China stands as the world’s foremost market for duck production and consumption, with approximately 5.59 billion ducks produced in the country in 2022. Among these, Pekin ducks constitute 80%, while other breeds make up the remaining 20%. Notably, the predominant strains within the Pekin duck category employed for meat production include “Grassland duck,” “Zhongxin duck,” and “Z-type Pekin duck” (1–4). The methods of waterfowl farming are continually evolving, and indoor dryland farming has been extensively utilized in the duck industry. The change of environmental temperature and humidity, together with a variety of physiological situations including age, fasting and food intake, stress circumstances and inflammation status induce changes in internal temperature which are followed by changes in body surface temperature (5, 6). The pivotal role of ambient temperature in the indoor environment of dryland duck farming has been widely acknowledged (7–10). In addition, as the global trend of climate warming becomes increasingly apparent, research on the impact of temperature on the breeding industry is pressing. The economic efficiency of the poultry industry is closely linked to the growth rate and mortality rate in poultry production systems, and ambient temperature plays a decisive role in the health and growth of animals (11–15).

Poultry are susceptible to temperature due to factors such as rapid metabolic rate, increased basal metabolic heat production, and rapid growth and production. Heat dissipation is an important challenge for poultry because they lack sweat glands. In addition, feathers and fluff have a good insulation effect, which makes the heat dissipation of poultry more difficult. To balance the increased metabolic heat production, the body secretes more leptin to stimulate the hypothalamus to reduce the animal’s appetite, thereby reducing food intake (12, 16, 17). Animals will increase feed intake and accelerate the body’s heat production rate to combat hypothermia in cold environments, prolonged hypothermia affects animal performance and causes disease and thus increased mortality (11, 18, 19). Current research on environmental temperature in meat poultry farming mainly focused on broilers and geese, with fewer reports on ducks. Chronic heat stress induced by elevated environmental temperatures can diminish broiler chickens’ growth performance, pectoral muscle yield and meat quality (20–23), as well as lead to physiological changes in intestinal morphology and oxidative damage (24, 25). When the temperature exceeds 25.19°C, the growth performance and fat deposition of geese are inhibited, and the morphology of the duodenum is more susceptible to damage (26). Sun et al. estimated the upper critical temperature for the optimal growth of Pekin ducks through a model. The BW, pectoral muscle weight, thigh muscle weight, pectoral muscle ratio, abdominal fat and abdominal fat ratio of Pekin ducks all show a linear or quadratic decrease with increasing temperature (27). High ambient temperatures also increase serum protein cortisol levels in breeding ducks and reduce growth and reproductive performance (14).

In our previous research, we found that the environment with 74% relative humidity is more favorable for Pekin ducks (3). However, most of the current research on the impact of temperature on Pekin ducks is based on a 60% humidity environment (28). Moreover, many reports indicate that temperatures above 30°C have significant adverse effects on poultry (29). Therefore, this study will investigate the effects of 20–29°C on Pekin ducks on the basis of 74% humidity. We will further explore the optimal environmental temperature range for the growth of Pekin ducks, providing empirical support and theoretical basis for the environmental parameter regulation in the waterfowl dry farming model.

In our research, the mortality rate was remarkably low. Throughout the entire rearing period, each group had only 2–3 ducks that died (Supplementary Table S1). It’s a common phenomenon in the production of meat ducks and does not impact the experimental results.

Commercial poultry breeds are fast-growing animals that rely on evaporative heat loss to regulate their body temperature, and temperature changes affect feed intake, growth and thermoregulation (26, 37, 38). Increased temperature leads to a decline in the production performance of Pekin ducks. From the results of this experiment, there is a negative correlation between temperature and the market weight of Pekin ducks (Supplementary Table S2). This finding was supported by previous research on chickens (21, 38, 39), ducks (28, 40) and geese (26). And the results of ADFI also followed the pattern of BW changes. However, there was no significant difference in F/G, which was one of the reasons consistent with the trends of ADFI and ADG. This suggested that within the range of 20–29°C, there was no variation in feed efficiency for Pekin ducks. This implied that the body weight of Pekin ducks is almost entirely determined by feed intake. Changes in ambient temperature alter the thermoregulation of Pekin ducks, requiring them to regulate the generation of metabolic heat by adjusting feed intake. The range of 20–29°C did not impact the digestive capacity of Pekin ducks, but this result may be challenged when the temperature exceeds 29°C (26, 28).

Additionally, we observed an increased trend in BW reduction when the temperature exceeded 23°C. This indicated that the suitable temperature range for the growth of Pekin ducks was not a fixed value but rather a temperature interval. When the temperature exceeded the upper critical limit, the BW decreased rapidly. Many studies had also confirmed the existence of an upper critical temperature in duck farming and estimated it using models, including other poultry (26, 28, 40). Homeothermic animals can regulate body temperature within a certain range, and damage occurs once it exceeds the body’s regulatory capacity. This is the reason for the existence of critical temperature. Sun et al.’s study suggested that the upper critical temperature for Pekin ducks was 27.4°C, while Xie et al.’s result was 31.3°C (28, 40). The possible reason for this difference was the different ages of ducks in the two studies, indicating that the ability of ducks to regulate body temperature changed with age, and there were different critical temperatures at different growth stages. In this study, the age of the ducks was consistent with Sun et al., and we found that the upper limit critical temperature was less than 27.4°C after we fed the results into his model. The potential cause of this outcome may be attributed to variations in humidity. In the study conducted by Sun et al., the environmental humidity was set at 60%, while in our research, the humidity was maintained at 74%. This difference could be a significant factor contributing to the leftward shift of the upper critical temperature coordinates in the model.

Genetic factors, age, sex, nutritional level, growth environment and other factors affect body size traits and slaughter traits (23). Body size traits are phenotypic characteristics that respond to the growth and development of the animal, and the measurement of body size traits may be used to select favorable traits and examine the high-quality genetic factors of a breed. The body conformation and slaughter traits of animals are highly correlated with production performance. In this study, the body oblique length, keel length, and chest depth of ducks decreased with increasing temperature, and these indicators showed a consistent trend with changes in BW and ADFI. The potential cause of this outcome may be attributed to temperature influencing the feed intake of ducks, thereby influencing the body development of ducks. Organ indices are important indicators reflecting organ growth and development, directly affecting the nutritional absorption efficiency, metabolism, and growth rate of the organism. Many studies have shown that the environment and feeding levels have a significant impact on organ development (41). The spleen is an important immune organ in ducks, and the liver is an organ for lipid metabolism in the body. Their indices represent the strength of the corresponding functions. In this study, although there were significant differences in liver weight and spleen weight, there were no significant differences in the corresponding ratios. In view of this, the temperature range of this experiment may not have a direct impact on the metabolism and immune function of duck bodies. In this study, there were significant changes in pectoral muscle weight and thigh muscle weight, but there were no significant differences in the corresponding relative weigh. The probable cause for this phenomenon is that the temperature range in this experiment did not impact the meat production efficiency of ducks. However, Zhang et al. (20) found that chronic high temperature reduced the proportion of breast muscles in chickens and increased the proportion of thigh muscles, which was inconsistent with the results of this study. Nevertheless, there was no mention of the relative humidity during the experiment in his paper, making it difficult for us to ascertained if this variation is attributable to relative humidity.

Meat quality is influenced not only by genetic factors but also by environmental factors such as temperature, humidity, light, and harmful gas content. The indicators for evaluating meat quality include pH, meat color (a*, b*, and L* values), shear force, dripping loss, cooking loss, fat, ash and protein (17, 23, 42, 43). Currently, research results on the cooking loss of Pekin ducks under different temperatures are inconsistent. In this study, cooking loss was significantly reduced with the increase of temperature, and the study by Zhang et al. supported the results of this research (20). In this environment, the amount of water and other nutrients lost in the muscle decreased to maintain higher water-holding capacity. However, there was no significant difference in cooking losses in Sun’s study (27). The reasons for this difference may be the different temperature ranges between this study and that of Sun et al., and there may be interactive effects between different relative humidity and temperature, but this has not been clearly reported. There was evidence that cooking loss was negatively correlated with shear force, but the results of this study have not confirmed it (44).

Changes in muscle pH reflect the rate and intensity of glycolysis in muscle, and elevated muscle acidity values affect muscle protein denaturation, meat color differences and tenderness (45). Meat color is used as a visual sensory measure of meat quality and freshness. The results of current studies on meat color and pH are mixed. One study reported reduced L*, b* and pH of pectoral muscle after heat stress treatment for 24 h (46). Compared with normal temperature, high temperature feeding significantly increased the L* and b* of breast meat, and significantly reduced a*, white meat and water seepage (20). In this study, there was no significant difference in pH value, which is consistent with the results of Sun et al. However, research suggested that increased physiological stress and physical activity of animals during transportation or prior to slaughter leadeed to depletion of muscle glycogen and an increase in pH, which result in dark, firm and dry meat (DFD) (47). There was a significant difference in b* values in this study, but the numerical values deviated significantly from the results of other studies, and the data dispersion was high, possibly due to measurement errors. Therefore, the results may not accurately reflect the real situation. The nutritional value of muscles is primarily evaluated by the content of water, protein, fat and ash. Protein determines the nutritional value of meat, and fat is the main carrier of meat flavor. Adequate fat in muscles is of great significance to the palatability and flavor of meat. In this study, there was no significant difference in protein, fat, and ash content. These results indicated that the temperature range in this study did not affect the nutritional value of muscles.

The antioxidant system is the body’s defense system against free radical damage, which is closely related to cell differentiation and tissue development in vivo. Maintaining redox balance is essential for effective immunity and health. Therefore, the determination of antioxidant indices may reflect the pattern of free radical metabolic changes in vivo (15, 23, 48–50). There are differences in the sensitivity of various antioxidant indicators in the serum of experimental ducks to temperature treatments. In this study, the T-AOC content in the serum of T29 significantly increased. And it was found that SOD activity significantly increased when the temperature exceeded 26°C. This result may be attributed to the increased demand for the body’s antioxidant defense against oxidative damage due to the rise in temperature, a notion supported by the study of Niu et al. (51). Reports indicated that acute heat stress treatment significantly increased SOD levels, and with increasing treatment intensity (52), SOD activity showed a gradient increase (53). This suggests that, under the premise of 74% relative humidity, the temperature range of 20–26°C may be conducive to reducing oxidative damage in Pekin ducks.

In this experiment, the method used to adjust environmental parameters in the artificial environmental control room involves blowing in freshly heated or cooled air. Sensors are positioned around the room, and every 5 seconds, they report to the control center. The new air is introduced only when the average temperature of all sensors reaches the target temperature, without any preprocessing. This may result in temperature deviations from the set value at different locations within the room and a lag in control. Consequently, influenced by various factors, the temperature fluctuates around the set value, creating a dynamic equilibrium. The impact of this on the experimental results is minimal and unavoidable. In addition, we have some challenges in determining the quality of meat. For example, the time it takes for each sample to be removed from the carcass until measured cannot be guaranteed to be exactly the same, which may have some impact on meat color. The insertion position and Angle of the pH meter may also produce errors in the test results. It is worth considering how these potential influencing factors can be further reduced in future studies. Despite this, the results obtained in this experiment remain highly meaningful.

In conditions with a relative humidity of 74%, temperature significantly affects the growth performance, slaughtering traits, muscle quality and antioxidant function of Pekin ducks. When the ambient temperature exceeded 26°C, the body weight and feed intake of Pekin ducks significantly decreased, and the development of body size and muscle weight followed this pattern. At ambient temperatures of 20°C and 23°C, the growth development and serum redox status of Pekin ducks were more ideal and stable. In specific relative humidity conditions, the temperature conducive to the growth of Pekin ducks may be a range rather than a fixed value. This study can offer data support for livestock production until more in-depth research is demonstrated. In summary, at 74% relative humidity, the suitable growing temperature for Pekin duck is 20–23°C.

The original contributions presented in the study are included in the article/Supplementary material, further inquiries can be directed to the corresponding author.

The animal study was approved by Animal Ethics Committee of Jiangsu Academy of Agricultural Sciences. The study was conducted in accordance with the local legislation and institutional requirements.

CX: Conceptualization, Data curation, Methodology, Validation, Writing – original draft, Writing – review & editing. DS: Investigation, Methodology, Writing – original draft, Writing – review & editing. YL: Investigation, Methodology, Writing – original draft, Writing – review & editing. ZP: Data curation, Formal analysis, Writing – original draft, Writing – review & editing. ZD: Data curation, Formal analysis, Writing – original draft, Writing – review & editing. FC: Data curation, Formal analysis, Writing – original draft, Writing – review & editing. RG: Validation, Writing – original draft, Writing – review & editing. RC: Validation, Writing – original draft, Writing – review & editing. ZS: Supervision, Writing – original draft, Writing – review & editing. SY: Conceptualization, Funding acquisition, Project administration, Writing – original draft, Writing – review & editing.