Calcium and phosphorus in broilers and layers


  • The role of calcium and phosphorus in the birds
  • Calcium and phosphorus requirements in poultry
  • Sources of calcium
  • Sources of phosphorus
  • Factors that affect the absorption of calcium and phosphorus
    • Interactions with other compounds
    • Circadian rhythm: the importance of granulometry

The role of calcium and phosphorus in the birds

Calcium and phosphorus are essential elements for the development and maintenance of the skeleton and for the eggshell formation in layers [1]–[3]. They also take part of important physiological processes such as blood coagulation or muscle contractions. Phosphorus forms other organic compounds necessary for multiple metabolic functions such as the adenosine-triphosphate molecules (ATP).

Diets that supply the proper amounts of calcium and phosphorus allows to minimize the percent of broken eggs and bone problems, as well as to optimize the organisms’ functions, which, consequently, leads to good performance results and egg quality. Due to their high calcium requirements, calcium supply is particularly important in layers.

Besides, it is important to consider calcium and phosphorus jointly, since their metabolisms are tightly related.

Calcium and phosphorus requirements in poultry

The requirements vary depending on the production stage. These variations need to be especially considered in layers because the formation of the eggshell requires high amounts of these compounds, particularly of calcium [4]. For this reason, calcium requirements increase exponentially during the pre-laying period (from 1% to 2.50%) and are even higher during the laying period (around 4%).

In broilers, the requirements of calcium and phosphorus have increased in the last decades since the major genetic lines have increased the growth rate thanks to selecting the animals for several generations. Calcium and phosphorus are necessary for bone development, particularly at early stages. When the levels of these components are below the recommended values, it is frequent to see problems related to a weak skeleton, such as femoral head break.

Sources of calcium

Calcium from mineral and animal sources are, generally, more available than the vegetal one. This is because calcium in the plants is mainly forming phytates and oxalates and it is not available for birds unless specific enzymes are included to the diets. For this reason, the supply of available calcium and available phosphorus need to be considered for each ingredient, not just the total amounts for them.

Sources of phosphorus

The main phosphorus sources are inorganic phosphates (dicalcium, monodicalcium, among others) and bone meal (not permitted in the European Union). These ingredients have a high amount of available phosphorus, compared to the phytates from plants.

Feed formulation programs use different parameters to refer to the phosphorus concentration in the diets:

  • Non phytic phosphorus: phytic phosphorus is only present in vegetal sources and is less available, as its complete digestion requires the addition of exogenous phytases to the diet (endogenous and microorganisms’ phytases do not digest this phosphorus completely). Non-phytic phosphorus is calculated form the difference between total phosphorus and phytic phosphorus.
  • Available phosphorus: it is calculated from a ingredient that is stated as a “standard”, which usually is monocalcium phosphate, who is considered to have 100% calcium availability.
  • Digestible phosphorus: obtained from in vivo evaluations, which makes it difficult to assess, though it is much more exact in terms of the quantity of phosphorus that is truly reaching the organism.

It is indispensable to know the meaning of each of these parameters and try to use the digestible values rather than the total ones as long as it is possible based on the available data for each ingredient.

Factors that affect the absorption of calcium and phosphorus

Interactions with other compounds

Calcium is mainly absorbed through an active transport system in the upper portion of the intestines. The acidification of the gut content and the presence of vitamin D and phosphorus favor its absorption. There are other factors that can affect it, for example, the excess or absence of several ions such as magnesium, manganese, or zinc, as well as other compounds such as copper and iron. All these are bivalent ions that can compete with calcium for the same absorption sites.

That is why, to supply the proper amount of calcium in the diets, the levels of phosphorus and some microminerals ought to be considered. For example, the ideal calcium to phosphorus ratio in broiler diets is 2:1, and it increases in layers during the laying period; while levels of magnesium above 1%, or below 0.2%, can cause eggshell quality problems.

Circadian rhythm: the importance of granulometry

Hens can produce a maximum of one egg per day due to the process of egg formation, which was inherited from reptiles, takes between 25 and 27 hours. The eggshell formation if the stage that requires the greatest calcium amounts and it takes plays at night.

Poultry do not eat during the night hours. For this, in layers, the particle size of calcium sources must be modified in order to supply this mineral during the night. That is why calcium requirements for layers are differentiated between rapid and slow solubility calcium.

  • Rapid solubility calcium sources are the ones presented in small particles with a diameter below 2 millimeters. The hen uses this calcium during the day for its daily metabolic functions.
  • Slow solubility calcium sources, that is, with a diameter above 2 millimeters, will stay in the gizzard and be used at night, when the gastrointestinal pH becomes more acid and facilitates calcium absorbed.

Slow solubility calcium source are important as they supply this mineral to the hens at night, when the eggshell is formed, a process that requires great calcium amounts. If a hen received rapid solubility calcium only, it will not have enough calcium in the blood for the eggshell formation and will start using the calcium stored in the bones, which will, in turn, negatively affect the skeleton and cause bone problems such as the cage fatigue syndrome.

How can Global Vet’s Lab help you?

In Global Vet’s Lab, we offer the feed formulation and analysis service to optimize feed composition and adjust it to the requirements of the species, commercial breed, ages, and productive stages. We also have a diagnostic by images service to help you find the cause of a problem observed in the farms.

To use these services, please contact us through our webpage or email at


  • [1] C. de Blas, P. Carcía-Rebollar, M. Gorrachategui, and G. G. Mateos, FEDNA (Fundación Española para el Desarrollo de la Nutrición Animal), 4th ed. Madrid, 2019.
  • [2] N. Martín, “Formación de la cáscara de huevo,” Veterinaria digital. Artículos., Jul-2019.
  • [3] Technonews, “Los requerimientos de calcio y fósforo en gallinas ponedoras,” Veterinaria Digital, 2015.
  • [4] D. Díez, “La importancia de la fisiología intestinal en la puesta de huevos,” 2020.
  • [5] Hy-Line, “Management Guide. Aviary and Barn Systems. North America Edition.” p. 21, 2016.
  • [6] H. S. Rostagno et al., Tablas Brasileñas para Aves y Cerdos. Composición de Alimentos y Requerimientos Nutricionales, 4th ed. Universidad Federal de Viçosa, Departamento de Zootecnia, 2017.

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