Causes of disease in two commercial flocks of laying hens.

Laboratory examination of all birds that were culled or died during an eight-month period in two commerical laying flocks was performed to reveal the causes of disease and their prevalence. The average weekly total of diseased birds was greater in one flock (60-69) than the other (27-37). This resulted mainly from a high incidence in the former flock of leucoses and sarcomas, although losses due to fatty liver syndrome, prolapse and cannibalism and cage layer fatigue were also marginally greater in this flock than the second. Haemangiomas occurred more frequently in the flock with the higher disease level. A total of 273 hens of the 2,000 examined from this flock had single or multiple haemangiomas. Special features of the major causes of disease were outlined and discussed. A conclusion made from this study was that histopathological examination is necessary for accurate diagnosis of avian tumours.