Chapter 4

POTASSIUM

-Third most abundant mineral in the body.

-Common plant foods good sources, however some are low.

Chemical Properties and Distribution

-Latin word for potassium is Kalium (K chemical symbol)

-Also called potash.

-Potash must be supplied as fertilizer to many soils.

-Not free in nature.

-Potassium represents 0.3% of body D.M., in skin and muscle.

-Potash present inside cells vs Na the main electrolyte in plasma and extracellular fluids.

-Blood cells 25 times as much K as plasma.

-Muscle and nerve cells 20 times K as interstitial fluid.

Metabolism

Absorption -- most small intestine (monogastrics)

-- rumen, omasum, small intestine (ruminants)

-Saliva of ruminants high in K, large amount in rumen from saliva.

-Digestibility is high (95% +) for most feeds.

-Relative K availability in corn was 90-95% and SBM 97%, compared to K acetate at 100% (Hooge and Cummings, 1995)

-Diarrhea can interfere with normal absorption.

-Potassium enters cells against a concentration gradient (active process).

-Excreted into urine as filtration and secretion.

-Fecal loss 13%, most in urine.

-12% of loss in milk.

-In sheep, 30% K excreted via skin, under hot, humid conditions.

-Adrenal hormone (aldosterone) favors reabsorption of Na and excretion of K in renal tubules.

-If insufficient aldosterone, excess K to Na.

-Hyperactivity of adrenal excess Na to K.

-Stress ↑ aldosterone, loss of K.

-Aldosterone controls K in saliva.

-In Na deficiency, Na replaced by K in saliva.

-Potassium as a free cation (+ charge) must be balanced by an anion (- charge).

-In contrast to Ca and P, K not stored and must be supplied daily.

Functions

-Maintenance of acid-base relationships, proper osmotic balance.

-Potassium in cell, Na in plasma and interstitial fluid.

-Na, K and Cl are the three major electrolytes in body, and maintain cation-anion balance.

-Na major extracellular (outside and between cells) cation (90% of total cations) in plasma and interstitial fluid).

-Potassium major intracellular (within cells) cation (75% of total).

-Active transport (energy required) regulates transport of substrates into and out of the cell.

-Intracellular-extracellular separation of Na and K handled by a Na pump.

-Need to maintain concentration gradients.

-Potassium contributes 50% of osmolality of intracellular fluid, Na and Cl contribute 80% extracellular osmolarity.

-Movement of water.

-Potassium, the principal base in regulation of acid-base balance.

-pH rigorously maintained 7.40.

-To maintain, involves respiration, blood buffering, renal excretion and reabsorption.

-Potassium important in transport of O₂ and CO₂ in blood, responsible for ½ CO₂ carrying capacity.

-Needed for nerve impulse transmission and heart beat.

-Activator or cofactor for several enzyme systems, for energy transfer and utilization, protein synthesis and CH₂O metabolism.

-Some enzymes influenced or activated, hexokinase, carbonic anhydrase, salivary amylases, pyruvic kinase, fructokinase.

-Potassium affects amino acid uptake by cells.

Requirements

-Ruminants (cattle) 0.65 - 1.3%

-Swine 0.17 - 0.30%

-Mineral highest in milk,

K - 0.15%

Ca - 0.11%

P - 0.08%

-High requirements for dairy cow, loss via milk 1.5 g/kg milk.

-For growing chicks: 0.20-0.24%

-If high energy diets: 0.30%

-Excessive amounts chlorides: 0.6-0.7%

-Significant interactions among Na, K and Cl.

-In poultry: K requirements ↑ with ↑ protein.

-Ruminant requirement: 0.5-1.0%

-Dairy cows heat stress - 1.2% k

-Stress of shipping - 1.0-1.5%

-Excitement ↑ urinary loss

-Diseases with fever or diarrhea ↑ K loss.

-Why lactating dairy cows have high requirements:

1. High milk production (high K in milk)

2. Heat stress ↑ loss through sweating and ↓ feed intake.

-Human requirements: 1.6-2.0 g/day, higher during pregnancy and lactation.

Natural Sources

-Highest in plant leaves vs seeds.

-Grains - 0.3 - 0.8%

-Vegetable proteins 1-2.5%

-Animal products -- 0.3 - 2.0%

-By-products feedstuffs (brewers dried grains, distillers dried grains, corn gluten, corn cobs and cottonseed hulls, very low (e.g., 0.04 for brewers grains).

-Alkali-treated (NH₄ or Na hydroxide) reduce K by 25% (Underwood and Suttle, 1999).

-Good sources: root crops, molasses, beet pulp, bagasse, CSM, SBM.

-Forage K affected by (McDowell and Valle, 2000);

1. Maturity

2. Species (and variety), temperate species, higher than tropical.

3. Management (crop removal)

4. Fertilization (K and N)

5. Soil and environment (e.g. weathering ↓ K)

-Potassium generally lower in regrowth forage later in season.

-Actively growing forages are 1 to 5% K.

-Deficient levels, weathered winter pasture, hay exposed to rain and sun.

-From 1-2% to 0.4-0.5 later in the season.

-In Florida, 5 of 7 ranches sampled in winter contained considerably less than 0.6% (Kiatoko et al., 1982).

-Grains inadequate for lactating dairy cows that required 0.9-1.2% K.

-Nonruminant species enough K from grains and oilseed meals.

-Variation in grains, one report corn varied from 0.11-0.54%.

History

-Sir Humphrey Davey first isolated K in 1807.

-Justis von Liebig noted importance to plants in 1840.

-Sidney Ringer found need for frog heart function with Na and Ca in 1883.

Deficiency

-For all species reduced appetite, ↓ growth, muscular weakness, stiffness, paralysis, diarrhea.

-Continued deficiency intracellular acidosis, organ degeneration, nervous disorders.

Swine

-Typical diets are adequate.

-Signs are:

↓ appetite, ↓ growth rate, rough haircoat, emaciation, inactivity, and ataxia.

Slow heart rate ↑ electrocardial intervals

No unique gross pathology.

Poultry

-Deficiency not ordinarily seen.

-Muscle weakness, weak extremities, cardiac weakness, respiratory failure.

- ↓ Feed consumption within 24 hr.

-For laying hens: ↓ egg production, ↓ egg weight, ↓ shell thickness, inability to stand.

-During stress, influence of aldosterone, K excreted.

-Heat stressed broilers + K ↑ gains (Smith and Teeter, 1987).

Ruminants

Deficiency more likely than for monogastrics.

-Milk high in K.

Why deficiency more common now:

1. ↑ use of concentrates

2. ↓ use of K-rich forages

3. ↑ use urea

Stress factors.

-Shipping stress, ↓ feedlot gains, ↓ F.I.

-Heat stress induces panting (Respiratory alkalosis).

- ↑ sweating, loss of K from sweat

-Non-specific signs:

-↓ F.I., ↓ water intake, muscular weakness, nervous disorders, stiffness, ↓ pliability of hide, emaciation, intracellular acidosis and degeneration of vital organs.

-For lactating cows, ↓ feed and water intake, ↓ milk yield, blood K ↓ in 3-5 days.

-Inanition, pica, tetany and death (Florida).

-Sheep (<0.3% K) ↓ F.I., weight loss, stiffness, death.

-In Brazil, average K of 6 grasses at 4 week 1.42% vs 0.30% at 36 wk.

Horses

-↓ growth, appetite and serum K.

-May need high K to replace K lost by sweating.

Other Animals Species

Rats -- poor growth, ↓ F.I., rough fur coat, death.

Edema ↑ "leaking" of HOH into intracellular spaces.

Dogs -- poor growth, restlessness, muscular paralysis, lesions of heart and kidney.

Rabbits - severe and rapid muscular dystrophy, diarrhea.

Humans

-Neuromuscular function (weakness to paralysis), mental confusion, soft, flabby muscles.

-Starved individuals are hypokalemic, ↓ cell mass.

-Diets high in K and low in Na favor lower blood pressure, and less cardiovascular disease.

-A transition toward modern (“westernized”) diets results in substantial decline in K intake. A large fraction of the population might have suboptimal K intake (Demigné, 2004).

-Potassium deficiency most commonly seen from severe dehydration, diarrhea, burns or other fluid losses, results of surgery.

-May occur in 20% of all hospitalized patients, and 50% of elderly.

Assessment of Status

-Low serum K (limited diagnostic value), also affected by negative N balance, G.I. losses, endocrine malfunction.

-Leakage of K from erythrocytes, false-high values.

-Acidosis ↑ plasma K "pulling it out of cells."

-Alkalosis ↓ plasma K "driving it into cells."

-Some value for ↑ serum bicarbonate ↓ chloride ↑ urine K.

-Evaluation difficult, first sign is ↓ F.I.

-Change in electrocardiogram and muscle K, limited success.

-Dietary K best indicator of status.

Supplementation

-No appreciable reserves, a daily dietary essential.

-Greatest need of ruminants receiving high concentrate diets, particularly heat stress, high milk production and transport.

-Grain - SBM for swine and poultry for 16% protein contains 0.75% K.

-K is 90-97% available.

May need if:

1. Alternative protein source.

2. Perhaps newly purchased pigs during 2-wk receiving diet.

3. Heat-stressed broilers.

-Likelihood of K deficiency for ruminants as high-forage diets replaced with low K containing grains, by-products (e.g., CSH, corncobs) and urea.

-Corn silage is lower in K than other forages.

-Low K in mature pastures, that have weathered, overly mature, exposed to rain and sun.

-OK if provided molasses (4.0% K) in winter.

Mature tropical forages are low, but likewise low in energy, protein, P, Na, Ca, and a number of trace minerals.

-176% ↑ in K lost in sweat from cow at 30 C vs 20 C.

-Potassium loss from skin 5 times greater for unshaded cows (Malloneé et al., 1985).

-High producing cow secretes 25 to 40% daily intake.

-Acute K deficiency (stress or disease) from diarrhea.

-Stressed animals ↑ adrenal hormones (conserve Na, excrete K).

-Feedlot cattle need 1.3% K, first two weeks to prevent death.

-Human diets, typically no problem (meat, fruits and leafy vegetables).

-Diets decreased in Na and increased in K lower blood pressure (Nowson et al., 2004).

-To obtain enough dietary K, human should consume “5-10” servings of fruits and vegetables (Demigné, 2004).

Potassium salts provided:

1. Potassium lost from G.I. fluids, vomiting and diarrhea

2. ↑ K in urine from diuretics

3. ↓ K in plasma caused by electrolyte shifts (e.g., treatment of diabetic acidosis).

4. Cardiac dysfunction

-Supplemental forms of K are unpalatable, need to combine with palatable ingredients.

-Chemical forms, chloride, carbonate, bicarbonate and orthophosphate equal in bioavailability (~ approaching 100%).

Toxicity

-Maximum dietary tolerable level for livestock species is 3%.

-Signs of toxicosis, cardiac insufficiency, edema, muscle weakness and death.

-Others feel 3.0% is incorrect, grazing ruminants consume immature forages that often contain 4-5% K.

-Also ingested K beyond requirement is quickly excreted.

-Aldosterone may often be more important to the grazing ruminant by controlling K excess vs conservation of Na (Michell, 1995).

-Excess K is most important as an influence on milk fever and hypomagnesium tetany.

-Milk fever -- K is the major source of excess bases (cations), a problem when dietary anions are low. Excess cations affect vitamin D receptors, result Ca not withdrawn from bones.

-An increase of dietary K from 1.1% to 2.1% in prepartum diets ↑ milk fever (old Jersey cows) from 10 to 50% (Goff and Horst, 1997).

-Reducing dietary K in prepartum diet most effective step to reduce milk fever last 3 weeks of pregnancy. Cows require low or negative DCAD.

-Hypomagnesemia - K has two effects (Dua and Care, 1995):

1. High soil K ↓ Mg concentration in grass.

2. High dietary K ↓ Mg available by reducing Mg absorption from rumen.

-Mg absorption by sheep ↓ if diet contains more than 3.0% K (Phillips et al, 2005).

-High K (4-5%) doubles the Mg requirement.