Calcium: physiological role, sources and doses in diets of commercial poultry (review)

Calcium is extremely important in the nutrition of farm animals and poultry, so a search is underway for optimal calcium-containing ingredients with high bioavailability and low cost. The physiological effects of calcium extend to all organs and systems (G.S. Baird, 2011). In the body, 99 % of calcium are bones, and 1 % is accumulated in soft tissues (D. Oberlis et al., 2008). Nowadays, fundamental and clinical research proves that the role of calcium in physiological processes is not limited to the formation of bone structure and eggshells. The secretion and action of hormones, the permeability of cell membranes, nerve conduction, and muscle contractions depend on blood calcium concentration (R. Stehle et al., 2007; E.T. Kavalali, 2015). Calcium increases collagen synthesis, which accelerates wound healing (J. Zhang et al., 2021). Calcium ions as cofactors, affect the functions of proteins (C. Umerah et al., 2023). Apoptosis and its intensity, as well as the intercellular adhesion in connective tissue formation are calcium-dependent (D. Goll et al., 2003). The bone mass in the body is genetically programmed. If there is a lack of calcium during the growth period, the body will not reach the required parameters (K. Okuyama et al., 2022). It is logical that one of the most important pathognomonic causes of a wide range of pathologies may be calcium deficiency, impaired absorption, and low bioavailability. Generally recognized sources of calcium are its salts, e.g., carbonate, citrate, lactate, dicalcium phosphate, gluconate, sulfate and their combinations with vitamin D3, trace elements, estrogens (F. Zhang et al., 2018; B.L. Damron et al., 1995; N.S. Strelkov et al., 2008; L.P. Yang et al., 2018). The significant difference between these forms is their bioavailability. The mechanism of calcium availability from salts is known and depends on several factors, primarily the dose, the simultaneous levels of synergists and antagonists, the acidity of gastric juice, and the mode of consumption (F. Bronner, 2023; S. Christakos, 2012; R. Alexander et al., 2023). Therefore, it is necessary to carefully select the diet composition with regard to multiple interactions between its components in the gastrointestinal tract. The review covers the issues of calcium metabolism in animals and birds, the approved dietary calcium levels in Russia and abroad, the mechanisms of calcium absorption in the gastrointestinal tract, synergistic and antagonistic interactions of calcium ions with other elements, organic compounds, and metabolic pathways of calcium transformation in various body systems.