Research Of Cold Stress On The Mechanism Of Oxidative Damage In Laying Hens

The ambient temperature is one of the important environmental factors for laying hensto survive, and low temperature environment cause serious damage in production. Lowambient temperature can stimulate cold stress. On one hand, the cold stress can reduceefficiency of feed utilization, on the other hand, it affect hens’ production state. However,the negative mechanism of cold stress is still unclear. This paper is to speculate injurymechanisms of cold stress mainly from four areas of indicators as body temperature,energy metabolism, mitochondrial proton channel (avUCP, ANT) mRNA and antioxidantsindicators.Experiment1: Select40health commercial Hy-land gray laying hens of40weekswith similar weight and small individual differences in the trial. The average weight of thechickens was1.415Kg. The chickens randomly divided into8groups (Ⅰ, Ⅱ, Ⅲ, Ⅳ, Ⅴ,Ⅵ, Ⅶ, Ⅷ) and5repeat each group. The groupⅠ-Ⅶ was the test group (selecting Ⅰ-Ⅴ as the stress group; Ⅵ, Ⅶ as recovery group), and Ⅷ was the control group. Thetest group Ⅶ and the control group Ⅷ were selected for body temperature test, eachgroups was pretreated in a indoor environment (temperature:21±2℃, relative humidity:76.05±18.59%, the wind speed <0.4m/s) for12h. At the beginning of the experiment,the test groups was quickly transferred outdoor test group of chickens,and experiment ofand the control group Ⅷ started at the same time. Cold stress groups Ⅰ-Ⅴ wereexposed to the cold outdoor environment for2h,4h,6h,8h,10h in order, recoverygroup Ⅵ, Ⅶ quickly transferred to a closed room to restore for2h,4h after coldexposed for10h. The test group the Ⅶ was put outside to undergo the cold environment(temperature:-8.68±2.12℃, relative humidity:75±4%, the wind speed:0.42±0.01m/s)for10h and put back to environment controlled room for restoration for4h. The place wasset at biaoben garden of Hebei Agriculture University in Baoding city, and the coldexposure time was lasted from19:30to next day5:30. Under-wing temperature and rectaltemperature was measured per30min for each hens. The result showed that compared withthe control group cold environment can reduce under-wing temperature and rectaltemperature, the both temperature was elevated and exceeded the control group afterrecovery process.Experiment2: Experimental groups was divided as experiment1, and selected Ⅰ-Ⅴ as stress groups, Ⅵ andⅦ as recovery groups, Ⅷ as the control group. Each groupaccept pretreatment in confined indoor environment for12h, and began at the same time.Cold stress groupⅠ-Ⅴstimulated outdoor for2h,4h,6h,8h,10h orderly. Recoverygroup Ⅵ,Ⅶ accept the same cold exposure for10h as stress group Ⅴand then quicklytransferred to indoor environment for2h,4h. The results showed as followed:(1) thelevel of energy metabolism: Glucose levels increased (P <0.05) and lactate levels decrease(P <0.01) in stress group V; Pyruvic level was elevated (P <0.05) in stress group III, IVand V comparing to control group; lactate/pyruvate ratio was significantly decreased instress group Ⅲ, Ⅳ, Ⅴ (P <0.01), and recovery group Ⅵ comparing to the stress groupⅤ significantly elevated (P <0.01). The serum triglyceride levels of stress group III wasincreased (P <0.01)comparing to recovery group Ⅵ, Ⅶ and control group VIII;recovery group Ⅵ stress group III, IV, compared significantly decreased (P <0.01). Freefatty acid levels in the stress group Ⅲ was increased (P <0.05) comparing with recoverygroup as well as the control group Ⅵ VIII significantly with; stress group III phase for therecovery group VI of free fatty acid content significantly with the increase, and thedifference in a very significant significantly (P <0.01). Serum uric acid level of stressgroup Ⅱ, Ⅲ, Ⅳ, Ⅴ relative to the control group was increased (P <0.01).(2) hormonelevels: Comparing to control group, serum insulin levels of stress group Ⅱ, Ⅲ, Ⅳ, Ⅴand recovery group VI was increased (P <0.05);Stress groupⅠand recovery group werechanged indistinctively (P>0.05). Serum T3levels of the stress group IV relative to thecontrol group was increased (P <0.05); Recovery group Ⅵ relative to the the stress groupⅣ, Ⅴ,the T3levels decreased (P <0.05). Serum T4levels in the stress group Ⅲ, Ⅳ, Ⅴgroup relative to the control group the VIII and recovery group Ⅶ significantly increased(P <0.05). Relative to the control group VIII, the insulin resistance index HOMA-IRIlevels Stress groupⅡ, Ⅲ, Ⅳ, Ⅴ, as well as the recovery group VI were significantlyincreased (P <0.05); Corresponding to the insulin sensitivity index ISI, recovery groupVII,stress group Ⅱ, Ⅲ, IV, Ⅴ, Ⅵ was significantly decreased (P <0.05).Experiment3: Test steps as above. For stress group Ⅴ and recovery group Ⅵ, Ⅶexperimental cold stress environment, avUCP mRNA expressed in the pectoral muscletissue were significantly increased (P <0.05) relative to control group VIII levels, whileothers stress group changes was not significant (P>0.05). Stress group Ⅳ, Ⅴ, recoverygroup Ⅵ,VII relative to the control group, avUCP mRNA expressed in the leg tissue wereincreased (P <0.05). ANT mRNA expression levels in pectoral muscle tissue in all thegroups were no significant difference (P>0.05); However, leg tissue ANT mRNAexpressed in stress group I, III, IV,Ⅴ and recovery group Ⅵ were significantly increased(P <0.05)the relative to the control group level.Experiment4: Test steps as above. From testing the samples, and conclude the resultas follows: Compared to the control group VIII, serum cholinesterase activity in the stress group V and recovery group Ⅵ, Ⅶwas decreased (P <0.05). Creatine kinase activity instress group Ⅲ,Ⅳ,Ⅴ were significantly higher (P <0.05) than the control group; creatinekinase activity in recovery group Ⅶ relative to the other group increased significantly (P<0.05). In the cold stress process and the recovery process, lactate dehydrogenase and γ-glutamic acid peptidase activity had no significant change (P>0.05).Low temperature environment, hepatic GSH-PX levels in stress group II weresignificantly increased (P <0.05) relative to the control group VIII and recovery group VII.Hepatic T-SOD activity in the stress group Ⅴ, Ⅵ was higher (P <0.05) than controlgroup VIII and stress group Ⅰ. In the cold stress process and the recovery process,T-AOC and MDA had no significant change (P>0.05).Recovery groupⅥ nephritic T-AOC was significantly higher (P <0.05) than thecontrol group VIII; T-AOC did not change significantly in the stress groups (P>0.05).Comparing with stress group Ⅰ,control group VIII and recovery group Ⅶ,recovery groupⅥ nephritic T-SOD activity increased significantly elevated (P <0.05). GSH-PX activityand MDA content in the nephritic samples was not significant changed (P>0.05).Stress group IV level was higher (P <0.05) than the stress group Ⅰ, Ⅱ, Ⅲ andrecovery group VI, Ⅶ. To recovery group Ⅵ, pancreatic T-AOC was significantlyreduced (P <0.05) relative to stress group IV and Ⅴ. The pancreas GSH-PX in stressgroup Ⅱ, Ⅲ and recovery group were significantly decreased (P <0.05) relative to thestress group Ⅰ. Stress group Ⅰ MDA levels was higher (P <0.05) than control groupVIII and stress group III. T-SOD activity showed indifferent (P>0.05) in the pancreasduring the test.Relative to the control group VIII, the stress group III, Ⅴ, Ⅵ T-AOC wassignificantly increased (P <0.05) in the skeletal muscle. The stress group Ⅳ, Ⅴ andrecovery group VI, VII, show a lower GSH-PX level (P <0.05) than stress the group Ⅱ.The stress group Ⅱ GSH-PX activity was elevated (P <0.05) relative to the control groupⅧ. T-SOD activity in stress group IV was significantly increased (P <0.05) relative tostress the group Ⅰin muscle tissue; compared with the stress group IV, T-SOD activity inthe stress group V and recovery group VI,Ⅶ significantly reduced (P <0.05); comparedwith the control group VIII, T-SOD activity in recovery group VII was significantlyreduced(P <0.05). MDA in recovery group Ⅵ,VII relative to stress groupⅠand the controlgroup was significantly decreased (P <0.05) in the skeletal muscle.