Effects of thermal manipulation during late incubation period on post-hatch thermotolerance in ostrich

The effects of thermal manipulation (TM) during late ostrich embryonic development on hatchability, body weight, biochemical and hormonal changes, and the ability of hatching chicks to cope with thermal challenge in days 6-8 of age were examined. At 35 days of incubation, two hundred fertile eggs were weighed and divided into two equal groups with five replicates. The first group was exposed to 36.5°C and 25% relative humidity (RH) (control), while the second group was exposed to 38.5°C and 45% RH for 3 h daily in days 35-37 of incubation (thermal manipulation). At days 6-8 of age, the hatched chicks from each treatment were randomly divided into two groups: control group (exposed to 32 ± 1°C), and thermal challenge group (exposed to 40 ± 1°C for 3 h daily). Hatchability rate was significantly lower with high incubation temperature as compared to the normal incubation temperatures. Embryonic TM and thermal challenge in days 6-8 of age reduced significantly total protein, albumin, and triiodothyronin concentrations and elevated uric acid, creatinine, triglycerides, and glucose concentrations as compared with the control. The level of corticosterone was significantly higher in the thermal challenge group as compared to the control. In conclusion, exposing the ostrich embryos to TM (38.5°C) during late embryonic development induced physiological changes that may represent epigenetic adaptation to TM. The same mechanisms are employed for increasing the ability to improve thermotolerance post-hatch.