Mild heat stress changes the microbiota diversity in the respiratory tract and the caecum of layer-type pullets

Abstract The present study aimed to research the effects of cyclic heat environment on the microbial diversity and structure of respiratory tract and cecum of chicken. A total of 360 layer-type pullets at 11-weeks of age were subjected to different temperature treatments for 10 weeks: constant 22 °C; cyclic temperature 22-24 °C, 22-26 °C, 22-28 °C, 22-30 °C, the ambient temperature increased from 10:00, reached the set point within 1 h and maintained until 18:00, thereafter the temperature was restored to 22 °C, and the relative humidity was maintained at 60%. The result showed that feed intake of the chickens on ambient temperature 30 °C group was significantly lower than that of the chickens on ambient temperature 24 °C. The white blood cell (WBC), red blood cell (RBC), lymphocyte, hemoglobin (Hb) and pecked-cell volume (PCV) content were highest at 24 °C on 14, 16, 18 weeks. The ratio of CD3+CD4+ / CD3+CD8+ T cells was lowest at 30 °C. Meanwhile, the abundance of cecum bacteria in chickens at 30 °C was lower than that was at 24 °C. Cyclic heat environment temperature treatment did not significantly affect the concentration of SIgA in chicken bronchoalveolar lavage fluid (BALF) levels during 10 weeks of trial. The diversity index analysis showed that effect of 24 °C on the cecum flora of chickens was optimal. Abundance of Firmicutes bacteria in the lung flora and cecum flora was lower at 30 °C compared to 24 °C group. Similarly, the microorganism, Brevibacillus in the BALF was also significantly lower at 24 °C. In conclusion, cyclic 24 °C treatment was beneficial for the feed intake, blood routine indexes, microflora structure of the cecum and respiratory tract in laying pullets.