Early-age cold conditioning of broilers: effects of timing and temperature

1. The aim of the present study was to determine the effects of early-age cold conditioning (CC) on performance, ascites mortality, thyroid hormones status and immune response (leucocytes count) of broiler chickens. 2. A total of 336 chicks at 2 and 3 d of age were exposed to 20 or 25 degrees C (for 3 or 6 h) in a 2 x 2 x 2 factorial experiment, while a control group was kept under normal temperature conditions (30 degrees C). Thereafter, both control and cold conditioned birds were reared under standard conditions until 42 d of age. 3. The results showed that performance (weight gain and feed efficiency) was improved by CC at the end of the rearing period. Carcase traits (breast, thigh and abdominal fat percentage) were not affected by different treatments. Heart weight was lower in cold conditioned birds accompanied with lower ascites mortality. Total leucocyte count was higher in CC birds. Higher concentrations of thyroxin (T-4) were found in plasma of treated groups, while triiodothyronine (T-3) to T-4 ratio was decreased. 4. In conclusion, it seems that early age CC improves performance and reduces ascites mortality of broilers through altered thyroid hormones metabolism and leucocyte function. According to the results, the best timing for CC of broilers was 20 degrees C for 6 h at the age of 2 d, and no significant benefit was observed by repeated CC.