Mild heat stress changes the microbiota diversity in the respiratory tract and the cecum 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 wk of age were subjected to different temperature treatments for 10 wk: constant 22°C; cyclic temperature 22°C to 24°C, 22°C to 26°C, 22°C to 28°C, 22°C to 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, red blood cell, lymphocyte, hemoglobin, and pecked-cell volume content were highest at 24°C on 14, 16, and 18 wk. 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 at 24°C. Cyclic heat environment temperature treatment did not significantly affect the concentration of secretory immunoglobulin A in chicken bronchoalveolar lavage fluid ( BALF ) levels during 10 wk of trial. The diversity index analysis showed that the 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 than at 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.

Heat stress on microbiota composition, barrier integrity, and nutrient transport in gut, production performance, and its amelioration in farm animals

“…However, HS did not cause any changes in the gut microbiota communities at the phylum level on day 1, 3, and 28 [ 28 ]. The changes in abundances of bacteria at the phyla levels, particularly for Firmicutes and Bacteroidetes may not be considered to have its practical inferences for health benefits and diseases unless their compositional changes are studied at the lower taxa levels such as genus and species [ 33 ].…”

Bacillus subtilis-Based Probiotic Improves Skeletal Health and Immunity in Broiler Chickens Exposed to Heat Stress

“…The released bacteria and bacterial products such as lipopolysaccharide (LPS) cause neuroinflammation, activating the HPA axis to release CORT (or cortisol in humans) and the automatic nervous system (the sympathetic and parasympathetic systems) to release epinephrine (EP) and norepinephrine (NE), leading to biological disorders in the animals. Heat stress also damages the composition of the gut microbiota in animals [ 126 , 127 , 128 ], i.e., decreasing beneficial bacteria but increasing pathogenic bacteria [ 129 ], resulting in interrupted gut homeostasis and triggered the release of proinflammatory cytokines and oxidative agents [ 130 , 131 ].…”

Potential Use of Gut Microbiota Composition as a Biomarker of Heat Stress in Monogastric Species: A Review

“…Thus, the exposure length to high ambient temperatures is different for broilers and laying hens under the practical production environment. Studies investigating the effects of heat stress generally applied two- to four-week thermal treatment for broilers [ 17 , 45 , 53 ], and more prolonged treatment for laying hens [ 18 , 54 , 55 ].…”

“…In broilers, heat stress tends to increase the species richness and diversity of either cecal or ileal microbiota, with an exposure time ranging from two to four weeks [ 17 , 45 , 53 ]. While in laying hens, Wang et al reported a decreased species richness in hens after being exposed to heat stress for 10 weeks and the potential effects of mild cyclic heat stress on limiting the microbial growth in the cecum [ 54 ]. However, no difference in alpha diversity was noticed in the cecal microbiota of hens exposed to heat stress than the control group in another study with four-week exposure to heat stress [ 55 ].…”

“…Interestingly, when the heat-stress exposure length was prolonged to 7–10 weeks, opposite results of the Firmicutes-to-Bacteroidetes ratio were noticed in two laying hen studies [ 18 , 54 ]. Consistently, distinct clusters of gut microbes were detected between chickens in thermoneutral conditions and those under heat stress across studies [ 17 , 45 , 53 , 54 , 55 ]. This difference in beta diversity reflects the variation in microbial compositions between thermal treatment and control groups.…”