| In this study,the heat stress of weaning lambs was evaluated using an environmental control room,and the effect of production performance and rumen flora of lamb was investigated under heat stress.The study included two experiments as follows.Experiment 1:Heat-stress evaluation of weaning lambThe purpose of this study was to evaluate the effects of different heat stress conditions on production performance and physiological parameters in weaned lambs.Using the method of precise temperature-humidity control in environmental chamber,12 healthy weaning lambs with similar weight were randomly divided into two groups,with 6 lambs in each group,and kept in two chambers with the humidity(RH)at 60%and 80%,respectively.The steepest slope test design was adopted,and the ambient temperature(AT)began to rise from 21.5℃,and every 2℃ was a gradient.Each gradient lasted for 3 days and the continued increase of AT was not stopped until the lambs was observed a severe stress,and then the AT was decreased continually to initial AT in same way.The whole experiment lasted for 42 days.The results showed that:(1)The average daily feed intake(ADFI)had different changing trends under two kinds of RH.Under 80%,two AT point of ADFI was observed at 27.5℃ and 33.5℃;under 60%,the AT points was 29.5℃ and 33.5℃.The change of drinking water quantity had a same tendency under two RH,the AT point was 27.5℃ and 33.5℃.(2)Under both RH,rectal temperature increased linearly with the AT increase(P<0.05).The regression equation was as follows:y=0.2314x+33621,R2=0.94(60%);y=0.2299x+33.711,R2=0.92(80%).(3)Under the two RH,body surface temperature and AT presented a linear positive correlation(P<0.05),and the regression equation was as follows:y=0.5543x+16.747,R2=0.96(60%);y=0.4318x+20.763,R2=0.96(80%).(4)Under the two RH,the regression equation of respiration rate and AT was as follows:y=9.5371 x-181.94,R2=0.95(60%);y=14.208x-288.74,R2=0.97(80%).Experiment 2:Production performance,digestibility,and rumen microflora in lambs under heat stressThe production performance,digestion performance,rumen fermentation parameters,and rumen flora were investigated in lambs under heat stress(33.5℃,60%).According to experiment 1,the condition of 33.5℃ and 60%resulted in a significant change in both ADFI and water intake.The lambs were randomly divided into two groups:one group was the control group(21.5℃ and 60%);The other group was the heat stress group(33.5℃ and RH 60%),and the experimental period was 15 days.The results showed that:(1)under heat stress,the ADFI,average daily gain(ADG)and feed weight ratio(F/G)in lambs were reduced(P<0.05).The apparent digestibility of crude protein(CP),Ether extract(EE),neutral detergent fiber(NDF),acid detergent fiber(ADF),and calcium(Ca)decreased compared with the control group(P<0.05),especially NDF digestibility was only 52.9%of the control,and the digestibility of phosphorus was not different(P<0.05)between two groups(P>0.05).(2)Under heat stress,the blood physical-chemical parameters showed a significant change,and the levels of cortisol(COR)and glucose(GLU)increased(P<0.05).In addition,the antioxidant capacity of stressed lambs decreased,and the parameters involved total antioxidant capacity(T-AOC),superoxide dismutase(SOD),and catalase(CAT)were reduced(P<0.05)under heat stress.Also,the levels of heat stress proteins(HSP60,HSP70,and HSP90)in blood were increased(P<0.05).(3)The rumen fermentation parameters and rumen flora structure in stressed lambs were significantly changed,and the concentrations of total volatile fatty acid(TVFA),acetic acid,propionic acid,and butyric acid decreased(P<0.05).From structure of rumen flora,the relative abundance of Prevotellaceae increased(P<0.05)under heat stress.However,the relative abundance of other families(Veillonellaceae、Ruminococcaceae、Bacteroidales_S24-7_group,Coriobacteriaceae,and so on)was reduced(P<0.05).Besides,under heat stress,the Methanobrevibacter in rumen archaea increased(P<0.05),while the Methanosphaera decreased(P<0.05).In rumen fungus,the unidentified genus was higher(P<0.05).The proportion of internal ciliates in rumen protists was reduced(P<0.05),and the proportion of anterior caterpillars was increased(P<0.05).In summary,under the two humidity conditions of 80%and 60%,the average daily feed intake and average daily water consumption of weaning lambs have an obvious turning point with the increase of temperature;in addition,the rectal temperature,body surface temperature and Respiration rate and ambient temperature are linearly positively correlated.Under heat stress conditions,the production performance and digestion performance of weaned lambs are significantly reduced,the antioxidant performance indicators decrease,and the heat stress protein content increase.Heat stress affects the rumen fermentation and flora structure of weaning lambs. |
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