Reproductive Hormones During Molt: What Changes in Laying Hens?
Research Review
Molt and reproduction compete for a hen’s biological resources, but the relationship is not controlled by one “molt hormone.” Light, energy availability, the hypothalamic-pituitary-gonadal axis, the thyroid axis, ovarian follicles, and the oviduct all change as laying stops and feather replacement begins.
This evidence review begins with an open-access textbook chapter on hormonal control of egg formation and places it beside a recent primary study that measured reproductive hormones and reproductive tissues at four stages of induced molt.
Core Sources
Mishra, B., Sah, N., & Wasti, S. (2019). “Genetic and Hormonal Regulation of Egg Formation in the Oviduct of Laying Hens.” In Poultry—An Advanced Learning. DOI: 10.5772/intechopen.85011 — https://doi.org/10.5772/intechopen.85011.
Ma, P., Xue, F., Chen, J., et al. (2025). “Transcriptomic Insight into the Underlying Mechanism of Induced Molting on Reproductive Remodeling, Performance and Egg Quality in Laying Hen.” Poultry Science, 104(2), 104692. DOI: 10.1016/j.psj.2024.104692 — https://doi.org/10.1016/j.psj.2024.104692. Open-access full text — https://pmc.ncbi.nlm.nih.gov/articles/PMC11743122/.
Why This Research Matters
Online explanations often reduce molt to falling estrogen or rising thyroid hormone. That is too simple. In a laying hen, gonadotropin-releasing hormone supports pituitary release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH). FSH supports recruitment and development of smaller follicles. LH acts mainly on larger preovulatory follicles and participates in ovulation and steroid production. Estradiol supports follicular growth, yolk-precursor production in the liver, oviduct development, and egg-white protein synthesis. Progesterone from larger follicles contributes to the preovulatory LH surge.
When the ovary regresses during molt, these relationships change together. The important biological event is not merely a blood-test number; it is the coordinated pause and later rebuilding of the reproductive system.
Study Design
The 2025 primary study followed 240 Jingfen No. 6 laying hens, 380 days old, through four stages: pre-molt, molt, recovery, and a second peak-laying stage. The flock was divided into four replicates of 60 hens. The researchers recorded laying performance and egg quality, measured the ovary and oviduct, counted follicle classes, measured serum FSH, LH, estradiol, and progesterone, and sequenced RNA from ovarian and oviduct-magnum tissues.
This was a fasting-induced molt experiment. Hormone testing used four hens per time point, and there was no age-matched, continuously fed control group followed through the same period.
Key Findings
During the molt stage, the oviduct became smaller, large yellow follicles disappeared, and serum FSH, LH, estradiol, and progesterone declined compared with the pre-molt stage.
Reproductive hormone concentrations gradually increased during recovery as feeding resumed and reproductive tissues rebuilt.
Ovarian genes associated with steroid biosynthesis increased after molt and were positively associated with laying rate.
Changes in oviduct genes associated with collagen and laminin were correlated with albumen height and Haugh unit.
The results support a remodeling process in which reproductive tissues regress during the pause and later resume activity.
What the Results Do—and Do Not—Show
The study shows that reproductive regression and recovery are accompanied by coordinated changes in gonadotropins, ovarian steroids, follicles, tissue structure, and gene expression. It does not prove that a keeper should induce molt, that fasting is necessary for a natural molt, or that the same hormone pattern and timing will occur in every backyard hen.
An earlier study of 83-week-old Hy-Line hens also found that post-molt estrogen and progesterone were lower than pre-molt values even as laying performance improved, while LH and FSH were not significantly changed. That finding is a useful warning against treating one hormone concentration as a direct score of reproductive performance. Tissue sensitivity, receptor activity, yolk-precursor production, follicular uptake, timing, age, and study protocol all influence the result.
Practical Application for Poultry Keepers
A temporary drop in laying during molt is biologically consistent with ovarian and oviduct regression.
Feather loss by itself does not reveal a hen’s hormone concentrations or prove that a particular endocrine disease is present.
Light exposure, nutrition, age, health, and whether the molt is natural or induced can change the pattern.
Hormone data from induced commercial-layer protocols should not be used as instructions for backyard flock management.
Persistent illness, severe weight loss, abnormal abdominal enlargement, discharge, or failure to recover warrants veterinary evaluation rather than an assumption that “it is just molt.”
Limits of the Evidence
The main experiment used one commercial Chinese layer line and a fasting-induced protocol. Hormones were measured in only four hens per time point. Because the same production system was not compared with an age-matched, non-molted control, changes cannot be separated perfectly from age, time, feed withdrawal, and molt. Transcriptomic associations can identify candidate pathways but do not by themselves prove that a gene caused the production response. Welfare conclusions also cannot be drawn from production and molecular outcomes alone.
Poultry Nerds Takeaway
During molt, the laying hen’s reproductive system does not simply “switch off” because one hormone falls. Ovarian follicles, the oviduct, FSH, LH, estradiol, progesterone, and gene expression change as part of a coordinated regression-and-recovery process. The science helps explain why laying pauses, but it does not justify fasting-based molt programs or turn hormone measurements into a simple management recipe.
Continue the Research Cluster
Feather anatomy and composition in chickens — /research-library/chicken-feather-anatomy-composition
How feathers harden: Alibardi’s protein study explained — /research-library/alibardi-feather-proteins-cornification
Browse the Poultry Nerds Research Library — /research-library
Research Review Notice: This article summarizes an open-access scientific chapter and peer-reviewed primary research. It is an original review written by Poultry Nerds and is not a reproduction of either source. Results from fasting-induced commercial-layer studies should not be generalized to natural molt, other breeds, or individual backyard hens without appropriate evidence.