Abstract
ABSTRACT This study aimed to evaluate the effect of thermal stress on the physiological and metabolic parameters in laying hens and the microbiological quality of eggs. The experiment was performed with 50 Rhode Island Red hens in the initial laying phase, under standard diet, lodged in 20 m² stalls under controlled temperature, for 30 days. The laying hens were randomly divided into two groups: G1 - the control group, which contained 10 hens exposed to the temperature of 17 ºC; G2 - the treatment group, which contained 40 hens exposed to the temperature of 30 ºC. The physiological parameters evaluated were: cloacal temperature, body surface temperature, heart rate, respiratory rate, and weight. Biochemical tests included total protein, albumin, globulin, and glucose. The group subjected to thermal stress showed lower body weight, increased heart rate, a slight increase in the respiratory rate, and increase in body surface temperature when compared with the control group (P < 0.05), although no significant differences were observed regarding cloacal temperature. As for the metabolic parameters, the treated group showed an increase in total proteins and globulins compared with the control group (P < 0.05), while albumin remained at basal levels. Additionally, hypoglycemia was observed in the treated group. Samples from egg shells and yolk were subjected to the analyses for the detection of Salmonella spp. These microorganisms were not detected amongst the egg samples.
Highlights
Animal welfare has been considered one of the top priorities of animal production, especially for laying hens, which require special care regarding environmental conditions
The group subjected to thermal stress showed lower body weight, increased heart rate, slightly increased respiratory rate, and increased body surface temperature when compared with the control group (P < 0.05), no significant differences were observed as for cloacal temperature (Table 1)
The body surface temperature was slightly higher in the treated group, with an increase of 3.1°C compared with the control group (Table 1)
Summary
Animal welfare has been considered one of the top priorities of animal production, especially for laying hens, which require special care regarding environmental conditions. The physiological and metabolic parameters of animals are altered under high environmental temperatures. Thermal stress causes direct losses in zootechnical performance, resulting in lower egg production and in lower egg quality (Attia et al, 2018; Liu et al, 2020). The significant development of the Brazilian poultry industry allowed a significant increase in egg production. The high performance of laying hens and egg quality are essential characteristics for producers (Castro et al, 2019). This study was to evaluate the effect of thermal stress on the physiological and biochemical parameters of Rhode Island Red laying hens and on the microbiological quality of their eggs
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