Calcium and energy balance of early lactation Jersey cows, and ionized calcium stability of bovine whole blood
Calcium (Ca) was discovered in the 19th century by the chemist Sir Humphry Davy. This mineral is one of the most abundant in the world and the fifth most present element in the human body (Peacock, 2010). In the late 1900s, Sidney Ringer, a physiologist, was the first to report the importance of Ca in muscle contraction in one experiment done with frogs’ hearts. Calcium is the most important component in the body structure as approximately 99% of this mineral is found in the bones and teeth. The remaining 1% is known as total calcium (tCa), which is divided into three fractions: protein bound; ionized calcium (iCa; also known as the bioavailable part) and salts of calcium. This electrolyte plays very important physiological and biochemical functions in the body, such as: acting in cell signaling as a secondary messenger, being an enzyme co-factor, as well as, playing key roles in muscle contraction, blood coagulation, growth, gluconeogenesis, glycolysis, membrane stabilization, and cellular proliferation (Berridge et al., 1998; Jaiswal, 2001). Calcium homeostasis is regulated by three major target organs: bone resorption (e.g., Ca storage), digestive tract absorption (e.g., external source), and reabsorption in the kidneys (e.g., Ca recycling). In dairy cows, the inability of proper regulation of Ca has been associated with early lactation disease, longevity, and decreased reproductive performance causing significant economic losses. The objectives of this literature review are to afford an ample understanding of the importance of Ca, how it is physiologically regulated, how low levels of calcium can affect the lactation, and how to improve management to minimize hypocalcemia in dairy cows.