Effect Of Acute Heat Exposure On The Growth Performance And Melanin Synthesis Of Taihe Silky Fowls

The objective of this study was to investigate the effect of acute heat exposure ongrowth performance, antioxidant abilities and melanin synthesis of Taihe silky fowls. Atotal of14442-day-old Taihe silky fowls were randomly divided into two groups:thermoneutral temperature control group and acute heat exposure group, each group hadfour replicates and each replicate contains18chickens. At8:00AM when the chickenswere at45days of age, the ambient temperature of acute heat exposure group wassuddenly increased from thermoneutral temperature to37℃and the chickens wereexposed to heat stress for24h, and then the chickens were transferred to thermoneutralconditions. During the trail, the thermoneutral temperature of control group wasmaintained at22～24℃.On d1,7,14and21after acute heat exposure treatment, bodyweight and feed intake of trail chickens of each replicate were recorded respectively. Twochickens were selected from each replicate at0h,12h,24h during acute heat exposureand24h,6d,20d post heat exposure, blood samples were collected from the wing vein,and then killed and the skins, pectoralis muscles, livers, kidneys and hypothalamussamples were immediately collected. The antioxidant abilities, the contents ofα-melanocyte stimulating hormone (α-MSH) and Cyclic Adenosine monophosphate(cAMP)，expressions of melanin biosynthesis-related genes and total melanin contentswere determined. The results showed as follows:(1) There were no significant effects of acute heat exposure on the average dailyweight gain and average daily feed intake and feed gain ratio of Taihe silky fowls after theambient temperature was recovered to thermoneutral conditions.(2) Acute heat exposure resulted in heat stress effect to a certain extent in Taihe silkyfowls. An obvious lipid peroxidation was observed in the pectoralis muscle and lipidperoxidation also occurred in serum, skin, liver, kidney of Taihe silky fowls to a certainextent. Acute heat exposure decreased the antioxidant abilities in serum, skin and pectoralismuscle of Taihe silky fowls to a certain extent, whereas no significant change inantioxidant abilities in liver and kidney was observed.(3) Acute heat exposure tended to decrease the total melanin contents in skins andpectoralis muscles of Taihe silky fowls. There were no significant effects of acute heatexposure on the total melanin contents in livers of Taihe silky fowls.(4) Acute heat exposure resulted in increasing tendencies in the contents of α-MSH inserums and hypothalamus, the contents of cAMP in tissues and the expressions ofmelanocortin1receptor (MC1R) mRNA in tissues of Taihe silky fowls. Acute heatexposure tended to increase the expressions of tyrosinase-related protein (TYR),tyrosinase-related proteins1(TYRP1) and tyrosinase-related proteins2(TYRP2) mRNAof Taihe silky fowls exposed to acute heat exposure. (5) Acute heat exposure for24h caused no significant effects on the antioxidantabilities, total melanin contents, expressions of melanin biosyntheis-related genes (TYR,TYRP1, TYRP2, MC1R), the contents of α-MSH in serums and hypothalamus and thecontents of cAMP in tissues of Taihe silky folws24h post heat exposure when the ambienttemperature was recovered to thermoneutral conditions.In summary, acute heat exposure tended to decrease the antioxidant abilities and thetotal melanin contents of Taihe silky fowls. But acute heat exposure for24h caused nosignificant effects on the growth performance and melanin synthesis of Taihe silky fowls24h post heat exposure when the ambient temperature was recovered to thermoneutralconditions.