HEALTH OF LAYING HENS IN AN AVIARY SYSTEM OVER 5 BATCHES OF BIRDS

Mortality and health were studied in laying hens kept in an aviary sys tem on a practical scale. All manage ment inputs were done by universi ty staff. Five batches of birds (trials) during a period of 6 years wi th approximately 4700 birds per trial were included in the study. The aviary was a three-tiered ''Marielund'' system divided into 4 pens. Th ree hybrids, reared on litter with access to perches, were used; Lohma nn Selected Leghorn (LSL), Lohmann Brown (LB) and an experimental cros s (SLU-1329). The hens were not beak-trimmed. The stocking density was 17 hens/m(2) ground floor. Mortality varied between pens and between batches, ranging from normal rates of 3.4% to 7.8%, except in LSL in T rial 2 and LB in Trial 3 where it was much higher (15.6% and 20.9%, re spectively). The dominating causes of total mortality were salpingitis and cannibalism. Coccidiosis and lymphoid leucosis contributed signif icantly to mortality in Trial 2. An infestation with fowl mites (Derma nyssus gallinae) occurred in Trial 1. Feather loss was most severe in LB. Keel bone deviations were recorded at increasing levels by age. Fo ot abscesses occurred more frequently at 35 weeks than at 55 weeks. LS L was more severely affected than LB and SLU-1329.