| With Arbor Acres broilers and Jining hundred-day chickens as the experimental materials,the present study tested adaptive responses of chickens to high ambient temperatures to identify suitable indicators for selection of heat-tolerant individuals on the one hand, and compared the expression difference of thermoregulatory behaviors and thermal stress-related genes between heat-resistant and heat-sensitive chickens to clarify the mechanism of heat tolerance on the other hand.Study 1 included 2 trials. In trial 1, 16-day-old Arbor Acres broilers(n = 30) with similar body weights were raised in a room with a temperature at 33±0.5oC(50% of relative humidity). Rectal temperature(RT) was measured on each bird at 0, 6, 12 and 24 h, and blood samples were collected at 0 and 24 h to analyze the composition. Thereafter the ambient temperature was increased to 36±1oC to kill all the chickens, and survival time(HSST) was recorded for each individual. The gap between the RT or blood variables and initial values was calculated. A negative correlation(P < 0.05) was found between HSST and the interval of total number of leucocytes(R2 =-0.45), lymphocyte count(R2 =-0.44), or hematokrit(R2 =-0.45). In trial 2, 42-day-old Arbor Acres broilers(n = 30) with similar body weights were kept in a climate chamber at 36±1oC for 6 hours, after which the temperature was reduced to25±0.5oC. Following this, the birds were divided into 2 groups: those surviving the heat shock and those dying within 24 hours after the heat shock. Before(0 h) and after(6 h) heat shock,RT was measured and blood samples were taken. Surviving broilers had a higher variability of RT(P < 0.01), Plasma urate(P = 0.04) and lymphocyte ratio(P < 0.01), and a lower rangeability of Plasma glucose(P = 0.04), intermediate cell rate(P = 0.01) and granulocyte rate(P = 0.04) than did non-surviving chickens.Study 2 had also 2 trials. In trial 1, 74-day-old Jining hundred-day chickens(n = 30) with similar body weights were raised in a room with a temperature at 33±0.5oC(50% of relative humidity). Rectal temperature was measured on each bird at 0, 6, 12 and 24 h, and bloodsamples were collected at 0 and 24 h to analyze the composition. Thereafter the ambient temperature was increased to 40±1oC to kill all the chickens, and HSST was recorded for each individual. The gap between the RT or blood variables and initial values was calculated.Results showed that HSST was positively(P < 0.05) correlated with the interval of RT(R2 =0.39, 6 h; R2 = 0.40, 12 h) and granulocyte rate(R2 = 0.41, 24 h), and negatively related to that of the mean corpuscular volume(R2 =-0.48, P < 0.01). In trial 2, 84-day-old Jining hundred-day chickens(n = 30) with similar body weights were kept in a climate chamber at40±1oC for 8 hours, after which the temperature was reduced to 25±0.5oC. Following this, the birds were divided into 2 groups: those surviving the heat shock and those dying within 24 hours after the heat shock. Before(0 h) and after(6 h) heat shock, RT was measured and blood samples were taken. Surviving birds had a higher variability of RT and a lower rangeability of granulocyte rate(P < 0.01) than did non-surviving chickens.In study 3, 28-week-old Jining hundred-day chickens with similar performance(about1.21 kg of body weight and 70% laying rate), were housed individually in a temperature-controlled chambers with a photoperiod of 18 hours for 14 days, where they were exposed to a ambient temperature of 35 °C for 6 hours Per day(from 10:00 to 16:00), and the relative humidity was maintained at 50%. Based on the Performance responses in combination with heat tolerance-related indices(the varied range of RT and granulocyte rate)established in study 1 and 2, the birds were divided into 2 groups: those resistant to heat and those sensitive to heat. The expression differences of thermoregulatory behaviors and thermal stress-related genes were compared between them. The drinking frequency was significantly higher(P < 0.01) in heat-resistant chickens than in-sensitive ones. Compared to the heat-sensitive birds, those resistant to heat had a lower(P < 0.01) m RNA abundance of heat shock protein 70(HSP70; heart and kidney) and 90(HSP90; lung and kidney). This was consistent with the gene ex Pression of heat shock transcription factor 3(HSF3; kidney, P =0.01), but was contrary to that of HSF1(heart, P < 0.01).Compared to the heat-sensitive birds,those resistant to heat had a lower(P < 0.01) m RNA abundance of TRPV2( P < 0.01) and TRPV3(P = 0.02).In conclusion, the extent of variability on RT(6-12 h) and granulocyte rate(8-24 h)under mild heat stress might be considered as a reliable indicator for evaluation of heattolerance in chickens.The heat tolerance of the chicken is regulated by the transient receptor potential(TRP) ion channel protein in the hypothalamus, which is related to the drinking behavior, which can be reflected by the stress reaction factors such as HSPs and HSFs. |
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