Effect of thermal manipulation during incubation and heat challenge during the early juvenile stage on production parameters of broilers reared under a tropical climate

Heat stress induces economics losses in poultry production. Several studies have shown that this negative effect can be reduced by heat treatments like thermal manipulation during incubation (TMI) and early age thermal conditioning (ETC). The aim of this study was to investigate the effects of TMI on embryo development and the effects of TMI and ETC on productive performances of broilers under a tropical climate. The study involved 1000 Ross 308 broiler hatching eggs incubated at standard incubation conditions (37.8 degrees C at 60% relative humidity = RH) until embryonic day (E) 7. Then the eggs were divided into two groups: a control group (Ci) incubated at standard conditions until hatch and a treatment group (Ti) subjected to TMI (39.5 degrees C at 65% RH) for 12 h/d from E7 to 16. Chicks were assigned to one of two treatments at 3 days of age: chicks from the Ci group were assigned to CiP0 (chicks from eggs incubated normally and reared without ETC) and CiP1 (chicks from eggs incubated normally but exposed to ETC). Chicks from the Ti group were allocated to TiP0 (chicks from incubation with TMI and reared without ETC) and TiP1 (chicks from incubation with TMI and exposed to ETC). Microclimatic data (temperature 22 -34 degrees C and 58-70% RH) were recorded. Results indicated higher (p<0.001, p = 0.002) hatchability and chick quality in the Ci group. Final body weight was influenced by TMI and ETC. Feed conversion and feed intake were reduced by TMI, but not by ETC, which had an effect on mortality rate. A significant effect of TMI x ETC was observed on daily weight gain and mortality rate. In conclusion, ETC had a good and lasting impact on growth and survival and TMI improved FCR of broilers under a chronic hot environment. ETC plus TMI adversely impacted growth but improved survivability of broiler chickens.