Resumo:
The effects of the pre-natal thermal manipulation technique, with eggshell temperature control, were evaluated on incubation performance (egg weight loss, fertility, hatchability, mortality, and culling), chick quality (weight, length, yolk-free body weight, residual yolk weight, relative organ weights and navel score), incubation duration, embryonic morphology, shell parameters (weight, thickness, Ca, P, Mn, and Mg), yolk composition (Ca, P, Mn, and Mg), cloacal temperature, blood parameters (Ca, P, GH, T3, T4, PTH, calcitonin, vitamin D3, alkaline phosphatase, glucose, uric acid, lactate, liver glycogen, and blood gas analysis), and bone analysis (Ca, P, Mn, Mg, morphometry, biophysics, and mechanics) in one-day-old chicks. A total of 2,408 eggs from 52-week- old Cobb 500® heavy breeders were distributed into four single-stage incubators, each with a capacity of 602 eggs. The incubators were set to maintain the eggshell temperature (EST) at 37.8°C during the incubation period. Between the 8th and 18.5th days of incubation, for 6 hours per day, one incubator was adjusted to an EST of 36.7°C (MT-L), another to 38.9°C (MT-H), and a third to 39.4°C (MT-VH). The control incubator remained under the initial settings. Thermal manipulation at an EST of 36.7°C worsened most incubation performance variables, prolonged the incubation time, increased cloacal temperature, worsened chick quality parameters, relative organ weights (heart, liver, intestines, lungs, spleen, pancreas, and bursa), impaired the demineralization of the eggshell and yolk, disrupted calciotropic hormones, and consequently hindered bone development in embryos and one-day-old chicks. Therefore, this treatment is not recommended. Conversely, thermal manipulation with eggshell temperature control at 38.9°C or 39.4°C resulted in lower cloacal temperature, greater mobilization and utilization of minerals from the egg components, and consequently better bone development, without impairing incubation performance or chick quality. This technique proved to be a viable and beneficial tool, and further evaluation of the long-term positive effects during bird rearing is recommended.
