Transcriptome and histologic analysis of cardiac differences between modern broiler and heritage chickens
University of Delaware
This project focuses on characterizing differentially expressed genes in the left ventricle of the heart, comparing the Heritage chicken line, selectively bred for meat production until the 1950's, and Ross 708, a modern fast-growing broiler line, during normal post-hatch growth at 6, 21, and 42 days of age. Since Ross 708 broilers have a reduced normalized heart size and increased susceptibility to heart failure compared to Heritage birds, this research may offer insight into the pathological consequences of selection for rapid growth on the heart, and may further explain the development of left ventricular enlargement that is seen in the modern broiler. Most differences in gene expression are observed at 21 days post hatch, in genes related to collagen fiber remodeling in the extracellular matrix, inflammatory cytokines, and expression of developmental proteins in Ross 708 compared to Heritage. This may indicate a mechanism for coping with pressure or volume overload due to the increased body size and slower rate of growth in the heart in Ross 708. Histologic analysis of cardiac tissue between groups shows that there is no significant increase in myofiber diameter between 21 and 42 days post hatch within the Ross 708 line, but average myofiber diameter is larger in Heritage than Ross 708 at 28 and 42 days post hatch. Some lesions are observed in the myocardium when transverse sections of heart stained with hematoxylin and eosin are analyzed, but there was no evidence of ascites or heart failure in birds from either line. Slightly thickened interstitial collagen is observed in the Ross 708 line at 21, 28 and 42 DPH compared to the Heritage line when transverse sections of the myocardium are compared with a trichrome stain.