Recently during the course of a quality and food safety audit a 55-week old floor-housed flock was presented with extremely high mortality averaging 2% per week. Mortality was evenly spread among the four flocks of approximately 12,000 hens on the site. Birds were housed on slats over a pit and were provided with adequate feeding space, nipple drinkers, nest boxes and perches.
Mortality commenced at about 40 weeks of age and progressed through to the time of the examination at 55 weeks of age. The standard of management was high with no obvious problems other than low ambient temperature associated with severe winter weather. The contractor attributed mortality to cannibalism. Neither he nor the servicemen had submitted live or dead birds to a laboratory for examination.
The striking feature of freshly collected carcasses was that they consisted only of skin, feathers and skeletal remains. Birds were not pecking having been adequately beak trimmed but on observation it was evident that any recumbent hen was immediately attacked and “shredded” by aggressive birds using their toenails.
A few freshly dead birds were retrieved and examined. Predominant lesions comprised enlargement of the liver, peritonitis and purulent arthritis. These changes coupled with the pattern of mortality suggested a chronic bacterial infection.
Tissues were submitted to a diagnostic laboratory for examination. Since the farm had been used to supply fertile broiler hatching eggs prior to conversion to table eggs a provisional diagnosis of pasteurellosis was made which was confirmed by microbiological examination.
Administration of antibiotics was deferred as the flock was producing a branded specialty egg. Recommendations were provided to administer both E. coli and Pasteurella vaccines to replacement pullets in addition to the conventional vaccination program.
An intensive effort to suppress rodents was initiated, including sealing of doors to prevent entry of rats and mice which were evident in the facility.
This case demonstrates the need to recognize a deviation from normal livability and to submit representative samples for competent professional evaluation. Assuming that the problem was only cannibalism would have resulted in severe losses in the subsequent flock which would otherwise have not been protected against pasteurellosis.
Since many of the non-confined flocks in southern and southeastern states are housed in old broiler breeder units, the possibility exists that pasteurellosis persists in these facilities especially with evidence of chronic erosive mortality.
In this case, any sick or moribund bird was immediately attacked and killed, obscuring the actual cause of mortality.