Comparison Of Physiological Traits And Environmental Adaption To Acute Heat Stress Between Two Chicken Breeds

Muscle development is a complicated reaction of metabolic and physiological effects involving genetic regulation and environmental factors.Temperature stress results in both the welfare and productivity of livestock.With an alarming incidence of global warming,especially in tropical areas,high environmental temperature is expected.Broiler chickens exposed to high environmental stress causes detrimental effects on their skeletal muscle development,immune capability,and productivity.The summer and fall in Zhanjiang in the Guangdong province of China,gives a natural hot and humid climates,respectively,for this study.Using variable morphological identity and adaptive behaviours,two local Chinese strains viz.Kirin chicken(KC)and Guangxi Yellow Chicken(TYC),were investigated to ascertain the effects acute heat stress(AHS)have on their skeletal muscle development and regulatory factors such as heat shock proteins(HSP70,HSP90,HSP110),cytokine genes(IL-1?,IL-6,IL-10),and muscle development genes(MSTN,MyHC,PCNA,and IGF-1)A completely randomised design with a 2 × 2 factorial arrangement involving the two strains(TYC and KC)and two temperature groups(average temperature(control)=30±1?;and AHS=35±1? for 8-h with 70%humidity)was used.The daily ambient temperature and relative humidity fluctuations and adaptive characteristics of broiler breeds were recorded.At age 56 days,the temperatures of the comb(CT),feet(FT),eyelid(ET),and rectal(RT)from each group were taken thrice at 0,2,4,and 8-h AHS,as well as 1,and 3 h recovery.The liver,spleen,breast muscle,and leg muscle samples were collected after 8-h AHS for histopathological examination and gene expression.At age 80 days,the slaughter performance was also analysed.The mean minimum and maximum daily temperatures throughout the study were 27.5?and 33.5?,respectively.The KC possesses both phenotypic and well adaptive traits such as their frizzled feather type,scarce feathers on their body,indicating its high adaptability for high-temperature.The CT and ET of the AHS groups increased while the FT of both strains was not affected during the 8-h trial.The RT of the two strains decreased significantly at 4-hr but increased at the 8-h in the TYC group.All temperatures dropped in the heat-stressed chicken of both breeds during the recovery period.The liver HSP70 was significantly different in the AHS and control group of the KC breed(P<0.05),whereas that of the TYC had no significant difference(P>0.05).HSP90 did not significantly differ(P>0.05)between the AHS and control group of both strains in the liver.However,the expression of HSP110 was significantly different in the AHS and control group of the KC breed(P<0.05),whereas that of the TYC had no significant difference(P>0.05).Spleen mRNA expression of HSP(70,90,and 110)had no significant differences in the AHS and control groups in both strains.IL-1?,IL-6,and IL-10 did not differ significantly in the AHS group and control group in both strains.The histopathological examinations revealed tissue injury in the AHS groups of both strains,with the TYC strain experiencing the severest of injury.The mRNA expression of liver IGF-1 was significantly lower in the AHS group of TYC than the control group(P<0.05),whereas the spleen IGF-1 was significantly lower in the AHS group of KC than the control group(P<0.05).IGF-1 mRNA expression in the breast muscle and leg muscle did not differ significantly in the AHS group and the control group of both strains.The mRNA expression of MSTN in the breast muscle did not differ significantly in the AHS group and the control group of the TYC but lowly expressed in the AHS group than the control of the KC(P<0.05).There was no significant difference in mRNA expression of MSTN in the leg muscle in both TYC and KC.The mRNA expression of MyHC and PCNA in the breast and leg muscle did not differ considerably in the AHS group and the control group of both strains.The final live weight and carcass weight showed a significant enhancement in the treatments(P<0.01 and P<0.05,respectively)and strain × treatment interaction(P<0.05)at 80 days.The breast muscle rate was significantly reduced by heat stress among the treatment(P<0.01).There was no significant difference in the leg muscle rate,liver rate,and spleen rate.In conclusion,AHS could influence physiological,molecular,and immune response,which reduces muscle yield in broiler chicken.Likewise,the differential response to heat stress showed that the Kirin chicken has a better thermal tolerance than the three Guangxi yellow chicken.