Productivity and mortality of laying hens in aviaries: a systematic review

Abstract

A systematic review of investigations on productivity, mortality and cannibalism of laying hens housed in aviaries is presented. In Part One we reviewed the studies that compared these parameters between laying hens housed in aviaries and in conventional cages. In Part Two we investigated the relative impact of strain, beak trimming and rearing condition on productivity and mortality in aviaries. The comparative analysis revealed that aviary hens consumed 3.0 % more food than caged hens, and food conversion was 6.7 % higher in aviaries than in cages. On the other hand, the mortality rate and cannibalism rate did not differ significantly between the two housing systems. The analysis of causes of variation in productivity, mortality rate and cannibalism rate in aviaries revealed a strong effect of strain. Beak trimming was associated with a reduced prevalence of cannibalism rates but had no effect on overall mortality. It also reduced egg weight and food consumption. Early access to litter during the rearing period had a positive effect on egg weight; egg mass, food conversion and mortality rate. In conclusion, we found a slightly reduced productivity of aviaries in relation to cages although the mortality rates and the prevalence of cannibalism did not differ between these housing systems. To further improve productivity and reduce mortality of hens housed in aviaries we recommend the choice of suitable strains and the implementation of improved rearing conditions including early access to litter. Keywords: systematic review; laying hens; aviary; housing system; productivity; mortality; strain; beak trimming; rearing IntroductionThe aviary housing system for laying hens was developed as an alternative to conventional battery cages. In various countries, this new housing system has been assessed with regard to animal welfare health and economic aspects, and these investigations often compared various parameters between hens housed in aviaries and conventional cages. To draw general conclusions, however, each of these studies was neither large enough nor covered a sufficiently wide range of conditions. We therefore made a systematic and quantitative review in which we combined the independent results of these studies. The aim of a systematic review is to produce an up-to-date and reproducible account of the present state of research. Moreover, according to Gates (2002), a quantitative review provides a considerable advance in scientific rigour over traditional narrative or "vote-counting" reviews.An early type of aviary was already operating in 1979 (Fölsch et al., 1983) and since then, the system was further developed. One of the aviary's best features is the construction of tiers and perches above the littered area, which allows the hens to move and get out of the way both horizontally and vertically. Furthermore, the spatial separation of the areas for eating, drinking, resting, foraging and dust bathing is considered as advantageous (Fröhlich, 1995). The use of the third dimension allows for housing additional...

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