Today, poultry farmers, let’s talk about a painful subject—eggshell quality.
When eggshell quality declines, egg traders lower their prices, breakage rates soar, the eggs look less appealing, and they become harder to sell. After working hard to raise the flock for more than half a year, who wouldn’t be upset to see profits take a major hit because of eggshell problems?
But the problem is that when many farmers notice eggshell quality declining, their first reaction is, “Just add some calcium and it’ll be fine.” Poorer eggshell quality is often the result of several factors acting together. If you don’t identify the real “culprit,” simply adding calcium may not solve the problem at its root.
In this article, I’ll break down the 5 main reasons eggshell quality deteriorates to help you pinpoint the problem and address it appropriately.
I. Nutritional Imbalance: The “Prime Suspect” in Poor Eggshell Quality
Eggshells are composed of approximately 95% calcium carbonate, so the importance of calcium needs no further explanation. But many poultry farmers don’t realize that the problem often lies in the “way calcium is supplied,” not just in the “amount of calcium added.”
More than 90% of eggshell formation takes place at night. The calcification process in the uterine section of a laying hen’s oviduct takes about 20 hours to complete. This means there must be a continuous, sufficient supply of calcium ions in the blood at night. If the calcium in your feed is mainly in the form of fine powder, it is absorbed quickly during the day, leaving no calcium supply at night.
The right approach is to combine coarse and fine particles: coarse calcium particles (2－4mm) should account for 60％－70％ and release calcium slowly at night; fine calcium particles should account for 30％－40％ to meet the need for rapid absorption during the day. The calcium-to-phosphorus ratio also matters; the ideal ratio is 5：1￣6：1. When total phosphorus exceeds 0.45％, it can actually inhibit calcium absorption.
Another easily overlooked “hidden killer” is vitamin D？. Vitamin D？ promotes active intestinal calcium absorption; when deficient, calcium cannot be used effectively even if the diet contains sufficient calcium. Research indicates that when serum 25－（OH）－D？ concentration is below 30 ng／mL, the incidence of sand-shell eggs rises by more than 37％. The latest research from the Chinese Academy of Agricultural Sciences also found that flavonoids can increase eggshell breaking strength by 4.18％－15.02％, while manganese at 120mg／kg can increase breaking strength by about 15％. The biological efficacy of organic manganese is 115％－406％ that of inorganic manganese.
II. Stress and lighting: the “hidden killers” ignored by most people
Many farmers have no problem with their nutritional formulas, but their eggshell quality still does not improve. At this point, you should investigate stress factors.
Sudden noises, strangers entering the chicken coop, water or power outages, and climate change can all cause endocrine disorders in laying hens, disrupting the secretory function of the shell gland. Heat stress is especially significant: in high temperatures, chickens dissipate heat by panting, which raises blood pH and inhibits carbonic anhydrase activity. Carbonic anhydrase is a key catalyst required for calcium carbonate synthesis. Data show that under prolonged high temperatures in summer, the incidence of sandpaper-shelled eggs is 2－3 times higher than in winter.
Lighting management is equally important. During the laying period, daily lighting duration should remain stable at 16 hours, with an intensity of no less than 10.76 lux/m²; it should not be increased or decreased arbitrarily. Continuous lighting suppresses melatonin secretion and disrupts calcium metabolism, leading to reduced eggshell quality and accelerated reproductive aging. In addition, studies have shown that switching to red LED lighting for the final 2 hours of the lighting period can increase the expression of calcium transport proteins in the shell gland and improve eggshell thickness.
III. Disease factors: the “ticking time bomb” that directly destroys the oviduct
If eggshell problems suddenly worsen and are accompanied by a sharp drop in the laying rate, disease should be treated as a serious possibility.
Newcastle disease, infectious bronchitis, egg drop syndrome, and other viral diseases can directly damage the oviduct, leading to thinner and paler eggshells and an increase in shell-less eggs. Among these, atypical Newcastle disease is more common in actual production; its symptoms are not typical, but it continuously damages eggshell quality.
Bacterial salpingitis is also a major cause of declining eggshell quality. In laying hens with salpingitis, the expression of calcium transport proteins and eggshell matrix proteins in the oviduct is suppressed, directly resulting in thinner eggshells and reduced strength. Salpingitis occurs most often during peak egg production and is characterized by the absence of a production peak, poor eggshell quality, and declining egg quality.
The key to disease prevention and control is to ensure vaccination, regularly monitor antibody levels, maintain hygiene in the poultry house, and arrange laboratory diagnosis promptly when abnormalities are detected.
IV. Increasing Hen Age: An “Inevitable Natural Process” That Cannot Be Reversed but Can Be Delayed
No matter how hard you try, eggshell quality declines as laying hens enter the late laying period—this is an objective fact. The problem is that many farmers do not know that the “critical turning point” for the decline in eggshell quality occurs at 50－55 weeks of age.
The specific data are as follows: eggshell strength peaks at 50 weeks of age at 51.26N, then drops to 43.78N by 72 weeks of age; eggshell thickness decreases from 0.36mm to 0.33mm; and the effective layer ratio decreases from 79.61％ to 75.04％.
Why does this happen? The latest research from the Chinese Academy of Agricultural Sciences found that an imbalance in the gut microbiota is an important factor in the decline in eggshell quality in older laying hens. As laying hens enter the older age stage, the balance of the gut microbiota is disrupted, impairing intestinal calcium transport and ultimately leading to a decline in eggshell quality. At the same time, uterine redox imbalance, metabolic reprogramming, and changes in the structure of the uterine microbiota lead to reduced pigment synthesis and transport capacity, making eggshell color lighter.
This means that slowing the decline in eggshell quality must start with gut health; simply adding calcium is far from enough.
V. Mycotoxins: “chronic poison” hidden in feed
Finally, let’s discuss a problem that many livestock farmers tend to overlook—mycotoxins.
Zearalenone and ochratoxin A can damage liver function, affect the activation of vitamin D, and interfere with estrogen secretion, leading to delayed development or abnormal function of the oviduct. Studies show that when the zearalenone content in feed exceeds 100μg／kg, the proportion of eggs with sandpaper-like shells can increase significantly.
This threshold is actually easy to exceed. Especially during hot, humid seasons, if feed ingredients are stored improperly, excessive mycotoxin levels are almost inevitable.
Summary: When eggshell quality deteriorates, don’t rush to “supplement calcium”—first identify the right direction
A quick recap of the five main causes of deteriorating eggshell quality:
① Nutritional imbalance—an imbalanced calcium-to-phosphorus ratio, insufficient vitamin D?, and an unsuitable calcium source particle size
② Stress and lighting—heat stress, unstable lighting, and sudden environmental changes
③ Disease factors—Newcastle disease, infectious bronchitis, egg drop syndrome, and salpingitis
④ Increasing flock age—eggshell quality naturally declines after 50 weeks of age; gut microbiota are key
⑤ Mycotoxins—damage the liver and endocrine system, indirectly affecting eggshell quality
Eggshell quality problems result from a combination of factors. If you notice a decline in eggshell quality, it is recommended that you investigate in the following order: first, check the feed formulation (calcium-to-phosphorus ratio, vitamin D?, proportion of coarse-particle calcium) → then check environmental management (lighting duration, temperature, stressors) → next, investigate disease (with particular attention to oviduct health) → finally, consider the flock’s age in weeks and gut health status.
Only by identifying the problem and intervening precisely can eggshell quality truly be improved. Good eggshells mean good egg prices, ensuring better farming returns.
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