Broiler stress responses to light intensity, flooring type, and leg weakness as assessed by heterophil-to-lymphocyte ratios, serum corticosterone, infrared thermography, and latency to lie

Abstract

Stress and leg weakness are detrimental to broiler production, health, and welfare. Traditional methods to evaluate stress may be stressful to the bird because they are invasive and require handling and restraint. Two studies examined the effects of light intensity and flooring on the following in broilers: 1) traditional methods for assessing stress using heterophil-to-lymphocyte ratios and serum corticosterone ( CORT) concentrations, 2) noninvasive measures of stress from infrared thermography ( IRT) eye and beak surface temperatures, and 3) latency-to-lie ( LTL) test times of birds tested individually and in groups of 5. Day-of-hatch male broiler chicks were placed into 6 pens (N = 120 chicks/pen). At 1 wk, pens were allocated to 3 light intensity treatments (2, 5, or 10 lux). At 4 wk, half of the birds from each pen were moved to a pen with wire flooring and the same light intensity. At 1, 4, 5, and 8 wk, blood samples were collected and IRT images of the heads of 5 clinically healthy broilers from each pen were captured. In study 2, IRT images of the heads of birds that became lame in the wire flooring pens were taken. There were no treatment effects on the LTL times of birds tested in groups or individually ( P > 0.05). On day 56 in study 1, birds on wire flooring had elevated heterophil-to-lymphocyte ratios and CORT concentrations ( P ≤ 0.002) and depressed IRT eye and beak temperatures ( P < 0.0001). In both studies, there were negative correlations between CORT concentrations and IRT beak surface temperatures ( P < 0.05). Lame birds had lower IRT eye and beak surface temperatures than sound birds ( P ≤ 0.004), and the IRT beak surface temperatures of lame birds were lower than their eye surface temperatures ( P = 0.004) in study 2. These studies indicate that the IRT surface temperatures of the eye, and more distinctly of the beak, can be used as sensitive noninvasive indicators of stress.