Abstract
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 (χ2 = 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 is required so that improved genotypes can be developed for different systems and different breeds can be better managed within systems.
Highlights
Conventional cages have been outlawed in Europe since 2012 (EU Directive 1999/74/EC)
All variables show highly significant associations with cumulative mortality (CM), which increased with age; decreased with flock size; was highest in flocks of intact beaked birds and organic flocks; and varied with both housing system and breed
In the final model, which explained 84.9% of the variation in the dataset, and included 3,132 data points, CM increased with age in a quadratic relationship (χ2 = 459.9; df 2; p
Summary
Conventional cages have been outlawed in Europe since 2012 (EU Directive 1999/74/EC). In a larger survey [7] of UK data from 1,486 flocks in 2009 we found that mortality rates by the end of lay in free-range flocks (mean: 9.5%) were significantly greater than in flocks kept in cages (both furnished and conventional; mean: 5.4%). These figures were based on producer records on the Food Chain Information form completed a median of 7 days before slaughter, slightly underestimating the final cumulative mortality on farm
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