Abstract
As a result of genetic selection, the modern broiler is more efficient, higher yielding, and faster growing than the bird of the 1950s. Unfortunately, as a result of improvement in growth rate, the modern broiler has the potential to struggle under heat stress conditions. The present study evaluates 3 different random bred populations and a common ancestor under both a thermal neutral and heat stress conditions after a 54-D grow-out period. The lines used in this study included the Athens Canadian Random Bred (ACRB), a 1995 Random Bred (95RAN), a 2015 Random Bred (MRB), and a Junglefowl (JF). Male chicks (n = 150/line) were placed by line in environmentally controlled chambers. An 8-h daily cyclic heat stress (36°C) was applied to half of the chambers beginning on day 28 (HS) and lasting until processing at day 55, while the remaining chambers remained thermal neutral (TN) at 26°C. Dock weights and carcass weights were lower in the HS-95RAN and HS-MRB, compared to their TN counterparts, while the ACRB and JF had no difference in dock and carcass weights regardless of environmental condition. The MRB line had the highest breast yield (27.79%) while the JF (12.79%) and ACRB (12.42%) had the lowest. The 95RAN line had the highest abdominal fat percentage (2.83%) while the MRB line had the lowest moisture uptake during chill. The HS exposure lowered overall breast yield and breast pH at 15 min and 4 h postmortem but did not have an impact on color (L∗) or 24 h breast drip loss. The MRB was scored for both woody breast and white striping. The TN-MRB group had a higher incidence of moderate and severe woody breast and white striping than the HS-MRB group. Based on the results of this study, it appears that HS has a greater negative impact on the higher yielding lines (MRB and 95RAN) than the ACRB and JF and that clear line differences exist between the random bred lines and their common ancestor.