One-day old chicks were randomly distributed into acute heat stress (AHS) or persistent heat stress (PHS) groups. Each group was further divided into control (CK), and three AHS ages (1, 2,or 3 weeks of age) experimental subgroups. The chicks in AHS subgroups were submitted to acute heat stress (40 o C for two hours between 12:00 and 14:00 hours during the weekend) and the effects of heat stress on several daily behaviors were observed. At 8 days of age, the chicks of PHS subgroups were submitted to heat stress (40 o C daily). The heat treatment ceased during the weekends and the effects on the behavior were observed three times daily for three consecutive days. The results showed that, compared with the CK group, the duration and frequency of drinking and lying-down behaviors of the AHS birds increased, whereas the duration of feeding and standing significantly decreased (p<0.01). The time spent walking by PHS birds was significantly longer than that of the CK groups (p<0.01), and drinking was also significantly longer than that of the CK group and was significantly different when birds were three weeks old (p=0.05). When heat stress lasted for two and three weeks in PHS group, the duration of lying down was longer compared with the CK group; however, this behavior was significantly shorter than the CK group when birds were three weeks old (p<0.05). These results indicate that heat stress significantly affects the daily behavior of broilers, including feeding, drinking, lying, standing, and walking.
We investigated the effect of heat stress (HS) on the expression of the GABA receptor in the hypothalamic-pituitary-gonadal (HPG) axis of Wenchang chickens. Real-time quantitative RT-PCR (qRT-PCR) was used to quantify the GABA receptor mRNA levels along the HPG axis of chickens under HS (40±0.5 °C) for 1-6 weeks. Our results showed that the expression of GABA A and GABA B receptor at the mRNAs levels in the tissues of HPG axis exhibited fluctuation and variability. After HS, the mRNA level of GABA A receptor was significantly reduced in the hypothalamus of 1-week-old and in the pituitary of 3-week-old chickens, but significantly increased in the pituitary of 1-, 4-, and 5-weekold chickens. The GABA B receptor mRNA level significantly declined in the hypothalamus of 1-week-old and in the pituitary of 3-week-old chickens, but was significantly upregulated in the pituitary and testis of 1-and 2-week-old chickens. At other time points, the expressions of GABA A receptor and GABA B receptor showed no significant differences compared with control group. These results indicated that the levels of GABA A receptor and GABA B receptor mRNAs varied in different tissues of the HPG axis in chickens of different ages, displaying temporal and spatial variations. GABA receptor behaved as a positively-regulated gene by HS, i.e., its mRNA was increased by HS; similarly, it was a negativelyregulated gene by HS, when its expression was reduced by HS.
The regulatory roles of mitogen-activated protein kinase ( MAPK ) signaling pathways on the hypothalamic−pituitary−gonadal axis ( HPG axis ) of Wenchang chicks under heat stress ( HS ) were investigated. Additionally, the crosstalk between these signaling pathways was explored. Immunohistochemical experiments and Western blotting were employed to quantify extracellular regulated protein kinases ( ERK ), c-Jun N-terminal kinases ( JNK ), and p38MAPK ( P38 ). In female chicks, hypothalamic ERKs were upregulated in Weeks 1 and 2 in the HS group compared with the control group ( CK ), while JNK and p38 were downregulated ( P < 0.05). Pituitary MAPKs were all downregulated in the HS group compared with the CK group in Week 3, but p38 was upregulated in Week 4 ( P < 0.01). In the HS group, ovarian MAPKs were all upregulated compared with the CK group during Week 5, whereas ERK was downregulated in Week 6 ( P < 0.01). In contrast to the patterns of MAPK expression in female chicks in the HS and CK groups, ERK in male chicks showed a completely opposite pattern in Weeks 1, 2, and 5, while p38 and JNK were downregulated in both female and male chicks under HS during Weeks 2 and 3. In the HS group, pituitary and testis MAPKs showed a pattern opposite to that observed in female chicks under HS in Week 5; MAPKs were all downregulated ( P < 0.05). Thus, there are gender differences in the MAPK signaling pathways in the HPG axis in chicks, and these pathways showed plasticity. Early HS can enhance chick growth and development as well as promote developing in the MAPK signaling pathways in the HPG axis. However, after heated brooding was discontinued in chicks, long-term HS obstructed chick development and caused tissue and function injury to the HPG axis.
In this study, immunohistochemistry and real-time fluorescent-based quantitative PCR were used to evaluate the expression of heat shock protein (HSP) 60, HSP70, and HSP90 in the small intestine of Wenchang chicks. Compared with the control group (CK), the positive expression of HSP60 and HSP60 mRNA in the heat stress group (HS) were initially higher and subsequently lower in the duodenum (p<0.01). In the HS jejunum, the levels of HSP60 were higher (p<0.01) and the HSP60 mRNA was lower (p<0.05). Whereas the levels of HSP60 in the HS ileum were higher (p<0.05) and then lower (p<0.01), and the HSP60 mRNA was higher (p<0.01). The levels of HSP70 were higher (p<0.01) and the HSP70 mRNA was lower in the duodenum (p<0.05), while the expression of both HSP70 and HSP70 mRNA was higher in the jejunum (p<0.01) and the ileum (p<0.05) of the HS. In the HS duodenum the levels of HSP90 were lower and then higher (p<0.01), and the HSP90 mRNA was higher (p<0.01). The expression of both HSP90 and HSP90 mRNA was higher in the HS jejunum (p<0.05). The levels of HSP90 were lower while the HSP90 mRNA was higher in the HS ileum (p<0.01). These results indicate that heat stress disturbed the expression of HSP60, HSP70, and HSP90 in the small intestine of chicks.
Under routine feeding conditions, 1-day-old male chicks were randomly divided into control group (CK), heat-stress group (HS), and GABA + heat stress group (GABA+HS). The thymus contents of IL-1, IL-2, TGF-β1, IFN-γ, GH and HSP70 were determined by enzyme-linked immunosorbent assays. The results showed that: (1) IL-1 and TGF-β1 contents of HS group were significantly lower than those of the CK group (p<0.05), and those of the GABA+HS group were significantly higher relative to the HS group (p<0.05); (2) IL-2 and IFN-γ contents of the HS group were significantly higher than those of the CK group (p<0.05), and those of the GABA+HS group were significantly lower relative to the HS group (p<0.05);(3) the thymus GH content of all three groups first increased and then decreased. The expression levels GH of the HS and GABA+HS groups were significantly lower than CK group (p<0.05); and (4) HSP70 expression levels in the thymus were significantly higher in the HS and GABA+HS groups relative to the CK group (p<0.05). These results indicate that heat stress affected thymus development, immune functions, and overall growth of chickens. Furthermore, it was shown that feeding GABA may significantly improve the immune responses of heat-stressed chickens by increasing the expression levels of IL-1 and TGF-β1, and effectively alleviate the negative effects of heat stress on thymus development by changing HSP70 expression and GH secretion.
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