The influence of genetic strain on fear and anxiety responses of laying hens housed in a cage-free environment

Abstract

Cage-free environments provide more behavioral opportunities for hens than cages, but fear responses in such open housing can lead to injuries and challenging human-animal interactions. This study evaluated the impact of genetic strain on fear and anxiety responses in two brown and one white genetic strain of laying hens: Hy-Line Brown (HB), Bovan Brown (BB), and H&N White (HN). Hens were assessed at the start of lay and peak lay through the inversion and attention bias tests, along with thermal imaging and core body temperature measurements to assess stress-induced hyperthermia. During the inversion test, HB hens performed significantly more wing flaps than other strains (p=0.012), while BB hens exhibited more vocalizations than HN hens (p=0.0041). Thermal imaging revealed that at the start of lay, HB and HN hens had higher maximum comb temperatures than BB hens (p<0.0001), but HB hens had lower temperatures at peak lay (p=0.027). BB and HN hens had higher core body temperatures at 4- and 5-minutes post-inversion (p<0.0001). In the attention bias test, HB and BB hens were more likely to resume eating and showed increased head bobbing as they aged, whereas HN hens were less likely to resume eating but maintained high head bobbing (p=0.017; p=0.00056). BB hens had the lowest average eye and maximum comb temperatures 3.5 to 4.5 min post-startle at the start of lay (p<0.05), white HN hens had the highest average eye and comb temperatures (p<0.0001) and higher average eye temperatures than BB at peak lay (p=0.026). Finally, HN hens had higher core body temperatures than HB hens at both the start of lay and peak lay (p=0.041; p=0.046). These results indicate that brown and white strains differ in their responses to fear and anxiety, with brown strains being more behaviorally responsive and white strains showing greater physiological stress. These strain-specific coping mechanisms provide insight into how hens may react to stressors in cage-free environments, aiding in strain selection for producers.