| The experiments were conducted to evaluate the effect of chronic heat stress on growth performance,nutrient availability and cationic amino acid transporter gene expression of jejunum in yellow-feathered broilers.160 fourteen-day old yellow-feathered broilers were selected for 7-day adaptation,and conducted to do the experiment from 21 to35-day old.The broilers were randomly assigned to 4 groups(with 5 replicates in each group and each replicate contained 8 broilers).(1)Control group A treated with temperature at 26℃(2)Cyclic heat stress group B treated with temperature at 30℃from 10:00 to 16:00,and 26℃from 16:00 to tomorrow 10:00;(3)Cyclic heat stress group C treated with temperature at 34℃from 10:00 to 16:00,and 26℃from 16:00 to tomorrow 10:00;(4)Cyclic heat stress group D treated with temperature at 38℃from 10:00 to 16:00,and 26℃from 16:00 to tomorrow 10:00.Before the experiments were finished,fecal samples were collected for 3 days to determine the utilization of dry matter,crude protein and crude fat by the method of exogenous indicator.O n 35-day old,2 broilers were selected from replicatestodeterminegrowthperformanceandrectumtemperature.Moreover,serum,chyme and tissue of intestine were collected to separately determinate corticosterone of serum,protease activity of jejunum and the expressions of rBAT,CAT1and y~+LAT2 gene for real time-PCR in jejunum.The results showed as follows:(1)Compared with control group A,the average daily gain of cyclic heat stress group B,C and D were reduced by 8.7%,13.0%and 17.6%(P<0.05),average daily feed intake were reduced by 5.7%,11.8%and 12.7%(P<0.05).Compared with control group A,feed conversion ratio of cyclic heat stress group B and C were decreased by 3.4%and 1.5%with no significant(P>0.05),while cyclic heat stress group D was decreased by 6.3%(P<0.05)than that of the control group A.(2)Compared with control group A,the crude fat utilization of cyclic heat stress group B,C and D were reduced by 7.1%,7.3%and 10.2%(P<0.05).The utilization of crude protein in cyclic heat stress group C and D were decreased by 6.0%and 10.3%(P<0.05),while cyclic heat stress group B had no significant difference(P>0.05).(3)Compared with control group A,trypsin activity of jejunum in c yclic heat stress group B and C were reduced by 19.6%,33%and 38.3%(P<0.05);Compared with control group A,chymotrypsin activity of cyclic heat stress group B and C were reduced by 23.8%(P>0.05)and 39.2%(P=0.058),cyclic heat stress group D was decreased by 54.9%(P<0.05).(4)Compared with control group A,phenylalanine and lysine ileal apparent digestibility of cyclic heat stress group C was reduced by 14.2%and 16.1%(P<0.05),histidine,threonine,phenylalanine and lysine ileal apparent digestibility o f cyclic heat stress group D was decreased respectively by 17.6%,20.6%,15.6%and 16.9%(P<0.05),while cyclic heat stress group B had no obvious difference(P>0.05).(5)Compared with control group A,the expressions of r BAT,CAT1 and y~+LAT2 gene in jejunum were reduced markedly by 72.9%,98.4%and 78.7%(P<0.05).From the above,chronic heat stress led to a curb of growth,a decline in feed intake and daily gain;and growth performance of yellow-feathered broilers showed more obvious inhibition with temperature rise.Protease activity(trypsin and chymotrypsin)of jejunum was declined under the chronic heat stress(high temperature)conditions,which made the utilization of crude protein,crude fat,some amino acids apparent digestibility and expressions of r BAT,C AT1 and y~+LAT2 gene in jejunum significantly decreased,which affected digestion and absorption of protein in heat stress. |
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