| Cow heat stress will not only seriously reduce the production performance,reproductive capacity and milk quality of dairy cows,but also endanger the health of dairy cows,greatly reducing the economic benefits of dairy farming.The underlying mechanism of heat stress is still unclear,because the factors that cause heat stress and the complexity of the physiological stage of cows make the mechanism research more complicated,so the study of heat stress needs a deeper and more diverse perspective come explore systematically.Previous study found that micro RNAs(mi RNAs)play an important role in regulating animal cell proliferation,differentiation,apoptosis and anti-oxidative stress,organ damage,growth and reproductive performance,and body immunity during heat stress.In this paper,we studied the physiological indicators,blood biochemical indicators,maintenance behaviors of Chinese Holstein cows in Wuhan area under heat stress(HS)and non-heat stress(NHS)status,and study the mi RNAs in the peripheral blood of dairy cows by high-throughput sequencing.Changes in the expression profile of the animal;explore the effects of heat stress on dairy cows from the system of the cow's macroscopic performance(physiological and behavioral indicators)and microscopic regulation mechanism(biochemical indicators mi RNAs).It provides data and theoretical basis for the research on the heat stress the regulation mechanism of Holstein cows,lays the foundation for revealing the specific mechanism of the temperature stress of the cow's body at the mi RNAs level,and has important practical significance for the improvement of the cow's stress resistance and adaptation to the environment.This experiment divided into two stages: spring(NHS)and summer(HS).A total of 16 mid-lactating Holstein cows with good body condition,similar body weight,1 to 3 parity,and the same feeding and management selected as the research object.They randomly divided into two groups,and the peripheral blood of the cows collected as the test material.At the same time,the physiological indexes,blood biochemical indexes and maintenance behaviors of the test cows in spring and summer were surveyed respectively(n=15),and high-throughput sequencing of mi RNAs in peripheral blood was conducted to explore the regulatory role of differential mi RNAs in heat stress of dairy cows.The main findings were as follows:(1)Under heat stress,the respiratory rate(RR)and rectal temperature(RT)increased significantly(P<0.01).Regardless of whether they were measured as four time periods or daily averages,the RR and RT in the heat stress group were significantly higher than the non-stress group(P<0.01).The daily average RR and daily average RT of HS and NHS cows were 78 times/minute,49 times/minute and 39.5?,38.7 ?respectively.(2)Under heat stress,routine blood tests showed that the number of white blood cells and lymphocytes in the HS group were significantly lower than NHS group(P<0.05).Proinflammatory factors IL-2,IL-6 and TNF-? in plasma both were significantly increased(P<0.05).Antioxidant enzymes GSH-Px and SOD were significantly decreased(P<0.05),and the final oxidation product MDA was significantly increased(P<0.05).The evidence shows that the immune function and antioxidant capacity decreased in heat stress dairy cows.(3)The results of dairy cow maintenance behavior survey showed that compared with cows in the NHS group,the lying time and feeding time of the cows in the HS group were significantly reduced(P<0.05),and the rumination time was significantly reduced(P<0.01).The standing time,the frequency of drinking water and excretion were significantly higher than that of non-heat-stressed cows(P<0.05),and the frequency of urination was significantly higher than that of non-heat-stressed cows(P<0.01).This shows that the maintenance behavior of cows under heat stress is significantly affected.(4)After high-throughput sequencing of mi RNAs in the peripheral blood of dairy cows.Total 629 of mi RNAs identified from the NHS group and the HS group,which 363 known and 266 newly predicted.96 mi RNAs of differentially expressed were screened from the NHS group and the HS group,39 of which were up-regulated and 57 were down-regulated;211 HS and NHS co-expressed mi RNAs,93 specifically expressed in the HS group,and 48 specifically expressed in the NHS group;96 differential mi RNAs were targeted Gene prediction,total 13,836 target genes were predicted.Then target gene GO enrichment analysis and KEGG functional annotation analysis were performed.The results showed that the target genes of these differential mi RNAs mainly enriched in cellular components,and were involved in immunity,endocrine and metabolism,Signal transmission and other processes.In Summary,we found that for the physiological indexes,blood immunity and antioxidant indexes,and maintenance behaviors of lactating dairy cows under heat stress have all changed significantly,resulting in a reduction in the immune function and antioxidant capacity of the dairy cows.The expression profile of mi RNAs in the peripheral blood of dairy cows revealed that the differentially expressed mi RNAs maybe involved in the immune,metabolic,signal transduction and endocrine processes of dairy cows under heat stress. |
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