EN
The effect of acetylsalicylic acid (ASA) injected in ovo on the 18th d of incubation on the hatchability, course of hatching, and thyroid hormone concentrations (thyroxine (T₄) and triiodothyronine (T₃)) in the blood of chicks exposed to control (CON) or hyperthermic (HT) conditions during hatching were investigated. Eggs (n=540) from a broiler breeder flock were incubated under standard conditions. On the 18th d of incubation they were injected with 0, 5, or 10 mg of ASA/egg and subsequently incubated at 37.2°C (CON) and 38.5°C (HT). The processes of external pipping and hatching were monitored from the 460th h of incubation, and the embryopathological analysis of the dead embryos was performed. Blood samples from 12 chicks from each group were collected immediately after hatching, and at the 12th, 24th, and 36th h following. The T₄ and T₃ concentrations in the plasma samples were measured radioimmunologically. There were no significant alterations in the embryonic mortality and chicken hatchability between the CON and HT incubation conditions. ASA treatment did not affect the hatching parameters under CON conditions; however, under HT conditions the lower dose of ASA reduced embryonic mortality and increased the hatchability. The hatching of the chicks was accelerated by about 8 h under HT conditions, too. A gradual decrease in T₄ and T₃ levels in CON and HT chicks was found, following the hatching. In embryos incubated under CON conditions, ASA treatment significantly increased the T₄ concentration at the moment of hatching. The opposite ASA effect was found at the 12th h after the hatching, as well as in chicks exposed to HT conditions (both at the moment of hatching and at the 12th h after it). Plasma T₃ concentrations in HT conditions were significantly lower at the moment of hatching and at 12th h after hatching. ASA treatment decreased the T₃ level at the time of hatching in chicks kept under CON conditions. The results obtained indicate that ASA injected in ovo at the 18th d of incubation does not affect the hatching parameters; however, it diminishes embryonic mortality and elevates their hatchability under hyperthermic conditions. The results of the thyroid hormone determinations suggest that treatment of the chicken embryo with ASA a few days before hatching reduces the unfavourable effects of heat stress conditions, which may appear in the hatcher.