Macromineral disorders of the transition cow

Four macrominerals have the distinction of being involved in the downer cow syndrome, which is, unfortunately, often associated with parturition in cows. Inadequate blood calcium (Ca), phosphorus (P), magnesium (Mg), or potassium (K) concentrations can cause a cow to lose the ability to rise to her feet, as these minerals are necessary for nerve and muscle function. Less severe disturbances in blood concentrations of these minerals can cause reduced feed intake, poor rumen and intestine motility, poor productivity, and increased susceptibility to other metabolic and infectious disease. Extracellular fluid volume, in L, is approximately 30% of the weight (kg) of the adult animal, and is comprised of two compartments-the interstitial fluids, and plasma. Intracellular fluid volume is approximately 50% of body weight. Mechanisms for maintaining blood Ca, P, Mg, and K concentrations perform efficiently most of the time, but occasionally these homeostatic mechanisms fail and metabolic diseases such as milk fever occur. An understanding of how and why these mechanisms fail may arise from a thorough understanding of how these mechanisms work under normal circumstances and then exploring the possible sites for breakdown of homeostasis. Strategies to avoid these disorders can then be developed.