Effects of in Ovo Exposure to Acetylsalicylic Acid and Hyperthermia on the Hatchability and Thyroid Hormone Concentrations in Newly-hatched Chicks

The effect of acetylsalicylic acid (ASA) injected in ovo on the 18 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 18 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 460 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 12, 24, and 36 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 12 h after the hatching, as well as in chicks exposed to HT conditions (both at the moment of hatching and at the 12 h after it). Plasma T3 concentrations in HT conditions were significantly lower at the moment of hatching and at 12 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 18 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.