Abstract
Genetic improvement of muscle and meat quantity and quality of broiler chicken over the last 50 yr played a key role in broiler meat production. Thermal manipulation technique has been suggested to promote muscle growth and development. The combination of incubating temperature and timing or duration is very critical to determine the optimum protocol of thermal manipulation which underlines muscle growth improvement. Therefore, this study was to elucidate the optimum timing of thermal manipulation (TM) during embryogenesis on broiler pectoral and thigh muscle growth by assessing muscle growth parameter. This was achieved by analyzing the molecular expression levels of muscle insulin-like growth factor-1 (IGF-1), growth hormone (GH) and atrogin-1 during embryogenesis and d 35 post-hatch in addition to the measurement of sarcomeres length at d 35 post-hatch. One thousand, four hundred forty fertile eggs were randomly divided and equally into 5 groups. A control (no TM) and 4 thermal manipulated groups TM1, TM2, TM3, and TM4 that thermally subjected to 39°C for 18 h with 65% relative humidity daily during embryonic days (ED) ED7-11, ED 11-15, ED 15-18, and ED 7-18, respectively. IGF-1 and GH expression from early thermal manipulated chicks (ED7-11) were significantly higher in both pectoral and thigh muscles when compared to the control (P < 0.05). This improvement was in parallel with significant improvement in sarcomeres length of the same TM group on post-hatch d 35 (P < 0.05). On the other hand, Atrogin-1 expression was significantly lower in all treatment groups during post-hatch d 35 compared to the control (P < 0.05) (P < 0.05). It can be concluded that TM1 during ED 7-11 leads to improved pectoral and thigh muscles development without adversely affecting their performance. In addition, molecular and ultrastructure investigation of broiler chicken muscles can be used to predict meat quality and may be beneficial for commercial breeders to enhance broiler chicken growth and productivity.