食品科学

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热应激时奶牛血液中游离氨基酸流向与乳蛋白下降的关系研究

艾 阳,曹 洋,谢正露,张源淑*,沈向真   

  1. 南京农业大学 农业部动物生理生化重点开放实验室,江苏 南京 210095
  • 出版日期:2015-06-15 发布日期:2015-06-07

Relationship between Free Amino Acids in Cow’s Blood and Decreasing Milk Protein under Heat Stress

AI Yang, CAO Yang, XIE Zhenglu, ZHANG Yuanshu*, SHEN Xiangzhen   

  1. Key Laboratory of Animal Physiology and Biochemistry, Ministry of Agriculture, Nanjing Agricultural University, Nanjing 210095, China
  • Online:2015-06-15 Published:2015-06-07

摘要:

目的:探讨热应激时奶牛血液中氨基酸与乳蛋白的相互关系。方法:选取6 头相同泌乳期奶牛,正常饲喂和饮水,实验期35 d(6月29日—8月5日)。每日10:00和18:00记录气温,统计产奶量,每周取全天奶样,Foss乳成分分析仪检测乳蛋白含量。于实验开始第1周和最后1 周采集颈静脉血液,反相高效液相色谱法检测血液中游离氨基酸含量。结果:随着气温的升高(由26 ℃升高至最高38 ℃),实验奶牛日均产奶量由15.2 kg/d下降至10 kg/d,乳蛋白产量由0.47 kg/d下降至0.31 kg/d。血液中Glu、Asp、Gly和Val等主要的生糖氨基酸(参与糖异生作用)以及Leu、Ile等生酮氨基酸均升高或显著升高(0.01<P<0.05);总支链氨基酸(Val、Ile、Leu,主要参加免疫反应)含量显著增加(P<0.05),在必需氨基酸中所占的比例由54.75%增至67.89%。结论:在夏季高温高湿条件下,奶牛可发生热应激,产奶量和乳蛋白含量均降低,但血液中游离氨基酸,特别是支链氨基酸含量显著升高。提示热应激时奶牛血液中高水平的游离氨基酸并未完全用于乳蛋白的合成,还发挥了除此之外的其他作用,而后者的作用优先于参与乳蛋白的合成,即可能优先作为功能性氨基酸参与了机体的其他活动。

关键词: 热应激, 泌乳奶牛, 乳, 乳蛋白, 血浆, 游离氨基酸

Abstract:

Heat stress is an unspecific reaction of the body in hot and moist environments. Many studies have demonstrated
that heat stress can be formed at temperature over 22 ℃ or temperature-humidity index higher than 72. In order to explore
the relationship between free amino acids in plasma and milk protein synthesis under heat stress, we selected 6 dairy
cows with similar parturition, regular diet and unlimited drink. The experiment lasted 35 days (from June 29 to August 5).
The temperature (at 10:00 and 18:00) and milk yield were recorded. The protein content in whole-day milk sample was
tested weekly by FOSS milk composition analyzer. Blood samples from jugular vein in both the first and last weeks were
also collected. The free amino acid contents in blood samples were analyzed by RP-HPLC system. Our results showed
that the milk yield decreased from 15.2 to 10 kg/d as the temperature rose from 26 to 38 ℃, while milk protein declined
from 0.47 to 0.31 kg/d. In blood, Glu, Asp, Gly and Val, known as the main amino acids for gluconeogenesis, increased
(0.01 < P < 0.05), so did Leu and Ile, known as the main amino acids for ketogenesis. The branch chain amino acids (Val, Ile
and Leu) responsible for immune response increased significantly. In conclusion, in hot and moist environment, dairy cows were
vulnerable to heat stress, which could cause reduction of milk production and milk protein synthesis, suggesting that the high level
of blood amino acids could preferentially exert other functions besides milk protein synthesis under heat stress.

Key words: heat stress, lactating dairy cows, milk, milk protein, plasma, free amino acids

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