Physiological Responses to Heat Stress in Three Chicken Lines

Heat stress is one of the most important environmental factors negatively impacting poultry production and health. Genetics are an important contributor in responding to heat stress. Three different chicken lines, two genetically distinct highly inbred lines (Leghorn and Fayoumi) and one commercial egg-laying line (Hy-Line Brown), were characterized for phenotypic differences in response to heat stress. At 14d of age, birds were treated at 35C with 60% relative humidity or at 22C as a control. For the heat-treated group, birds were inoculated at 21d with 10⁷ EID50 Newcastle disease virus (NDV) La Sota strain to investigate the effects of both heat stress and NDV infection. Body temperature and blood components were measured using the iSTAT at four stages: Pre-heat, Acute Heat, Chronic heat 1 and 2 (AH, CH1, CH2, at 4h, 7d and 10d post heat treatment, respectively). Body temperature differences between treated and non-treated group were significant at CH2 for both inbred lines and at CH1 in Hy-Line. Most iSTAT parameters were significantly changed with heat treatment in Fayoumis and Hy-Line birds, but not in Leghorns. The heat-resilient Fayoumis had low sodium and glucose levels, high pH and low Hct and Hb. Physiological measurements of Hy-Line birds were more diverse and altering directions or magnitude of these measurements were mostly opposite to Fayoumi birds. This study provides a foundation for characterizing genetic resistance to heat stress in chickens and the biomarkers of physiological responses could serve as potential candidates for predicting heat tolerance.