title: Breed differences in cochlear integrity in adult, commercially raised chickens.
abstract: Two types of chickens are commercially available. Broiler birds are bred to develop quickly for meat production, while egg layers are bred to attain a smaller adult size. Because we have observed breed differences in the response of central auditory neurons to cochlear ablation in adult birds [Edmonds et al. (1999) Hear. Res. 127, 62-76], we examined cochleae from the two breeds for differences in integrity. We evaluated cochlear hair cell structure using scanning electron microscopy and cochlear hair cell function using distortion product otoacoustic emissions (DPOAEs) and the auditory brainstem response. We observed striking breed differences in cochlear integrity in adult but not hatchling birds. In adult broiler birds, all cochleae showed damage, encompassing at least the basal 29% of the cochlea. In 15 of 18 broiler ears, damage was observed throughout the basal 60% of the cochlea. In contrast, cochleae from egg layer adults were largely normal. Two thirds of egg layer ears showed no anatomical abnormalities, while in the remainder cochlear damage was seen within the basal 48% of the cochlea. DPOAEs recorded from egg layer birds showed loss of high frequency emissions in every ear for which the cochlea displayed anatomical damage. Average sound pressure levels in both commercial facilities were 90 dB, suggesting these two breeds may exhibit differential susceptibility to noise damage.
authors.affiliation: Department of Otolaryngology and the Smith Mental Retardation Research Center, University of Kansas Medical Center, 3901 Rainbow Boulevard, Kansas City, KS 66160-7380, USA. ddurham@kumc.edu
authors.forename: Dianne
authors.initials: D
authors.lastname: Durham
authors.forename: Debra L
authors.initials: DL
authors.lastname: Park
authors.forename: Douglas A
authors.initials: DA
authors.lastname: Girod
mesh_terms: D000375:Aging / Q000473:pathology / Q000502:physiology; D000818:Animals; D001947:Breeding; D002645:Chickens / Q000033:anatomy & histology* / Q000502:physiology*; D016057:Evoked Potentials, Auditory, Brain Stem; D005260:Female; D006198:Hair Cells, Auditory / Q000002:abnormalities / Q000502:physiology / Q000648:ultrastructure; D006317:Hearing Loss, Noise-Induced / Q000473:pathology / Q000503:physiopathology; D008855:Microscopy, Electron, Scanning; D017084:Otoacoustic Emissions, Spontaneous; D012038:Regeneration; D013045:Species Specificity