In ovo betaine and heat acclimation affect hatching results, growth performance and immunity of the broilers under cyclic heat stress.

This study investigated the effects of in ovo betaine and thermal manipulation during incubation on growth performance, and some immune parameters of broilers under cyclic heat stress (CHS). Eggs were divided into 5 groups and incubated at 1) 37.8 °C and 60% relative humidity (Control incubation and not-injected, CI); 2) eggs were incubated at CI and in ovo betaine injected into yolk sac on d 11 (E11) (CI + In ovo); 3) eggs were exposed to 38.8 °C for 8 h between 10 and 18d of incubation (heat acclimation, HA); 4) eggs were incubated at HA and in ovo betaine applied (HA + In ovo); 5) positive control: eggs were incubated at CI and injected with saline. Hatched chicks were raised under standard management conditions until 21 d, between 21 and 42 d half of the chickens in each incubation treatment were kept either at optimum (OPT) or at CHS. In ovo and HA did not affect hatching performance. In ovo increased thymus and spleen weights of chicks. Serum IgG was higher in HA + In ovo chicks. From d 7 to 21, in ovo chicks were heavier body weights, consumed more feed, and better feed conversion than those from CI. The body weights of HA chickens were similar in OPT and CHS on d 28 and 35. CHS reduced the body weight of CI chickens which was compatible with their feed consumption. Moreover, feed intake of HA + In ovo chickens exposed to CHS was higher than those not injected indicating that HA + In ovo enhanced thermoregulation of chickens under CHS.