Interesting semi-relevant factoid from some literature review I'm doing for a class:
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https://www.mdpi.com/2076-2615/10/2/177 Bestman et. al.
This is from a research study done in the Netherlands on predation pressures on organic* and free-range egg farming. So expectations of productivity, even in this setting, is still only 78 weeks (18 months) to 82 weeks (about 19 months.) As the lowest number of hens on these farms was about 6,000, I doubt that they remain alive after this age, heading off to pet-food and chicken stock producers. Additionally, one of the measures studied was number alive when reaching the slaughterhouse.
@BDutch and
@Skyeknight may have more information on their fates.
Relevant to this discussion in that large-scale egg production and its accompanying economics is definitely not limited to caged birds.
*The study differentiated between "organic" and "free-range" while yet defining both groups as free-range. I am guessing that the difference is for organic certification purposes regarding feed, etc., but otherwise with essentially identical cultivation practices.