Abstract:
BACKGROUND: Layer chickens are exposed to high risks of production losses and mortality with impact on farm
profitability. The harsh tropical climate and severe disease outbreaks, poor biosecurity, sub-minimal vaccination and
treatment protocols, poor management practices, poor chick quality, feed-associated causes, and unintended
accidents oftentimes aggravate mortality and negatively affect egg production. The objectives of this study were to
estimate the probability of survival and evaluate risk factors for death under different intensive housing conditions
in a tropical climate, and to assess the production performance in the housing systems.
RESULTS: Daily mean mortality percentages and egg production figures were significantly lower and higher in the
sealed pens and open houses (P < 0. 001) respectively. The total mean feed consumption/bird/day was similar for
the open sided and sealed pens but the mean feed quantity per egg produce was significantly lower in the sealed
pens ((P < 0.005). Seasons differently impacted on mortality with the hot-dry season producing significantly higher
risk of mortality (61 times) and reduced egg production. Other parameters also differed except the egg production
during the cold-dry season. Layers in sealed pens appear to have higher probability of survival and the Kaplan-Meir
survival curves differed for each pen; ≥78 weeks old layer have higher probability of survival compared with the
younger chickens and the 19–38 weeks age category are at highest risk of death (P < 0.001). The hazard-ratio for
mortality of layers raised in sealed pens was 0.568 (56.8%).
CONCLUSION: Reasons for spiked mortality in layer chickens may not always be associated with disease. Hot-dry
climatic environment is associated with heat stress, waning immunity and inefficient feed usage and increase
probability of death with reduced egg production; usage of environmentally controlled building in conditions
where environmental temperature may rise significantly above 25°C will reduce this impact. Since younger birds
(19–38 weeks) are at higher risk of death due to stress of coming into production, management changes and
diseases, critical implementation of protocols that will reduce death at this precarious period becomes mandatory.
Whether older chickens’ better protection from death is associated with many prophylactic and metaphylactic
regimen of medications/vaccination will need further investigation.
