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Effects Of Thermal Environment And Individual Heat Sensitivity On Milk Production Performance And Physiological Stress Indicators Of Dairy Cows

Posted on:2019-03-26Degree:MasterType:Thesis
Country:ChinaCandidate:D D PengFull Text:PDF
GTID:2393330545980307Subject:Breeding
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This paper consists of two experiments.In experiment one,we studied the changing rules of rectal temperature(RT),respiratory rate(RR)and body surface temperature(BST)of dairy cows under different temperature humidity index(THI)conditions.Productive multiparous cows during the peak milk production period were chosen as experimental animals.The RT,RR and BST were regularly measured simultaneously under high(THI>78),moderate(72?THI?78)and low(THI<72)THI conditions.The Infrared Thermal Imager(IRT)was used to measure BST,including different areas in left side such as eye area,ear area,cheek,forehead,flank,rump,fore udder and rear udder.All the measurements were performed 14 times in high(six times),moderate(three times)and low(five times)THI conditions,with a total of 488 cows.The results showed that:(1)RT and RR were significantly different under different THI conditions(P<0.01),and they began to increase rapidly when THI were 74.1 and 73.5,respectively.(2)Various areas of BST were significantly affected under different THI conditions(P<0.01).The mean and maximum forehead temperature varied the most among all measured areas,being 2.80 and 2.22 ?,respectively,and they began to increase rapidly when THI were 71.4 and 66.8,respectively.(3)The BST of all areas were positively correlated with THI and RT(P<0.01).The correlation coefficients were the highest in terms of mean and maximum forehead temperatures with THI(0.808 and 0.740,respectively),and with RT(0.557 and 0.504,respectively).While ear,cheek,flank and rump temperatures showed relatively high coefficients with THI and RT;eye,fore udder and rear udder temperatures showed lower coefficients.(4)There were significant correlations among BST of different regions(P<0.01),most of which were above 0.68.The BST of ear area and cheek,rump and flank had the highest correlation coefficients(r=0.889,0.902).In experiment two,the changing rules of milk production,milk composition,RT,RR,BST and stress hormones of high and low heat sensitivity cows were studied under different THI conditions.Nineteen cows with high heat sensitivity and Twenty-two cows with low heat sensitivity were selected respectively,according to the breathing score in high temperature environment.No differences were observed between the two groups in terms of parity,milk yield and days in milk.RT,RR and BST of experimental cows were measured 11 times under high(five times),moderate(three times)and low(three times)THI conditions.Blood and milk samples were collected once to detect the content of stress hormones and milk composition under high,moderate and low THI conditions,respectively.The results showed that:(1)Milk protein rate and fat rate were different under different THI conditions(P<0.05).Milk fat rate of high heat sensitivity cows was significantly higher than that of low heat sensitivity cows.There was no interaction between THI and heat sensitivity on milk composition(P>0.05).(2)RT,RR were significantly different under different THI conditions(P<0.01),in which the RT,RR of high sensitivity cows were higher than that of low sensitivity cows(P<0.05).For each unit of THI that increased,the RT of high and low sensitivity cows increased 0.07 and 0.05 ?,and RR increased 2.75 and 2.09 breaths per minute,respectively.There were significant interactions between THI and heat sensitivity on RT and RR(P<0.05).(3)BST were significantly different under different THI conditions(P<0.01),of which the rump and rear udder temperature of high sensitivity cows were higher than that of low sensitivity cows.There was a significant interaction between THI and heat sensitivity on ear temperature(P<0.05).(4)With the increasing of THI,the content of Triiodothyronine(T3)and Tetraiodothyronine(T4)in plasma and milk were significantly decreased(P<0.01),while the content of Cortisol(COR)was significantly increased(P<0.01).The differences of T3,T4 and COR content in plasma and milk between high and low sensitivity cows were not significant(P>0.05).There was significant interaction between THI and heat sensitivity on plasma T4 content(P<0.05).(5)Plasma T4 and COR were significantly correlated with milk T4 and COR(P<0.01),of which the correlation between plasma T4 and milk T4 was higher(r=0.414).In conclusion,(1)the correlation coefficients of the mean and maximum forehead temperature with THI and RT were the highest.The THI conditions where mean and maximum forehead temperatures started to increase quickly(71.4 and 66.8)were lower than that where RT and RR started to increase quickly(74.1,73.5).Thus,we concluded that the forehead is the most optimum region for early assessing the heat stress reflecting RT by using IRT.(2)THI had significant effects on milk composition,RT,RR,BST,T3,T4,and COR content of high and low heat sensitivity cows.The milk fat rate,RT,RR,rump and fore udder temperature of high heat sensitivity cows were all significantly higher than that of low heat sensitivity cows.Thus,we concluded that high heat sensitivity cows have lower heat tolerance than low heat sensitivity cows,indicating that the breathing score have a certain reference value in breeding thermo resistant dairy cows.This finding provide a scientific basis for the better management of different heat resistant herds.
Keywords/Search Tags:Heat stress, Temperature humidity index, Rectal temperature, Respiratory rate, Body surface temperature
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