Early post-hatch thermal stress effects on broiler muscle development and performance

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In broilers, the immediate post-hatch handling period exposes chicks to cold or hot thermal stress, with potentially harmful consequences to product quantity and quality that could threaten poultry meat marketability as a healthy, low-fat food. This lower performance includes adverse effects on muscle growth and damage to muscle structure (e.g., less protein and more fat deposition). A leading candidate for mediating the effects of thermal stress on muscle growth and development is a unique group of skeletal muscle cells known as adult myoblasts (satellite cells). Satellite cells are multipotential stem cells that can be stimulated to follow other developmental pathways, especially adipogenesis in lieu of muscle formation. They are most active during the first week of age in broilers and have been shown to be sensitive to environmental conditions and nutritional status. The hypothesis of the present study was that immediate post-hatch thermal stress would harm broiler growth and performance. In particular, growth characteristics and gene expression of muscle progenitor cells (i.e., satellite cells) will be affected, leading to increased fat deposition, resulting in long-term changes in muscle structure and a reduction in meat yield. The in vitro studies on cultured satellite cells derived from different muscle, have demonstrated that, anaerobic pectoralis major satellite cells are more predisposed to adipogenic conversion and more sensitive during myogenic proliferation and differentiation than aerobic biceps femoris cells when challenged to both hot and cold thermal stress. These results corroborated the in vivo studies, establishing that chronic heat exposure of broiler chicks at their first two week of life leads to impaired myogenicity of the satellite cells, and increased fat deposition in the muscle. Moreover, chronic exposure of chicks to inaccurate temperature, in particular to heat vs. cold, during their early posthatch periods has long-term effects of BW, absolute muscle growth and muscle morphology and meat quality. The latter is manifested by higher lipid and collagen deposition and may lead to the white striping occurrence. The results of this study emphasize the high sensitivity of muscle progenitor cells in the early posthatch period at a time when they are highly active and therefore the importance of rearing broiler chicks under accurate ambient temperatures. From an agricultural point of view, this research clearly demonstrates the immediate and long-term adverse effects on broiler muscling and fat formation due to chronic exposure to hot stress vs. cold temperatures at early age posthatch. These findings will aid in developing management strategies to improve broiler performance in Israel and the USA. BARD Report - Project4592 Page 2 of 29