injection of ascorbic acid and higher incubation temperature modulate blood parameters in response to heat exposure in broilers.

1. This study analysed whether injection of ascorbic acid before incubation and at high incubation temperature influenced blood characteristics and performance in broilers reared in different temperature conditions. 2. A total of 3,000 fertile eggs from broiler breeders (Cobb®) were randomly divided into three incubation treatments: no ascorbic acid injection and egg incubation at 37.5°C (control); no ascorbic acid injection and egg incubation at 39°C; ascorbic acid injection prior to incubation (6 µg AA/100 µl water) and egg incubation at 39°C. 3. Male chicks hatched from the three incubation treatments were submitted to three distinct rearing temperatures (control, cold and hot) from the third week of age onwards (540 chicks were divided into 6 treatments with 5 replicates per treatment). 4. Measurements at 42 d showed that, after egg incubation at 39°C, the haematocrit, haemoglobin values, ionised calcium and glucose concentrations were increased and base excess values were reduced. However, injection of ascorbic acid normalised all these parameters. 5. Partial CO and O pressure were higher with increased rearing temperature. Blood pH was lower when eggs were incubated at 39°C and injected with ascorbic acid. injection of ascorbic acid induced leucocytosis due to lymphocytosis and heterophilia, restored basophils rate and led to monocytopoenia. Leucocytosis was triggered by hot rearing temperature due to lymphocytosis, eosinophilia and heterophilia. 6. The results obtained in this study showed that injection of ascorbic acid before incubation may serve as a long-term stimulator and modulator of the broiler immune system, and that high incubation temperatures induce adaptations in the electrolytic balance, minimising or avoiding the occurrence of respiratory alkalosis under hot rearing temperature.