Heat stress impairs the nutritional metabolism and reduces the productivity of egg-laying ducks

This research was conducted to determine the effect of heat stress on the nutritional metabolism and productivity of egg-laying shelducks. Healthy shelducks (n = 120) in the early laying stage (uniform body weights and normal feed intakes) were randomly assigned to two identical climate chambers and exposed to constant high temperature (34 °C) or control temperature (23 °C) for 28 d. The heat-exposed ducks had reduced feed intakes and laying rates (P < 0.05), increased frequency of panting and spreading wings and dull featheration; egg weight, eggshell thickness and strength, and Haugh unit also decreased and malondialdehyde (MDA) content of egg yolk increased (P < 0.05). Compared with the control ducks, the plasma concentrations of HCO3−, phosphorus, glucose, thyroxine and activities of glutamic-pyruvic transaminase and glutamic oxaloacetic transaminase were decreased, while there were increased concentrations of corticosterone (P < 0.05). The content of MDA and lactate in plasma and liver was greater in heat-exposed than in control ducks, but superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), total antioxidant enzymes (T-AOC) activities and glutathione (GSH) contents were less. The expression of HSP70 gene expression in the liver was increased in heat-stressed ducks. The relative weight of oviduct, number of large ovarian follicles, length of the oviduct all decreased (P < 0.05) in heat-treated ducks, as did expression of carbonic anhydrase and calcium binding protein genes in the shell gland as a result of heat stress. In summary, heat stress decreased the productivity of ducks, which related to reduced feed intake, protein synthesis, endocrine dysfunction, less antioxidant capacity, and derangement of calcium and phosphorous balance.