As high temperature and relative humidity (RH) are the main environmental factors causing heat stress, the temperature–humidity index (THI) serves as an indicator of heat stress in livestock animals. This study aimed to determine the effects of heat stress on the laying performance, physiological responses, egg quality, and blood profile of laying hens by subjecting them to environmental conditions with varying THI levels (68–85) for 28 days. The indicators of laying performance, such as feed intake (−30%) and egg production rate (−11%), significantly decreased in the hens exposed to severe heat stress (33 °C, 66% RH) compared to those exposed to thermoneutral conditions (21 °C, 68% RH). Moreover, severe heat stress reduced the egg yolk color, eggshell thickness and strength, and Haugh units of the eggs produced by the laying hens. Furthermore, a significant increase in serum K⁺ and a decrease in Na⁺ levels were observed in the hens subjected to severe heat stress compared with those under thermoneutral conditions. Our results indicate that heat stress alters the physiological responses and metabolism of laying hens, resulting in a lower egg quality and production rate.

This study investigated the effect of dietary astaxanthin (AST) on the meat quality, antioxidant status, and immune response of chickens exposed to heat stress. Four hundred and eighty male broilers were assigned to four treatments including AST0, AST20, AST40, and AST80 with 0, 20, 40, and 80 ppm astaxanthin supplementation levels, respectively. There was a linear decrease of malondialdehyde (MDA) in leg muscle. Catalase and superoxide dismutase levels in the plasma were linearly increased. There was a linear increase in the level of total antioxidant capacity in the leg muscle. The 3-ethylbenzothiazoline-6-sulfonate reducing activity of leg muscle was significantly increased in the AST80 treatment. The AST40 treatment showed an increase in 2,2-diphenyl-1-picrylhydrazyl radical scavenging capacity of leg muscles. Breast meat redness and yellowness were linearly increased. The astaxanthin-supplemented treatments exhibited lower drip loss and MDA concentration of leg muscle compared with the AST0 treatment at days 3 and 9 of storage. Supplementation of 40 or 80 mg/kg astaxanthin significantly decreased heat shock protein (HSP)27, HSP70, tumor necrosis factor alpha, and interleukin-6 expression in the livers. The feather corticosterone was significantly lower in the astaxanthin-supplemented treatments than in the AST0 treatment. In conclusion, astaxanthin decreased the hyperthermic stress level and improved meat quality, and antioxidant status of chickens exposed to heat stress.

Environmental factors such as stocking density and high temperature can cause oxidative stress and negatively affect the physiological status and meat quality of broiler chickens. Here, we evaluated the effects of heat stress on the growth performance, antioxidant levels, and meat quality of broilers under different stocking densities. A total of 885 28-day-old male broilers (Ross 308) were subjected to five treatments (16, 18, 21, 23, and 26 birds/m²) and exposed to high temperatures (33 °C for 24 h) for 7 days. High stocking density (23 and 26 birds/m²) resulted in significantly decreased body weight (p < 0.01) and superoxide dismutase activity in the blood (p < 0.05) and increased (p < 0.05) rectal temperature and corticosterone. Additionally, the concentrations of heat shock protein 70 and malondialdehyde in the liver were higher in the 26 birds/m² group (p < 0.05). Similarly, the 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity of breast meat increased linearly as the stocking density increased (p < 0.05). There was increased shear force in breast meat at low stocking density (p < 0.01). Thus, lower stocking density can relieve oxidative stress induced by high temperatures in broilers and improve the antioxidant capacity and quality of breast meat during hot seasons.

This study was performed to investigate the effects of apparent metabolizable energy (AME_n) and protein levels on laying performance, egg quality, blood parameters, blood biochemistry, and apparent total tract digestibility of energy and nutrients in diets fed to laying hens in an aviary system. A total of 560 Hy-Line Brown laying hens (age = 30 week) were distributed in a completely randomized experimental design in 2 × 2 factorial arrangements with 2 metabolizable energy levels (2700 and 2800 kcal AME_n/kg) and 2 protein levels (16.5 and 14.5% CP). Four treatments and four replicates of 40 birds each (stocking density = 15 birds/m²) were prepared. Results revealed no significant interaction between AME_n and CP in the diet in terms of egg production, floor eggs, broken and dirty egg production, egg mass, feed intake, and feed conversion ratio of laying hens. However, egg weight was affected. As dietary energy and CP levels (2800 kcal of AME_n/kg and 16.5% CP) increased, egg weight increased (p < 0.05). Egg weight, feed intake, and feed conversion ratio significantly differed (p < 0.05) as the energy content in the feed increased. Ether extract significantly varied (p < 0.05) as the energy content in the feed increased. In conclusion, laying performance and egg quality of Hy-Line Brown laying hens in the middle stage of egg production (30 to 50 weeks) were not affected by different dietary energy and protein levels, but feed intake decreased with an increasing level of AME_n in diets. Ether extract significantly varied as the energy content in the feed increased.

We studied the effects of photoperiods on the growth performance, blood profile, welfare parameters, and carcass characteristics of broilers. A total of 336 male broiler chicks (Ross 308) were randomly allocated into 4 treatments (84 birds per treatment with 4 replicates), based on the following lighting regimen: 24 h continuous light (24L), 18 h continuous light (18L:6D), 8 h continuous light (8L:16D), and intermittent light (4L:2D). Body weight and feed intake of 7- and 35-day-old broilers were measured. At 5 weeks of age, 12 birds per treatment were selected for blood collection and carcass analysis. Body weight, body weight gain, and feed intake were the lowest in the 8L:16D treatment (p < 0.05). The heterophil-to-lymphocyte ratio, aspartate aminotransferase, interleukin-6, and corticosterone levels in the 24L treatment increased significantly when compared to that in the 18L:6D treatment (p < 0.05). The footpad dermatitis score was significantly lower in the 18L:6D and 8L:16D treatments than in the 24L and 4L:2D treatments (p < 0.001). There was no significant difference in the carcass and meat characteristics, except for the shear force of breast meat (Pectoralis major), which was the lowest in the 8L:16D treatment (p < 0.05). These results indicate that a photoperiod of 18 h resulted in an improvement in the performance and welfare of birds and a simultaneous decrease in stress level. However, further research is needed to establish a lighting regimen that satisfies both the productivity and welfare requirements of broilers in different feeding phases.