New Zealand White rabbits tolerance to chronic thermal stress at different dietary energy/protein levels

•Increasing dietary energy and/or protein level were studied in heat-stressed rabbits.•Rabbit exposed to chronic heat stress had impaired growth and blood biochemistry.•High energy (HE) and/or high protein (HP) diet improved thermoregulatory indicators.•Heat-stressed rabbits fed HE and HP diet showed the highest economic efficiency.•Using HP and HE diet may be a useful tool to alleviate the hazards of heat stress. In hot environments, rabbits are exposed to heat stress, which leads to significantly reduced production performance, and consequently, economic losses. Hence, new nutritional strategies to alleviate the adverse effects of increasing temperatures have become highly needed. This study aimed to test the efficacy of the high-energy diet with or without high protein levels to improve the tolerance of growing rabbits raised under heat stress circumstances. A total of 75, 35-day-old male New Zealand White rabbits (598.1 ± 0.77 g) were used for 56 days. The rabbits were alienated into five treatment groups. The W-NP-NE group was kept during the winter season (thermo-neutral condition) and fed on the basal diet (normal protein and normal energy). The other four treatment groups were kept during the hot climate summer season. The S-NP-NE group was fed a basal diet. The S-NP-HE group was fed on a normal protein and high-energy diet, while the S-HP-NE group was fed a high protein and normal energy diet. The S-HP-HE group was fed a high protein and high-energy diet. The results revealed that chronically heat-stressed rabbits showed a reduction in feed intake, feed utilization, growth performance indices, red blood cells, white blood cells, blood hemoglobin, total protein, albumin, and glucose compared to the thermoneutral group. However, a significant increase in triglyceride, total cholesterol, aspartate aminotransferase, and alanine aminotransferase levels was obvious. A significant elevation in thermoregulatory indicators, including rectal temperature, respiration rate, and heart rate, was observed in S-NP-NE group. However, increasing dietary energy and protein levels alone or in combination significantly reduced the harmful impacts of chronic temperature stress on the rabbit's growth, feed utilization, thermoregulatory, and biochemical indicators. Rabbits of the S-HP-HE group showed the highest economic efficiency. In conclusion, increasing energy and protein concentration alone or in combination may be a practical tool to enhance the growth, thermoregu