Resumo:
The purpose of this study was to evaluate whether temperature variations (above or below that of the commercially recommended), applied constantly or intermittently, influence bone development and zootechnical performance of broilers. Two experiments were carried out using the following treatments: 1) TCO-C (Control eggshell temperature - 37.8°C throughout incubation); 2) TCO-B (36.7°C between days 8 and 18.5 of incubation); 3) TCO-A (38.9°C between days 8 and 18.5); and 4) TCO- MA (39.4°C between days 8 and 18.5). In experiment I, the treatments were applied constantly throughout the incubation period, while in experiment II, the temperatures were programmed to be manipulated for 6 hours a day in the selected incubation period. 800 male chicks from the incubation of eggs from the same batch of Cobb® breeder (with 45 weeks in experiment I and 52 weeks in experiment II), were housed in a conventional experimental shed, subjected to the recommended standard management conditions and created up to 42 days. The variables analyzed were: serum mineral (Ca and P), biochemical (alkaline phosphatase) and hormonal (GH, T3, T4, PTH and vitamin D3) profile; rectal temperature; mineral (Ca, P and ashes), morphometric (weight, length and width) and mechanical (breaking force for) characteristics of the tibia; bone and locomotion disorders (tibial dyschondroplasia, pododermatitis, valgo- varo deformity, latency-to-lie and gait score); zootechnical performance (weight, weight gain, feed consumption, food conversion and viability); and carcass yield and parts (chest, wing, thigh and thigh). In experiment I, all modified TCOs harmed (p≤0.05): the performance of the birds; the yield of carcass, chest, thigh and thigh; the serum contents of PTH and FA; the mineral bone levels and morphometric; and the VV score. High and very high TCO still compromised wing yield, rectal temperature, serum levels of Ca, P and vitamin D3, resistance and DT (p≤0.05). GH and PD and GS disorders have been shown to be negatively influenced only by very high TCO (p≤0.05). In experiment II, thermal manipulation (MT) at 36.7ºC harmed many variables (p≤0.05): general zootechnical performance; serum Ca, P, FA, PTH and vitamin D3; body temperature; and morphometry and bone minerals. The TM at 38.9ºC or 39.4ºC, however, promoted the improvement of most of the characteristics analyzed (p≤0.05). Thus, the constant modification profile of the TOC has been shown to harm the bone and locomotor characteristics, and the zootechnical performance of chickens at 42 days, with high temperatures being the most harmful. However, the intermittent profile using high and very high TCO positively influenced these characteristics, being, therefore, considered a viable and effective tool for the poultry industry.
