SUMMARY
To improve hen welfare, several studies have investigated various environmental enrichments that suit different laying hen production systems. The positive results of these studies can enable such environmental enrichments to be utilized in commercial laying hen production. This paper reviewed the effects of environmental enrichments in different laying hen production systems on hen welfare and egg quality. The successfully proven environmental enrichments in free-range production system include forage, shelterbelt, and artificial shade in outdoor area and novel objects and H-shaped perching structures in indoor. These are associated with increased range use that positively affects hen welfare. In aviary system, perches, and litter materials (e.g., straw, sand) as environmental enrichments are linked to improved behavioral expression, reduced stress, and enhanced immune system. Under the litter system, environmental enrichment with substrates (e.g., pecking stones, alfalfa blocks, silage, straw, barley) has been found to increase the foraging behavior of laying hens. This reduces severe feather pecking thus, improving the plumage condition of hens. Although the effects of environmental enrichments on hen welfare have been assessed and scientifically proven in the reviewed studies, significant progress of their impact on egg quality traits has not been reported. The studies have shown that environmental enrichments have no significant effect on egg quality traits. Also, appropriate pasture or plant species as environmental enrichments in free-range production system in relation to hen welfare and egg quality have not been identified. Therefore, it is important to continue studies on environmental enrichments while emphasizing their influence on egg quality since it is a major performance trait in the egg industry. In addition, there is a need for studies to identify ideal pasture or plant species for free-range production system that positively affects hen welfare and egg quality.