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Metabolic functions of
potassium in animals and Dietary potassium requirements for poultry

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  1. 1. POTASSIUM Editor: Dr. John Summers Two articles appeared recently in the Feedstuffs magazine, "Metabolic functions of potassium in animals explored" (August 28, 1995) and "Dietary potassium requirements for poultry explored" (September 4, 1995). Both of these articles were produced by D.M. Hooge and K.R. Cummings. Since acid-base balance is receiving more attention with respect to certain metabolic problems encountered with poultry, it was felt that the following summary of these articles may be of interest. Importance and Body Disposition Potassium is an extremely important mineral in the body, being the third most abundant after calcium and phosphorus. It has an extremely important function along with sodium and chloride in maintaining optimum acid-base balance in the body. The body contains approximately .3%K, as compared to .15% Na and .15% Cl. Primary organ sites for K are muscle 56%, skin 11% and bone 10%. K is located almost exclusively in the cells with only around 3% located extracellularly. Importance in Acid-Base Balance In contrast to Na, the main electrolyte in blood plasma and extracellular fluid, K is present in every cell in the body. To maintain acid-base balance in blood, Na is countered primarily by Cl ions and to a lesser extent by bicarbonate cans (HC03). The cell K, and the small quantity of Na present, are off-set primarily by phosphoric acid and to a lesser extent by sulphate and chloride. Potassium Deficiency Symptoms Potassium deficiency symptoms are mainly metabolic and can include neuromuscular and cardiovascular problems. Such conditions reported are:  reduced release of insulin from the pancreas, resulting in glucose intolerance  depressed appetite  intracellular acidosis  increased cardiac output  reduced renal filtration rate, thus increased loss of sodium and potassium  skeletal weakness leading to stiffness and paralysis  necrosis disorders Because K is a water soluble and a very mobile element, it must be supplied in the diet daily. As mentioned previously a deficiency can result in reduced feed intake.
  2. 2. Primary Functions One of the main functions of K is to maintain osmotic pressure and water balance.  functions in neutralizing acids  important in transport of oxygen and carbon dioxide in blood  acts as a co-factor in several enzyme systems involving energy transfer and protein synthesis Muscular activity results in the exchange of Na and K across cell membranes. As much as 30% of cellular K can be lost by continuous exercise or physical activity. The heart beat, a continuous and very essential muscular activity, requires a proper balance of K and Ca for proper rhythmic activity. Potassium Requiring Enzymes As demonstrated by Mongin (1981), there is an optimum acid-base balance that must be maintained in the body for various enzyme systems to function normally. Enzymes have specific pH requirements and any deviation from these, results in a loss in efficiency. K acts with other ions such as Na, Ca and Mg in maintaining proper electrolyte balance. Metabolic Acidosis Intracellular acidosis occurs when an animal becomes depleted of K, due to disease, stress or low dietary K intake. Since there are no appreciable reserves of K in the body, depletion can readily occur. In K depletion Na enters the cell, along with H+ions; thus causing an increase in acidity within the cell. This electrolyte imbalance, and shift in pH, disrupts the cell's metabolism. If the condition is not corrected by an intake of K, function of vital organs could be impaired. Active Transport Cell membranes are not as permeable to Na as they are to K and Cl. Therefore mechanisms exist, referred to as sodium pumps, which move Na out of cells against electrical and chemical gradients. Amino Acid Transport K is known to influence the uptake of amino acids into cells and plays an active role in protein synthesis. The requirements of lysine and arginine for optimum growth, depends on the electrolyte balance of the diet. Potassium Loss via the Kidneys
  3. 3. Reabsorption of Na in the kidneys takes place with urinary excretion of K, in order to maintain blood osmotic pressure and electrolyte balance. Excess K in the blood is readily excreted in the urine and this leads to increased urine output with diets high in K. Animals can become depleted of K in stressful situations such as disease or during transport, as the animal has a limited ability to conserve K even when it is deficient in the body. Potassium Toxicity Since K is readily excreted by the animal in the urine, excessive intakes can usually be readily handled. However, large intakes can be toxic if not balanced with similar intakes of Na. Heat Stress It has been shown that chickens markedly increase their K excretion, in relation to other minerals, during heat stress. Thus ammonium chloride, (NH4)Cl, plus sodium bicarbonate (Na HC03) in the feed have been shown to be beneficial in maintaining acid-base balance and alleviating heat stress problems. Potassium for Poultry While potassium levels are generally reviewed in poultry feed formulation, they are seldom given maximum or minimum limits. Part of the reason for this is that K requirements are not well defined and also there is considerable variation in feed ingredient levels. As mentioned previously, much has been written about the importance of Na, K and Cl in maintaining proper acid-base balance in the body, in order for animals to perform at an optimum level. However, the ideal balance between these electrolytes has not been well defined for poultry. Estimated Requirements There has been a lot of work done looking at the response to dietary supplements of Na, K and Cl. In many cases these studies have been done with purified or semi-purified diets with birds housed in cages and thus little or no disease or environmental stress. Even under such conditions, the results obtained have been extremely variable and probably of limited value to those formulating diets for commercial poultry operations. From the work reported with practical broiler diets, with a level of approximately .25% Cl, the Na:K ratio, to maintain an optimum milli equivalent ratio, would be a dietary level of .75% K with Na ranging from .22 to .79%.
  4. 4. Future Needs In the past, research has attempted to find optimum dietary levels of the various electrolytes, with only minimum attention paid to diet acid-base balance. Marked dietary electrolyte balance changes do occur in ration formulation, with various ingredient combinations, and the use of more synthetic amino acids at the expense of intact protein sources. Recent work has demonstrated that K levels in the body can be significantly reduced by stress, high environmental temperatures, and an excessive intake of other electrolytes. Hence, more work is required to investigate the role of K in some of the metabolic diseases such as ascites, malabsorption syndrome, spiking mortality and leg problems. These appear to have become more of a problem in recent years, at a time when diet electrolyte balance has been changing. Reference: Mongin P., 1981. Recent advances in dietary anioncation balance. Applications in poultry Proc. Nutr. Soc. 40:285-298.