physiological, biochemical and metabolic responses of japanese quail (coturnix coturnix japonica) as affected by early heat stress and dietary treatment

the main objective of this study was to elucidate the effect of short- term exposure of japanese quail eggs to acute high incubation temperature on embryonic development and on the ability of post- hatched chicks to cope with subsequent heat stress conditions during the growing period. a total of 998 japanese quail eggs were divided into two groups, the first group (470 eggs) was maintained at the recommended incubation temperature (37.5 ˚c), while the second group (528 eggs) was exposed to 39.5 ˚c for two hours at days 3, 7 and 13 of embryogenesis. after hatching, chicks from each incubation temperature were randomly assigned to four dietary treatments, a control, a high-energy (+150 kcal me/kg diet more than the recommended level); a high-lysine (10% more than in the control diet) and a vitamin c supplemented diet. during the experimental period all of the quail were fed ad libitum and they received similar hygienic and managerial conditions. the rearing temperature was 32±2 ˚c during the entire experimental period. pre-hatching exposure of eggs to 39.5 ˚c did not significantly affect the post-hatching body weight and weight gain during the growing period. while, vitamin c or high-energy diet increased it. body temperature, respiration rate (rr) and the relative weights of the thymus, spleen and bursa of fabricius were not significantly affected by the pre-hatching temperature or the post-hatching dietary treatments. however, the high-energy and vitamin c diets caused obvious decreases in rr at 4 weeks of age. pre-hatching heat treatments caused a slight increase in the plasma triiodothyronine (t3) and plasma thyroxine (t4) concentrations, however, was significantly decreased by both the pre- hatching temperature and post- hatching dietary treatments at 6 weeks of age. based on the above results, it was concluded that pre-hatching exposure of quail eggs to high temperature and post-hatching feeding of a high-energy or vitamin c supplemented diet can be recommended for alleviating the deleterious effects of heat stress during the growing period.