Data from: Implications for welfare, productivity and sustainability of the variation in reported levels of mortality for laying hen flocks kept in different housing systems: a meta-analysis of ten studies.

Data from ten sources comprising 3,851 flocks were modelled to identify
variation in levels of mortality in laying hens. The predicted increase
with age was curvilinear with significant variation between the seven
breed categories. Mortality was higher in loose housing systems than in
cages and variable within system, confirming previous reports. Cumulative
mortality (CM) was higher in flocks with intact beaks (?2 = 6.03; df 1;
p=0.014) than in those with trimmed beaks. Most data were available for
free-range systems (2,823 flocks), where producer recorded CM at 60-80
weeks of age averaged 10% but with a range from 0% to 69.3%. Life cycle
assessment showed that the main effect of increased levels of hen
mortality is to increase the relative contribution of breeding overheads,
so increasing environmental burdens per unit of production. Reducing CM to
levels currently achieved by the 1st quartile could reduce flock
greenhouse gas emissions by as much as 25%. Concurrently this would
enhance hen welfare and better meet the expectation of egg consumers. More
research to understand the genetic x environment interaction and detailed
records of the causes of mortality are required so that improved genotypes
can be developed for different systems and different breeds can be better
managed within systems.