Effects of housing system and cold stress on heterophil-to-lymphocyte ratio, fluctuating asymmetry, and tonic immobility duration of chickens.

The purpose of this study was to analyze the effect of housing system and cold stress on the heterophil-to-lymphocyte ratio, the fluctuating asymmetry, and the tonic immobility duration of chickens. In experiment 1, hens (n=120; 36 wk old) from 5 Spanish breeds and a White Leghorn population, which had been housed in pens with or without access to an outdoor area from 20 wk of age, were used. The effect of housing system on heterophil-to-lymphocyte ratio varied from breed to breed, differences between housing systems being significant (P<0.05) in 2 breeds. In these breeds (Red-Barred Vasca and Birchen Leonesa), heterophil-to-lymphocyte ratio was significantly greater in hens housed in deep litter. Housing effect was significant for the relative asymmetry of leg length (P<0.01), wattle length (P<0.05), and the combined relative asymmetry (P<0.05), the relative asymmetry of hens housed in deep litter being larger. There was no significant difference for the duration of tonic immobility between hens housed in deep litter or free range. Thus, hens with access to an outdoor area were less stressed than hens without access to an outdoor area, although the fearfulness was similar in both groups of birds. In experiment 2, cocks (n=120; 36 wk old) from 4 Spanish breeds, a synthetic breed, and the White Leghorn population, which had been housed in cages with or without a cold stress (0 to 10 degrees C) from 24 wk of age, were used. Cold x breed interaction was significant for heterophil-to-lymphocyte ratio (P<0.05), differences between cold-stressed and control birds being significant in 2 breeds. In these breeds (Red-Barred Vasca and Buff Prat), heterophil-to-lymphocyte ratio was significantly greater in cold-stressed birds. Cold stress effect was significant for the relative asymmetry of toe length (P<0.001) and the combined relative asymmetry (P<0.05), the relative asymmetry of birds with cold stress being larger than that of control birds. Thus, cold stress seriously negatively affects the welfare of cocks.