The effect of genotype on tonic immobility and walking ability in broiler chickens

Abstract

This study was conducted to determine the changes in fear stress level and walking ability at 6 weeks of age in broiler pure lines with different growth levels and to determine the relationship between them.  Five ANADOLU-T broiler pure lines (A1, A2 and A3 dam lines and B1 and B2 sire lines) with different growth characteristics and ROSS-308 hybrids were used in the experiment. Individual body weight was determined in 90 broilers of each genotype and tonic immobility (TI) duration, number of TI inductions and gait score traits were determined in 4 female and 4 male broilers at 6 weeks of age. The analysis of traits was performed using two-way analysis of variance and the main effects of genotype and sex were included. Kendall's tau b correlation was used to determine the relationships among the traits. The body weight was significantly different among the genotypes (P<0.001).  ROSS-308 hybrid (3279.5 g) had the highest body weight followed by B1 (3035.2 g), B2 (2905.8 g), A2 (2560.8 g), A1 (2548.9 g) and A3 lines (2461.7 g). In addition, males (3176 g) were heavier than females (2551.1 g) (P<0.001). Genotype had no effect on the duration of TI and the number of TI inductions, but females had higher values than males (P<0.001). Males (262.5 s) showed longer TI duration than females (145.7 s) (P<0.05). Genotype and sex effects on gait score were significant (P<0.001). While walking ability was the worst in B1 line, it was the best in A1 line and female birds showed better walking ability than males. Significant correlations were determined between body weight and number of TI inductions (r=-0.36), TI duration (r=0.22) and walking ability (r=0.43). As a result of the study, higher body weight had a negative effect on walking ability in broiler chickens at 6 weeks of age, while stress level due to physiological compulsion was higher and walking ability was lower in male broilers. In broiler breeding, selection of birds with high resistance to stress factors and gait problems, especially in male individuals, may provide permanent solutions for a more profitable and sustainable production.