Extending laying hens’ productive lifespan by molting: a pilot on-farm study and test of assessment methods with focus on functional traits and keel bone health

This study investigated potential methods to test the effects of induced molting on performance, health, and welfare traits in two mobile-housed end-of-lay flocks on individually marked hens under practical conditions. Flock 1 consisted of 124 dual-purpose Coffee & Cream hens managed organically with continued free-range access during molting. Flock 2 included 162 Lohmann Brown hens under conventional conditions without free-range access during molting. Molting protocols differed markedly in duration and severity. Molting was induced by restricting feed and light. Health, performance, and keel bone traits were assessed before, during, and after molting using individual marking, radiography, egg and feed analyses, and endoparasite diagnostics. Laying performance declined during molting in both flocks and partially recovered afterwards (flock 1: from 54% to 30% to 39%; flock 2: from 89% to 0% to 65%). Egg quality parameters improved post-molt in both flocks, suggesting recovery of reproductive tract function. Body weight decreased throughout molting and increased significantly thereafter in both flocks, indicating physiological recovery. However, keel bone fracture prevalence increased significantly from before to after molting in both flocks, despite stable or improved bone mineral density (BMD). Comb injuries increased significantly in flock 2 post-molt, likely due to abrupt feed withdrawal and lack of free-range access. Conversely, flock 1, managed under a gradual molting protocol, exhibited calmer behavior and general improvement in integument scores. Feed analyses revealed presumably suboptimal calcium-to-phosphorus (Ca:P) ratios in both flocks, which may have limited skeletal recovery. Because molting occurred in different seasons, photoperiod and climatic conditions may have moderated cohort responses and should be interpreted as contextual field effects rather than causal treatment differences. This study highlights that molting outcomes are associated with flock condition and the applied molting protocol. Furthermore, the methods of individual marking and X-raying of hens proved to be applicable and informative, provided that suitable leg rings are used and consistent X-ray settings are maintained. However, a sufficiently large sample size is required to compensate for potential losses, and it should be taken into account that hens are particularly sensitive during the molting period.