Improvement of cold resistance and performance of broilers by acute cold exposure during late embryogenesis

The aim of this study was to fine-tune previous acute cold exposure treatments of broiler embryos during late embryogenesis to improve lifelong cold resistance and performance. Six hundred Cobb hatching eggs were incubated under standard conditions and then exposed to 3 treatments: control; cold treatment in which embryos were exposed to 15 degrees C for 30 min on d 18 and 19 of incubation (30x2); and cold treatment similar to 30x2 but with 60-min exposures (60x2). Egg shell temperature (T(egg)) and heart rate (HR.) were monitored pre- and posttreatment. Upon hatching, hatchability, body weight; and body temperature were recorded. From 14 to 35 d of age, three quarters of the chickens in each treatment were raised under ascites-inducing conditions (AIC) and the remaining birds were raised under standard brooding conditions (SBC). The T(egg) and HR decreased significantly in response to increased exposure time on d 18 of incubation. On d 19 of incubation, before the second cold exposure, the 30x2 group showed greater T(egg) and HR than the controls, and during the second exposure they maintained these parameters better than the 60x2 embryos. No treatment effect on hatchability was observed. At 35 d of age ascites incidence among 30x2 chickens under AIC was significantly less than that among the controls (P < 0.01), and body weight of these chickens under either SBC or AIC was significantly higher than that of the controls. Under SBC relative breast muscle weight was significantly higher in 60x2 chickens, whereas the relative heart weight was higher in both cold-treated groups than in the controls. It can be concluded that repeated short acute cold exposures during late embryogenesis significantly reduced ascites incidence and improved growth rate under either SBC or AIC. These results may be related to a prenatal epigenetic adaptation of the thermoregulatory and cardiovascular systems to low ambient temperature.