Enzootic outbreak and spontaneous regression of keratoacanthomas in a commercial layer flock

This paper reports an enzootic outbreak and spontaneous regression of keratoacanthomas among adult layer hens with lesions on the skin of the legs. The observations were performed in a flock of 55,000 commercial layers (50,000 Lohmann White and 5,000 Lohmann Brown). At the age of 30 weeks, Lohmann White layers exhibited a number of growths (at an average of 60 hens per week, representing 0.1% of the flock) in the region of leg toes on a daily basis over 28 weeks that regressed during the remaining flock production period. Gross and histological investigations identified the lesions as keratoacanthomas. PCR analysis was negative for avian leukosis virus (ALV) and reticuloendotheliosis virus (REV). The present investigations have revealed an unusual case: this is the first report on an enzootic outbreak of multiple keratoacanthomas in commercial layers. The results of the aetiological investigations do not show a relation to any infectious agent or a chemical-toxic cause. The abnormal invasion of keratinocytes from the stratum corneum leading to neoplasms in this case coincides with the phase of peak laying capacity which is in fact a stress factor and might be regarded as a provocative moment.