RESUMO
The present work was carried out to investigate the effects of dietary propolis supplementation to laying Japanese quail (Coturnix coturnix japonica) on egg production, egg quality, physiological and immunological aspects under heat stress conditions. A total of 200, 21-day-old, Japanese quail females were distributed equally into standard wired cages in two identical environmentally-controlled rooms (10 cages per room, 10 birds per cage). From 29-70 d of age, the quail birds in the first room remained at a normal temperature of 24°C (C group), whereas the quail birds in the second room were kept under heat stress at 35°C (HS group). Each group was further assigned to 2 propolis subgroups (5 cages per subgroup); one of them received a basal diet without propolis supplementation (-PR subgroup), while, the other received 1 g propolis/ kg basal diet (+PR subgroup). In the present study, performance and egg production of laying quail were significantly (P<0.001) impaired by HS treatment and improved by the PR treatment. Similarly, the negative and positive effects of HS and PR, respectively, were appeared on the egg shell thickness and yolk index. Stress indicators in laying quail were significantly (P<0.001) increased by HS, while, PR significantly (P<0.05) moderated these levels in the HS+PR group when compared to the HS-PR quail group. In addition to the positive impact of PR on the plasma levels of calcium, phosphorus, and albumin, it also normalized the plasma levels of alanine aminotransferase and cholesterol in the heat-stressed quail birds. Moreover, the quail birds in the HS groups expressed lower immunological aspects than those in the C group, while, the addition of propolis to the diets enhanced the immune status of laying quail birds under HS conditions. These results strongly suggest that dietary propolis supplementation could be a successful attempt to maintain the performance and egg production of laying Japanese quail at convenient levels under heat stress conditions.