Effects of heat stress on laying performance, blood hormones and biochemical indices, egg quality, and intestinal digestive enzymes in laying ducks.

Chronic heat stress poses a major challenge to duck production by impairing reproductive performance and physiological homeostasis. This study investigated the effects of chronic heat stress on laying performance, reproductive physiology, blood biochemical indices, egg quality, intestinal digestive enzyme activities, and hepatic oxidative status in Gaoyou sheldrakes. Sixty 16-week-old ducks were randomly assigned to either a thermoneutral group (21 ± 2°C) or a heat stress group (35 ± 2°C, 24 h/day), with heat exposure initiated at 24 weeks of age. Compared with the thermoneutral group, chronic heat stress significantly reduced feed intake, laying rate, egg weight, ovarian development, serum estradiol and progesterone concentrations, and egg quality, while markedly altering blood biochemical parameters indicative of impaired nutrient metabolism and liver function. Heat stress also significantly decreased the activities of digestive enzymes in the small intestine and disrupted hepatic oxidative homeostasis, as evidenced by increased HSP70 and MDA levels together with reduced antioxidant enzyme activities. These findings demonstrate that chronic heat stress impairs laying performance through coordinated alterations in intestinal digestion, hepatic oxidative balance, nutrient metabolism, and reproductive endocrine function, providing new insights into the physiological mechanisms underlying heat stress-induced reproductive dysfunction in laying ducks and supporting the development of effective mitigation strategies for duck production under high-temperature conditions.