃,实验奶牛均产奶量由15.2kg/d下降至10kg/d;乳蛋白产量由0.47kg/d下降至0.30 kg/d,乳脂肪产量由0.46kg/d下降至0.28kg/d,乳糖产量由0.71kg/d降至0.46kg/d。血液中 TP(94.18±0.35115.07±1.04g/L,p=0.049),球蛋白(69.58±0.2088.95±1.10g/L,p=0.045)和葡萄糖(2.88±0.043.54±0.11 mmol/L,p=0.03)含量均显著升高;LDL-C(0.18±0.030.29±0.01mmol/L,p=0.004)和 AKT(4.17±0.3135.50±4.15 U/L,p=0.004)极显著升高;HDL-C 显著降低(3.23±0.082.20±0.04 mmol/L,p=0.033)。血液中 GH(1.19±0.031.54±0.06ng/mL,p=0.037)和 IGF-I(80.05±10.62-100.72 ± 21.78ng/mL,p=0.048)含量显著升高;皮质醇(288.21 ±49.73573.76 ±11.71ng/mL,p=0.009)含量极显著升高,胰岛素(22.48±2.5325.66±1.95IU/L,p=0.057)和胰高血糖素(597.18±58.11658.02±49.47pg/mL,p=0.06)浓度均有升高。结果提示:在中国南京夏季高温高湿条件下,可诱发奶牛发生热应激,奶牛内分泌和营养代谢均发生变化,表现泌乳量减少,乳品质降低。2、热应激时乳成分前体物重分配变化与乳品质降低的关系研究通过探讨血液中氨基酸和游离脂肪酸等"乳成分前体物"与乳脂肪、乳蛋白合成之间的关系,揭示热应激时泌乳奶牛乳品质降低的可能机制。实验动物饲养与处理同第三章。实验开始和结束时采集颈静脉血液,RP-HPLC和ELISA发分别检测血液中游离氨基酸和游离氨基酸含量。结果表明:随着气温的升高(由26 ＞升高至最高38 ＞),乳脂肪、乳蛋白含量降低,实验奶牛血液中总NEFA显著升高(178.20±16.70272.42±20.53μg/mL,p=0.025);Glu、Asp、Gly 和 Val 等主要的生糖氨基酸(811.28±259.223254.05±666.79μmol/L,p=0.035)以及 Leu、Ile 等生酮氨基酸均升高或显著升高(169.26±32.27502.76±105.50 μmol/L,p=0.046);总支链氨基酸(Val、lle、Leu)含量显著增加(198.36±52.571474.85±355.83μmol/L,p=0.02870.05),在必需氨基酸中的所占比例由54.75%增至67.89%。结论:在夏季高温奶牛热应激状态下,乳脂肪、乳蛋白含量均降低,但血液中NEFA,游离氨基酸,特别是支链氨基酸含量显著升高。提示热应激时血液中高水平的NEFA和游离氨基酸并未完全用于乳脂肪和乳蛋白的合成,还发挥了除此之外的供能、糖异生及免疫反应等其他作用,而后者的作用优先于参与乳脂肪、乳蛋白的合成。热应激时乳成分前体物的重分配变化可能是导致乳蛋白、乳脂肪下降的机制之一。3、热应激致奶牛乳成分前体物发生重分配机制初探在前两章的实验中,我们发现热应激可以引起奶牛乳蛋白和乳脂肪的前体物发生重分配,并引起牛奶中乳蛋白和乳脂肪含量降低。为了探究乳蛋白和乳脂肪前体物重分配引起乳成分含量降低的机制,本部分实验对实验奶牛进行了肝脏样品组织采集。采用Real-time PCR方法,对奶牛肝脏内糖异生关键酶PC和PEPCK基因,肝脏组织中 GHR、IGFR,HSP70 及 Keap1-Nrf2 通路及其下游 HO1,GCLM,NQO1,GCLC 等蛋白进行了 mRNA表达检测。结果发现:在热应激时,奶牛肝脏内PC(0.917±0.0081.08±0.025,p=0.045)和PEPCK(0.87±0.0091.29±0.132,p=0.032)表达水平显著升高;GHR(1.05±0.121.39±0.02,p=0.007)表达水平极显著上调,IGFR(1.07±0.051.28±0.018,p=0.036)显著上调;肝脏中HSP70(0.35±0.1651.55±0.012,?=0.006)表达极显著增高;Keap1(1.07±0.241.32±0.27,p=0.046)和Nrf2(1.59±0.181.73±0.19,p=0.049)基因表达显著升高,其下游4个基因中,HOl(0.98±0.081.19±0.02,p=0.037)和NQO(0.92±0.081.43±0.02,p=0.026)表达显著提高,GCLM(0.69±0.100.97±0.05,p=0.059)和GCLC(0.84±0.071.29±0.11,p=0.061)表达有升高,但差异不显著。结果提示:热应激时肝脏中糖异生作用和抗应激作用均增强,血液中升高的乳蛋白、乳脂肪前体物在GH-IGF-I轴和Keap1-Nrf2-ARE信号通路的介导下更多地参与了糖异生过程和抵抗细胞的应激损伤,过多消耗了乳成分合成的前体物,减少了乳蛋白和乳脂肪的合成。
[Abstract]:The purpose of this study was to study the effects of heat stress on lactation activities of lactating dairy cows and to study the mechanism of these effects. The study included the following three aspects: the following three aspects: the effects of high temperature climate on the metabolism and lactating performance of lactating dairy cows, 6 Holstein cows with the same lactation period, normal feeding and drinking water. From June 29th to August 5th, a total of 35 days. The temperature was recorded at 10:00 and 18:00 per day, milk production was measured, milk protein, milk fat and lactose content were taken every week. The biochemical indexes of the jugular blood test and the content of related hormones were collected at the first first and the last 1 weeks of the experiment. The results showed that the environmental temperature was 26 degrees centigrade. The milk yield of dairy cows decreased from 15.2kg/d to 10kg/d at 38 C, milk protein yield decreased from 0.47kg/d to 0.30 kg/d, milk fat yield decreased from 0.46kg/d to 0.28kg/d, lactose yield decreased from 0.71kg/d to TP (94.18 + 0.35115.07 + 1.04g/L, p=0.049), globulin and glucose. The content of (2.88 + 0.043.54 + 0.11 mmol/L, p=0.03) increased significantly, and LDL-C (0.18 + 0.030.29 + 0.01mmol/L, p=0.004) and AKT (4.17 + 0.3135.50 + 4.15 U/L, p=0.004) significantly increased; HDL-C significantly decreased (3.23 + 0.04, 0.04, 0.04) and 80.05 + The content of g/mL, p=0.048) increased significantly; the content of cortisol (288.21 + 49.73573.76 + 11.71ng/mL, p=0.009) increased remarkably. The concentration of insulin (22.48 + 2.5325.66 + 1.95IU/L, p=0.057) and glucagon (597.18 + 58.11658.02 + 49.47pg/mL, p=0.06) increased. The results suggested that the cows could induce cows under high temperature and high humidity in summer in Nanjing, China. During heat stress, the endocrine and nutritional metabolism of dairy cows varied, showing the decrease of milk secretion, the decrease of milk quality by.2, the relationship between the change of milk composition precursor redistribution and the decrease of milk quality during heat stress. The relationship between the amino acid and free fatty acids in the blood and milk fat and milk protein synthesis was explored. The possible mechanism of milk quality reduction in lactating cows during heat stress. Experimental animals were fed and treated in the same third chapters. The jugular blood was collected at the beginning and end of the experiment. The contents of free amino acids and free amino acids in the blood were detected by RP-HPLC and ELISA hair respectively. The results showed that with the increase of temperature (from 26 > to the highest 38), milk fat With the decrease of milk protein content, the total NEFA in the blood of the experimental cows increased significantly (178.20 + 16.70272.42 + 20.53 g/mL, p=0.025), and the main carbohydrate amino acids such as Glu, Asp, Gly and Val (811.28 + 259.223254.05 + 666.79 mu mol/L, p=0.035) and Leu, and so on were increased or significantly increased (169.26 + 105.50 105.50 mu. 6) the content of total branched chain amino acids (Val, LLE, Leu) increased significantly (198.36 + 52.571474.85 + 355.83 mu mol/L, p=0.02870.05), and the proportion of the essential amino acids increased from 54.75% to 67.89%. conclusion: in the heat stress state of high temperature dairy cows in summer, the milk fat and milk protein content decreased, but the blood NEFA, free amino acids, especially the branched amino groups. It is suggested that the high levels of NEFA and free amino acids in the blood are not completely used in the synthesis of milk fat and milk protein, but also play other roles, such as energy supply, sugar isogenesis, and immune response. The role of the latter is preceded by the participation of milk fat and the synthesis of milk protein. The redistribution changes may be one of the mechanisms leading to the decrease of milk protein and milk fat,.3, the mechanism of redistribution of milk ingredients precursors caused by heat stress in the first two chapters of the experiment, we found that heat stress can cause heavy distribution of milk protein and milk fat precursors, and cause milk protein and milk fat content in milk. In order to explore the mechanism of milk protein and milk fat precursor redistribution caused by the redistribution of milk ingredients, the experimental dairy cows were collected in this experiment. The Real-time PCR method was used to detect the key enzymes PC and PEPCK in the liver of dairy cows and the GHR, IGFR, HSP70 and Keap1-Nrf2 pathways in the liver tissue and their lower levels. The expression of HO1, GCLM, NQO1, GCLC and other proteins was detected by mRNA expression. The results showed that the expression level of PC (0.917 + 0.0081.08 + 0.025, p=0.045) and PEPCK (0.87 + 0.0091.29 + 0.132, p=0.032) in the liver of dairy cows increased significantly during heat stress, and the expression level of GHR (1.05 + 0.02, 0.02, 0.007) was significantly up-regulated. The expression of HSP70 (0.35 + 0.1651.55 + 0.012, =0.006) was significantly increased in the liver, and the expression of Keap1 (1.07 + 0.241.32 + 0.27, p=0.046) and Nrf2 (1.59 + 0.181.73 + 0.19, p=0.049) increased significantly, and the expression of HOl (0.98 + 0.081.19 + 0.02, p=0.037) and 0.92 + 0.02 (0.92) increased significantly. The expression of GCLC (+ 0.100.97 + 0.05, p=0.059) and GCLC (0.84 + 0.071.29 + 0.11, p=0.061) increased, but the difference was not significant. The results suggested that the glucose and isogenesis and anti stress in the liver were enhanced during heat stress. The milk protein, the milk fat precursor, and the milk fat precursor were more involved in the glucose differentiation under the GH-IGF-I axis and the Keap1-Nrf2-ARE signaling pathway. The process of production and resistance to stress damage of cells, too much consumed the precursors of milk composition, and reduced the synthesis of milk protein and milk fat.
【学位授予单位】：南京农业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：S823

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