During the transition to egg production, laying hens’ kidneys undergo a major shift in function around weeks 20-21 of life that makes them more efficient at managing calcium and phosphorus minerals. Research shows that genes controlling mineral transport in the kidney become increasingly active as birds mature, reaching peak activity by week 23 when egg laying begins. This adaptation allows hens to maintain the high blood calcium levels necessary for producing strong eggshells.
When young female chickens grow up and start laying eggs, their bodies go through major changes to handle all the calcium and phosphorus needed for eggshells. Researchers studied how chicken kidneys adapt during this transition by tracking gene activity and mineral levels in the blood. According to Gram Research analysis, the kidneys of laying hens shift their function around weeks 20-21 of life to become more efficient at managing minerals, which helps support the high calcium levels needed for strong eggshells. This research helps us understand how animals’ bodies adjust to meet new demands during major life changes.
Key Statistics
A 2026 study of 140 laying hens found that genes responsible for active calcium and phosphorus transport in the kidney showed reduced activity in immature birds but increased significantly by week 23 of age, coinciding with the onset of egg production.
Research examining 84 kidney tissue samples from laying hens revealed that genes involved in kidney filter structure showed their lowest activity around week 20 of life, then increased afterward, indicating active kidney restructuring during the transition to egg laying.
A study of two chicken breeds (Lohmann Selected Leghorn and Lohmann Brown) demonstrated that laying hens actively increase calcium and phosphorus loss in their urine before beginning egg production, suggesting the kidneys prepare for the shift to maintaining high blood mineral levels.
Research tracking hens from weeks 16 to 23 of age identified weeks 20-21 as a critical transition period when laying hens’ kidneys shift to enhanced mineral efficiency that supports the high blood calcium needed for eggshell calcification.
The Quick Take
- What they studied: How chicken kidneys change and adapt their function as young hens mature and begin laying eggs, particularly focusing on how they handle calcium and phosphorus minerals.
- Who participated: Two breeds of young female chickens (Lohmann Selected Leghorn and Lohmann Brown) were tracked from weeks 16 to 23 of age. Blood samples came from 140 birds and kidney tissue samples from 84 birds during different stages of maturation and the start of egg production.
- Key finding: Between weeks 20 and 21 of life, laying hens’ kidneys undergo a significant shift that makes them better at managing minerals. This change helps maintain the high calcium levels in the blood that are necessary for producing strong eggshells.
- What it means for you: While this research focuses on chickens, it reveals how animal bodies adapt to major physiological changes. Understanding these mineral management processes could inform better nutrition strategies for laying hens in farming, potentially improving egg quality and hen health. The findings are specific to poultry and don’t directly apply to human nutrition.
The Research Details
Researchers tracked two breeds of young female chickens as they matured from weeks 16 to 23 of age. During this time, the birds were fed three different diets: a developer diet for weeks 14-16, a pre-layer diet for weeks 16-17, and a layer diet for weeks 17-23. The layer diet contained high amounts of calcium to prepare the birds for egg production. Scientists collected blood samples from 140 birds and kidney tissue samples from 84 birds at different time points. They then analyzed the kidneys to see which genes were active and how their activity changed over time. They also measured calcium and phosphorus levels in the blood to understand how the kidneys were handling these minerals.
By studying gene activity in the kidneys during this critical transition period, researchers could identify exactly when and how the kidneys adapt to handle the demands of egg production. This approach is more detailed than just measuring mineral levels in the blood because it shows the biological mechanisms driving those changes. Understanding these mechanisms helps scientists and farmers optimize nutrition and care for laying hens.
This study examined a reasonable sample size of birds from two different breeds, which strengthens the findings. The researchers measured both gene expression and blood mineral levels, providing multiple types of evidence. The study tracked birds over a specific time period with controlled diets, allowing researchers to observe changes as they happened. However, the study was conducted in a controlled research setting, so results may differ slightly in real farm conditions.
What the Results Show
Genes responsible for actively transporting calcium and phosphorus in the kidney showed a clear pattern: they were less active in young, immature birds but became increasingly active as the birds approached egg-laying age, reaching peak activity by week 23. This timing suggests the kidneys are preparing to handle the mineral demands of egg production. Genes involved in maintaining the structure and function of kidney filters also showed reduced activity in immature birds, with the lowest levels around week 20, then increased activity afterward. This indicates the kidneys are physically restructuring themselves during this transition. Genes involved in responding to hormones that regulate mineral balance showed altered activity patterns, suggesting the kidneys become less responsive to certain hormonal signals as birds prepare for high egg production. The researchers found evidence that laying hens actively increase the loss of calcium and phosphorus in their urine before they start laying eggs, which may help their bodies prepare for the shift to maintaining high blood calcium levels needed for eggshell formation.
The study identified that the most dramatic changes in kidney function occur between weeks 20 and 21 of life, marking a critical transition point. Both chicken breeds showed similar patterns, suggesting these adaptations are consistent across different genetic lines. The timing of these changes correlates with when hens begin producing eggs, indicating the kidneys’ adaptations are coordinated with reproductive maturation. The research shows that the high calcium diet fed to pre-laying hens triggers specific kidney responses, demonstrating that nutrition directly influences how the kidneys adapt.
This research builds on earlier studies showing that laying hens maintain unusually high calcium levels in their blood to support eggshell production. Previous work identified that the kidneys play a key role in this process, but this study provides new detail about exactly which genes are involved and when they become active. The findings confirm that kidney adaptation is an active, coordinated process rather than a passive response to dietary changes. This work adds to our understanding of how animals’ bodies prepare for major physiological demands like reproduction.
The study was conducted in a controlled research environment with specific diets and bird breeds, so results may not perfectly match what happens in all farm settings or with different chicken breeds. The researchers focused on two specific chicken breeds, so findings may not apply equally to all laying hen varieties. The study measured gene activity at specific time points rather than continuously, so some changes happening between measurement dates may have been missed. The research doesn’t explain all the details of how hormonal signals coordinate these kidney changes, leaving some questions about the complete biological picture unanswered.
The Bottom Line
For poultry farmers, these findings suggest that providing appropriate pre-layer diets several weeks before hens begin laying eggs allows their kidneys time to adapt properly, which may improve egg quality and hen health. The research supports feeding high-calcium diets starting around week 16-17 of age to match the kidney’s natural adaptation timeline. Farmers should monitor hens closely during weeks 20-21 when the most dramatic kidney changes occur. These recommendations have moderate to strong support from this research, though additional studies in farm settings would strengthen confidence in their practical application.
Poultry farmers and nutritionists should pay attention to these findings when planning feeding programs for laying hens. Veterinarians treating laying hens may find this information useful for understanding mineral-related health issues. Researchers studying animal physiology and mineral metabolism will find this work relevant. People interested in sustainable and efficient egg production may benefit from understanding how proper nutrition supports hen health. This research is specific to chickens and doesn’t apply to other animals or to human nutrition.
The kidney adaptations described in this study occur over several weeks, with the most significant changes happening between weeks 20 and 21 of age. Farmers implementing improved feeding programs based on these findings would likely see benefits in egg quality and hen health within the first few weeks of lay, though optimal results may take several weeks to fully appear as the hens’ bodies fully adjust to egg production.
Frequently Asked Questions
What happens to a chicken’s kidneys when it starts laying eggs?
A chicken’s kidneys undergo significant changes between weeks 20-21 of life to better manage calcium and phosphorus minerals. Genes controlling mineral transport become more active, and the kidneys restructure to maintain the high blood calcium levels needed for producing eggshells.
Why do laying hens need so much calcium?
Laying hens need high blood calcium levels to produce strong eggshells. Each egg requires substantial calcium for the shell, so hens’ bodies maintain elevated calcium in their blood to support continuous egg production. The kidneys adapt to help maintain these high levels.
When should farmers switch young chickens to layer feed?
Research suggests transitioning to pre-layer diet around week 16 and switching to full layer diet by week 17 of age. This timing allows the kidneys to adapt properly before egg production begins around week 20-21, potentially improving egg quality and hen health.
How do chicken kidneys prepare for egg production?
Chicken kidneys prepare by gradually increasing the activity of genes that transport and manage minerals. They also restructure their filter systems and become less responsive to certain hormonal signals, allowing them to maintain the high blood calcium levels required for eggshell formation.
Do all chicken breeds adapt to egg production the same way?
This study examined two chicken breeds and found similar adaptation patterns in both, suggesting the process is consistent across different genetic lines. However, some variation may exist in other breeds, and more research would help confirm whether all laying hen varieties follow the same timeline.
Want to Apply This Research?
- For poultry farmers using a nutrition tracking app, record the specific age of hens when transitioning between developer, pre-layer, and layer diets. Track egg production start date and early egg quality metrics (shell strength, size) to correlate with the timing of diet changes and kidney adaptation phases.
- Implement a feeding schedule that aligns with the kidney adaptation timeline: transition to pre-layer diet by week 16, switch to layer diet by week 17, and monitor hens closely during weeks 20-21 when the most significant physiological changes occur. Use the app to set reminders for diet transitions and to log observations about hen health and egg quality during these critical periods.
- Create a long-term tracking system that records diet type and timing, hen age, egg production onset, and egg quality metrics. Compare these data across flocks and seasons to identify patterns and optimize feeding programs. Use the app to track which feeding approaches correlate with the best egg quality and hen health outcomes in your specific farm conditions.
This research focuses specifically on chicken kidney physiology and mineral handling during egg production. The findings apply to poultry farming and animal nutrition, not to human health or nutrition. Farmers should consult with poultry veterinarians or nutritionists before making significant changes to feeding programs. This study was conducted in controlled research conditions, and results may vary in different farm environments. Always follow feed manufacturer recommendations and consult with agricultural extension services for guidance specific to your flock and location.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.