• Oct 10, 2026

Eggshell quality and trace minerals: what layer feed needs to get right

Why shell quality matters more now

On 6 October 2026, Saudi Arabia's Ministry of Environment, Water and Agriculture (MEWA) reported egg production of more than 9 billion eggs in 2026, and self-sufficiency of 100% in table eggs [1]. With the home market now supplied by local flocks, every egg lost to a poor shell is a loss the local industry carries itself.

Those losses are not small. One study cites about 10–15% of eggs lost to eggshell quality problems before or during collection [2]. Cracked eggs are a food safety issue as well as a financial one, because bacteria can get in through the shell [3]. Shell problems also become more common as hens age [3].

Shell quality depends on genetics, health, housing and handling as well as feed. This article covers the feed side: calcium, vitamin D3 and three trace minerals.

How a shell is built

A shell is about 95% calcium carbonate [4]. The hen puts about 2 g of calcium into each shell. The diet supplies 60–70% of that, and the rest comes from a reserve in the bones called medullary bone [4].

Timing matters. Shell formation takes about 20 hours and happens mainly at night, when the hen is not eating [4]. So the question is not only how much calcium is in the feed, but whether it is still available in the gut during the night.

The shell also has an organic framework, and three trace minerals help build it [2]:

• Zinc is part of carbonic anhydrase, the enzyme that produces bicarbonate, the raw material for the shell's calcium carbonate [2][5].
• Manganese activates glycosyltransferase, which helps form the crystal nucleation sites and controls how calcite crystals grow [2].
• Copper is part of lysyl oxidase, which forms cross-links in the shell membranes. Copper deficiency can lead to abnormal membranes [2].

Calcium: particle size matters

The 1994 NRC requirement for white-egg layers eating 100 g of feed a day is 3.25% calcium, or 3.25 g per hen per day. A footnote adds that the requirement may be higher for maximum shell thickness [6].

Particle size is where many feeds differ. A meta-analysis of 71 experiments published between 1971 and 2019 found that coarse limestone stays longer in the gizzard and is dissolved more completely there than fine limestone [4]. Going from 0.15 mm to 1.5 mm particles increased shell thickness by 1.1% and shell breaking strength by 3%, with no effect on production performance [4]. The authors explain this by coarse particles releasing calcium through the night, when the shell is being formed [4].

"Coarse" in this work means particles larger than 0.8 mm. There is no consensus on the best coarse-to-fine ratio, though 75% coarse and 25% fine is often used for older hens [4]. The response to coarse limestone was greater when dietary calcium was below the optimum [4].

Vitamin D3

Vitamin D is needed to absorb calcium and phosphorus [7]. When hens are fed a diet short of vitamin D, the first sign is thinner eggshells [7]. In the body it is converted to an active form that stimulates calcium absorption in the gut. As hens age, levels of that active form fall and calcium absorption declines [4].

NRC lists 300 IU of vitamin D3 per kg of diet at 100 g of feed a day [6]. A metabolite, 25-hydroxyvitamin D3, is also used commercially. Whether it gives better results than vitamin D3 is still debated [7].

Trace minerals: manganese, zinc and copper

NRC 1994 lists 20 mg/kg manganese and 35 mg/kg zinc at 100 g of feed a day. It gives no copper figure for laying hens; the table shows a question mark [6]. These are 1994 estimates for Leghorn-type hens, not commercial specifications.

Two trials show why the levels used in practice matter:

• Older hens. A corn-soybean diet already contained about 33 mg/kg zinc, 25 mg/kg manganese and 5 mg/kg copper. Adding zinc, manganese and copper improved shell breaking strength and fracture toughness in hens aged 60 and 69 weeks. The effect was the same whether the minerals came from organic or inorganic sources [8].
• Cutting levels. In late-lay hens, reducing inorganic trace minerals to a third of the commercial level lowered shell strength and increased egg losses over an eight-week trial [2].

Heat adds pressure

Hot climates make this harder. Panting in heat-stressed birds upsets the acid-base balance of the blood and leads to respiratory alkalosis, and heat stress lowers egg quality [5]. For Gulf layer flocks, the summer months are when shell specifications matter most.

What a mill buyer can check

Item	What to ask for	Why
Limestone	Particle-size distribution (sieve analysis) for each lot, including the share above 0.8 mm, plus calcium content	Particle size affects how much calcium is available overnight [4]
Layer feed by phase	The coarse-to-fine limestone ratio used for older flocks	Older hens absorb calcium less well [4]
Vitamin D3	Declared and analysed vitamin D3 in the premix, plus expiry date	Deficiency first shows as thinner shells [7]
Trace minerals	Analysed manganese, zinc and copper in the premix compared with the label, and total levels in the finished feed	The base diet already contributes some, as the trial above shows [8]
Records	Batch numbers and a certificate of analysis for each delivery	SFDA requires batch-level records of incoming materials [9]

When shell quality drops, these records let you rule the feed in or out quickly, before looking at health, housing or handling.

If you would like to talk through layer feed specifications, contact BioSpec.

References

1. Ministry of Environment, Water and Agriculture (MEWA). MEWA adopts 5 qualitative initiatives to support poultry industry localization. 6 October 2026. https://www.mewa.gov.sa/en/MediaCenter/News/Pages/mewa-5-initiatives-poultry-localization.aspx (also Saudi Press Agency, https://www.spa.gov.sa/en/N2694658)
2. Qiu JL, Zhou Q, Zhu JM, Lu XT, et al. Organic trace minerals improve eggshell quality by improving the eggshell ultrastructure of laying hens during the late laying period. Poultry Science 2020; 99(3): 1483–1490. https://doi.org/10.1016/j.psj.2019.11.006
3. Cheng X, Ning Z. Research progress on bird eggshell quality defects: a review. Poultry Science 2023; 102(1): 102283. https://doi.org/10.1016/j.psj.2022.102283
4. Hervo F, Narcy A, Nys Y, Létourneau-Montminy M-P. Effect of limestone particle size on performance, eggshell quality, bone strength, and in vitro/in vivo solubility in laying hens: a meta-analysis approach. Poultry Science 2022; 101(4): 101686. https://doi.org/10.1016/j.psj.2021.101686
5. Wasti S, Sah N, Mishra B. Impact of heat stress on poultry health and performances, and potential mitigation strategies. Animals 2020; 10(8): 1266. https://doi.org/10.3390/ani10081266
6. National Research Council. Nutrient Requirements of Poultry, 9th revised edition. National Academy Press, 1994, Table 2-4 (nutrient requirements of Leghorn-type laying hens). https://doi.org/10.17226/2114
7. Adhikari R, White D, House JD, Kim WK. Effects of additional dosage of vitamin D3, vitamin D2, and 25-hydroxyvitamin D3 on calcium and phosphorus utilization, egg quality and bone mineralization in laying hens. Poultry Science 2020; 99(1): 364–373. https://doi.org/10.3382/ps/pez502
8. Mabe I, Rapp C, Bain MM, Nys Y. Supplementation of a corn-soybean meal diet with manganese, copper, and zinc from organic or inorganic sources improves eggshell quality in aged laying hens. Poultry Science 2003; 82(12): 1903–1913. https://doi.org/10.1093/ps/82.12.1903
9. Saudi Food and Drug Authority. Technical Requirements for Feed Factories and Warehouses. 2025. https://www.sfda.gov.sa/sites/default/files/2025-04/TechnicalRequirementsFeedFactoriesWarehouses_0.pdf