title: Predictors of death and production performance of layer chickens in opened and sealed pens in a tropical savannah environment.
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%).
  
  
  CONCLUSIONS
  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.
authors.forename: Aminu
authors.initials: A
authors.lastname: Shittu
authors.forename: Abdullahi Abdullahi
authors.initials: AA
authors.lastname: Raji
authors.forename: Shuaibu A
authors.initials: SA
authors.lastname: Madugu
authors.forename: Akinola Waheed
authors.initials: AW
authors.lastname: Hassan
authors.forename: Folorunso Oludayo
authors.initials: FO
authors.lastname: Fasina
mesh_terms: D000818:Animals; D002645:Chickens / Q000502:physiology*; D004435:Eating; D005260:Female; D006358:Hot Temperature; D006799:Housing, Animal; D010058:Oviposition / Q000502:physiology*; D012307:Risk Factors; D012621:Seasons; D013312:Stress, Physiological; D016019:Survival Analysis; D014329:Tropical Climate