Breed-dependent susceptibility to acute sound exposure in young chickens.

Commercially available chickens fall into two categories: egg layers and broilers. Durham et al. (Hear. Res. 166 (2002) 82-95) showed that despite similar noisy living environments, cochleae of most adult broilers show extensive damage, while cochleae of adult egg layers are largely normal. This finding suggests that egg layers and broilers differ in their susceptibility to noise damage. Here, we evaluate breed differences in susceptibility to acoustic trauma. Young egg layers and broilers (10-17 weeks) were exposed to a 1500Hz pure tone (120dB SPL; 24h) and killed 24 or 72h later. Cochleae were prepared for scanning electron microscopy and photomicrographs of the cochlear surface were used to determine location and severity of damage. Cochleae were grouped based upon damage severity (moderate or severe). While location and area of damage were similar between both breeds at each recovery time, cochlear damage at 72h was more extensive than at 24h. We found no quantitative breed differences within either damage category or recovery time. However, more egg layers (25/27) than broilers (16/32) displayed severely damaged cochleae. Our findings conflict with those reported by Durham et al. (2002). Our results identify a breed-dependent difference in susceptibility to acute sound exposure, with young egg layers displaying increased sensitivity.