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Organic minerals improve eggshell strength and keel bones in chickens

December 15, 2023
 Cage free egg production trends and impact on the welfare of laying hens

Cage-free egg production: trends and impact on the welfare of laying hens

Cage-free systems have been the most impactful trend for egg producers in recent decades. Also called “alternative” systems, they already account for over 60% of eggs produced in the European Union (Graph 1), and the European Commission is currently assessing the feasibility of banning cage systems starting in 2027. The share of cage-free hens has also been steadily increasing in the United States: it currently stands at 39%, more than twice what it was in 2018 (18%). A recent survey has revealed that major U.S. egg producers believe that 66% of the nation’s hens will be cage-free in 2030. Likewise, on a worldwide level, many large egg producers, retailers, food service companies and hotel chains have committed to banning cage systems from their egg supply chains.

Graph 1: Share of laying hens housed in each system (enriched cage, barn, free-range or organic), European Union. Source: European Commission.


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Cage-free houses provide laying hens with more space and equipment (litter, slats, nests, etc.), which enables greater mobility and increased expression of the birds’ natural behaviors. However, even cage-free farming can be associated with some welfare concerns, such as wet litter, air quality, gut health, several parasitic and infectious diseases, feather pecking and keel bone fractures, which need to be addressed by egg producers.

Keel bone fractures

Keel bone fractures (Image 1) are an important welfare problem of modern egg production. Cage-free housing systems have been associated with a significantly higher prevalence and severity of keel bone fractures (KBF), and most researchers believe that KBF are due to trauma from collisions with house equipment. However, a recent study reported that collisions cannot be responsible for most fractures, proposing instead that KBF develop from the inside of the keel by a mechanism not yet understood.

Image 1: Keel bone fractures, from normal (left) to most severe (right).
Source: Wilkins et al., (2011).


Total Replacement Technology™ (TRT): impact on egg quality, mineral excretion and bone health

Animal feed has traditionally been supplemented with high levels of inorganic trace minerals (ITMs). Those ITMs undergo antagonistic reactions with important feed components, such as other minerals, vitamins, antioxidants and enzymes, thereby reducing the nutritive value of feed. Furthermore, the use of high levels of ITMs generates a heavy load of minerals in the manure. In order to reduce mineral excretion and mitigate the associated environmental impacts, it is necessary to decrease the level of mineral supplementation, without sacrificing the health and performance of farm animals.

Genetic companies have made remarkable progress in the selection of laying hens with improved persistency in lay and eggshell quality. Production standards are now available until 100 weeks of age, and hens may produce over 500 eggs. However, in many countries, laying hen flocks are still routinely depleted around 80 weeks of age, due to non-genetic factors that affect flock performance and egg quality. Among those factors, eggshell defects are the main reason to terminate a layer flock.

An effective solution to optimize egg production and eggshell quality with a reduction in mineral excretion can be achieved by replacing ITMs with organically bound minerals at lower inclusion levels. Qiu et al. (2020) accomplished a significant reduction in the fecal concentration of Zn (-44%), Mn (-53%), Cu (-58%) and Fe (-61%) when ITMs were totally replaced with much lower levels of organic trace Zn, Mn, Cu and Fe (just one third of the supplemented ITM levels). The same study also showed a significant reduction in the percentage of rejected eggs (soft shells, broken shells, misshapen eggs and other defects).

Image 2: Total Replacement Technology (TRT)

More recently, a study was performed in brown laying hens, over five cage-free farms, to investigate the effect of replacing ITMs with organic trace minerals (OTMs) on eggshell strength, mineral excretion, keel bone and tibia traits*.

The control and treatment birds received diets of the same specifications, except for Zn, Cu, Mn, Fe and Se. Control birds received a diet supplemented with ITM only, at conventional levels. The treatment group’s diet was supplemented with OTM only, using Total Replacement Technology™ (TRT): ITMs were totally replaced with organic trace minerals for Zn, Cu, Mn and Fe, at approximately 40% of ITM levels used in the control diet, and the inorganic Se source was replaced with organic selenium yeast.

Despite the reduced mineral supplementation in the diet, eggshell strength was significantly improved in treatment (TRT) birds during the trial (p˂0.05), whereas the mineral content in the feces of Zn, Mn, Cu, Ca, K and Na was significantly lower (p˂0.05, Table 1). These results further validate that TRT™ significantly reduces mineral excretion in the feces of laying hens, due to the higher bioavailability of organic trace minerals. The reduced excretion of Ca, K and Na is likely a consequence of the reduced antagonistic interaction when removing ITMs from the diet, allowing for improved intestinal absorption.

Table 1: Mineral content in the manure


Tibia breaking strength, Ca and P contents were unaffected by treatment (Graph 2). Calcium and phosphorus percentages in keel bone ash were greater in TRT birds, while ash percentage and keel bone breaking strength were lower (p˂0.05, Graph 3). However, TRT birds had a lower keel bone damage score than the control in the caudal (p˂0.05, Table 2), middle and cranial portions of the keel, which means that TRT had a lower percentage of birds with damaged keels (fractures and/or deviations).

Graph 2: Tibia chemical and mechanical traits

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Table 2: Keel bone damage scores


Graph 3: Keel bone chemical and mechanical traits

Lower keel bone damage score in TRT birds was associated with reduced mineralization. The healing process of KBF goes along the formation of a fracture callus, in which a greater mineral content is found. A higher number of fractures results in more callus formation, which can explain this study’s results.

The finding that keel bone damage was greater in the group with greater keel breaking strength indicates that other bone structural factors, still unidentified, have a role in the development of keel bone damage. This is in agreement with recent research on KBF (Thøfner et al., 2020).

These novel findings demonstrate that TRT can increase eggshell strength and reduce mineral excretion, while maintaining tibia strength and alleviating keel bone damage in laying hens.


*Presented at the XIXth European Symposium on the Quality of Eggs and Egg Products, Kraków (Poland), September 2023 (Estevinho, J., Walker, H., Taylor-Pickard, J. Total Replacement Technology™ (TRT) improves eggshell strength and keel bone health, while reducing mineral excretion.

References are available upon request: