Evaluations Of Thermal Comfort Status Based On The Body Temperature And Respiratory Rate Of Broilers

Heat stress has detrimental effects on the health and performance of poultry,resulting in huge economic losses.Rational regulating the temperature in poultry house can effectively alleviate the adverse effects of heat stress.In the present paper,we studied the changes in body temperature and respiratory rate of broilers with increasing ambient environment,and analyzed the inflection point temperature（IPT,the ambient temperature above which the body temperature and the respiratory rate begin to increase）.By this way,we can determined the ambient temperature range of broilers in different thermal comfort conditions,and can provide a basis for guiding the regulation of temperature in the chicken house.In the present paper,we conducted three experiments to respectively measure the changes of body surface temperature（ST）,core temperature（CT）and respiratory rate（RR）of broilers with increasing ambient temperature（AT）.Each experiment has two section.In section 1,ten AA broilers at 21 days old were raised in a controlled climate chamber.The AT in the chamber was increased gradually by one degree per 0.5 h from 18°C to 35°C.The ST and CT of broilers were measured by the miniature temperature recorders,an infrared video recorder was used to record the respiratory rate of broilers.The IPTs of ST,CT,and RR were analyzed using a nonlinear regression model.The measurements were repeated for 3 days to study the individual variation and the parallelism of the 3 IPT measurements.In section 2,150 AA broilers were reared from 1 day old on a standard corn–soybean meal diet.At 21,28,35,42,and 49 days of age,30 were selected and raised in two controlled climate chambers.The relative humidity in the chambers were fixed at 50%and 80%respectively.The AT in chambers were setting as same as section 1.The IPTs were analyzed as same as section1.The results of the study were as follows:The ST,CT,and RR of broilers were changed with increasing AT as an obvious broken-linear model.The IPT can be analyzed used the non-linear regression model.The parallelism of IPTst,IPTct,and IPT_RRobtained from the three-day repeated experiment was good,and the coefficients of variation of the three-day measurement results were 0.62°C,0.90°C,and 0.21°C,respectively;The variation between individuals was large,and the individual coefficients of variation of the three indicators were between 1.35-1.65°C,2.75-2.82°C,and 0.98-1.16°C,respectively.The IPTst,IPTct,IPT_RRof broilers were significantly decreased with increasing age（P<0.001）.At50%RH,IPTst was 24.68,23.61,23.03,22.67,and 22.01°C;IPTct was 27.77,26.87,25.01,24.32,and23.76°C;and IPT_RRwas 31.45,30.48,28.40,27.71,and 26.27°C in 21-49 broilers,respectively.Humidity significantly affected IPTst（P=0.043）,IPTct（P=0.017）,and IPT_RR（P<0.001）.High humidity（80%RH）decreased IPTst by 0.40℃on average,IPTct by 0.55℃,and IPT_RRby 1.02℃.The temperature-humidity index（THI）models of broilers at different ages were estimated based on the variations of ST:THI_d21=0.94T_db+0.06T_wb;THI_d28=0.82T_db+0.18T_wb;THI_d35=0.69T_db+0.31T_wb;THI_d42=0.67T_db+0.33T_wb;THI_d49=0.61 T_db+0.39T_wb.According to the definition of thermal neutral zone by IUPS,the ambient temperature above which the sensible heat loss of broilers begins to increase is the upper limit temperature of the thermal comfort zone,and the ambient temperature above which the evaporative heat loss of broilers begins to increase is the upper limit temperature of the thermal neutral zone.The change of ST can represent the change in sensible heat loss.Therefore,IPTst is the upper limit temperature of the thermal comfort zone of broilers.However the IPT_RRis higher than IPTct,indicating that the respiratory rate is not suitable for the assessment of the upper limit temperature of the thermal neutral zone.It is speculated that at relatively low ambient temperatures,broilers have begun to increase the evaporative heat loss of the skin by increasing the skin temperature.In summary,the upper limit temperature of the thermal comfort zone of broilers can be estimated by measuring the changes of ST of broilers with increasing ambient temperature and analyzing the IPTst.The method has good repeatability.The comfortable temperature of 21-49 days old broilers（at 50%RH）should be slightly lower than or equal to 24.7,23.6,23,22.7 and 22℃,respectively（decreased by 0.4℃at 80%RH）.The temperature in the 21-49 days old broiler house（50%RH）should not exceed 27.8,26.9,25,24.3,and 23.8°C（decreased by 0.5℃at 80%RH）.