Dietary electrolyte balance in chickens

Dietary electrolyte balance in heat stressed broiler chickens

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High ambient temperatures coupled with high humidity can be devastating to commercial broilers. Heat stress interferes with the broiler´s comfort and suppresses productive efficiency. Although increased heat is seen as a major problem in poultry production, studies show that it is not only the excessively high temperatures, but also the fluctuation of the temperature which is more detrimental for a broiler to perform. Heat stress is a significant source of economic loss for the broiler producers worldwide. Increased mortality and depressed feed intake and retarded growth rate associated with heat stress have been well-documented.

As ambient temperature increases, birds start to pant to get rid of the heat load by evaporation. Evaporative heat loss through panting is the most important mechanism to control body temperature under heat stress. However, panting is accompanied with increases in respiratory rates. The increased respiratory rate causes higher losses of CO2 and results in increased blood pH and disruption of acid-base balance (Toyomizu et al., 2005). When this balance is altered towards alkalosis or acidosis, metabolic pathways are diverted to homeostatic regulation rather than used for supporting growth. Moreover, under heat stress, birds lose more water (through panting and urine) than they do when they are in the thermal comfort zone. A decrease in body water results in a reduced ability to dissipate heat via evaporation and through increased peripheral blood flow. As a consequence, birds increase water consumption to compensate for water loss and to increase the heat dissipation capacity. However, water retention is reduced due to the increased electrolyte excretion in urine and feces (Belay et al., 1992; Belay and Teeter, 1996). Reductions in intracellular water adds further stress to the bird and understanding how this can be minimized will facilitate identification of effective dietary and management treatments.


Electrolytes are chemical substances that separate, when dissolved in fluids, into electrically charged particles (ions) capable of conducting electric currents vital for the function of nerves and muscles.

The major cations (positively charged electrolytes) in the body´s fluid are sodium, potassium, calcium, and magnesium. The major anions (negatively charged electrolytes) are chloride, phosphate, sulfate, and bicarbonate. Organic acids such as lactate, pyruvate, and aceto-acetate also carry negative ions.

Calcium is the most abundant electrolyte in the body. About 99 percent of calcium is stored in the teeth and bones where it helps to make and keep them strong. Moreover, calcium is also critical for muscle contraction, nerve signaling, blood clotting and maintaining normal heart function. Normal serum calcium values range from 8.5 to 10.2 mg/dL.

Sodium is the major extracellular cation. It regulates the total amount of water in the body and plays a major role in neuronal and nerve signaling. Normal serum sodium values range from 135 to 145 mEq/L. Potassium is the major intracellular cation.

Potassium is essential for the proper functioning of the heart, kidneys, muscles, nerves, and digestive system. The normal blood potassium level is 3.5 to 5.0 mEq/L.

Phosphate makes up one percent of a person´s total body weight. A majority of the body´s phosphate is found in the bones and teeth where it promotes their formation. It also plays an important role in the body´s utilization of carbohydrates and fats. Phosphates are also critical to the synthesis of proteins that promote the growth, maintenance, and repair of cells and tissues. Normal values range from 2.4 to 4.1 mg/dL.

Chloride is the major extracellular anion found outside the cell. Chloride plays a critical role in keeping the proper balance of body fluids and maintaining the body´s acid-base balance. The normal chloride values are 96 to 106 mEq/L.

Magnesium is the fourth most abundant mineral in the body. Half of the body´s magnesium is found in the bone and the other half is found mainly with in the cells of body tissues and organs. Magnesium is needed for more than 300 biochemical reactions in the body. It helps maintain normal muscle and nerve function, keeps the heart rhythm steady, supports a healthy immune system, and keeps bones strong. Magnesium also helps regulate blood sugar levels, promotes normal blood pressure, and is also involved in energy metabolism. Normal serum values of magnesium are 1.7 to 2.2 mg/dL.

General functions of electrolytes

  1. Maintenance of fluid balance by adjusting the volume of water intake, mainly by drinking more or less fluid.
  2. Promotion of neuromuscular function by helping in transmission of nerve impulse, establishing resting membrane potential, action potentials in nervous and muscle tissue.
  3. Regulation of acid-base balance by maintaining the blood pH in a range of 7.35-7.45.
  4. Facilitation of enzyme reactions by taking part in biochemical reactions in the body.

Acid-Base Balance

The body has three lines of defense to regulate the body´s acid-base balance and maintain the blood pH around 7.4 viz.

  1. Blood buffers
  2. Respiratory mechanism
  3. Renal mechanism

Blood buffers

A buffer may be defined as a solution of weak acid (HA) and its salts (BA) with a strong base. The buffer resists the change in pH by the addition of acid or alkali and the buffering capacity is dependent on the absolute concentration of the salt and the acid. Buffer cannot remove H+ ions from the body rather it acts as a temporary shock absorbent to reduce the free H+ ions. The H+ ions have to be ultimately eliminated by the renal mechanism. The blood contains 3 buffer systems viz.

  1. Bicarbonate buffer consisting of sodium bicarbonate and carbonic acid. It is the most predominant buffer system of the extracellular fluid, particularly the plasma.
  2. Phosphate buffer consisting of sodium di-hydrogen phosphate and di-sodium hydrogen phosphate. It is mostly an intracellular buffer and is of less importance in plasma due to its low concentration.
  3. Protein buffer consisting of the plasma protein and hemoglobin together.

Respiratory mechanism controlling electrolyte balance

This is achieved by regulating the concentration of carbonic acid in the blood. i.e the denominator in the bicarbonate buffer system. The large volumes of CO2 produced by the cellular metabolic activity endanger the acid-base equilibrium of the body. But in normal circumstances, all of this CO2 is eliminated from the body in the expired air via the lungs.

The rate of respiration (or the rate of removal of CO2) is controlled by a respiratory centre, located in the medulla of the brain. This centre is highly sensitive to changes in the pH of blood. Any decrease in blood pH causes hyperventilation to blow off the CO2, thereby reducing the H2CO3 concentration. Simultaneously, the H+ ions are eliminated as H2O.

Renal mechanism for pH regulation

This involves

  1. Excretion of H+ ions
  2. Reabsorption of bicarbonate
  3. Excretion of titratable acid
  4. Excretion of ammonium ions.

Excretion of H+ ions: H+ excretion occurs in the proximal convoluted tubules (renal tubular cells) and is coupled with the regeneration of HCO3- (Fig 1).

Fig 1. Renal regulation of blood pH-Excretion of H+ ions (CA- Carbonic anhydrase)

Reabsorption of bicarbonate: This mechanism is primarily responsible to conserve the blood HCO3-, with a simultaneous excretion of H+ ions. The normal urine is almost free from HCO3- (Fig 2).

Fig 2. Renal regulation of blood pH- Reabsorption of bicarbonate (CA – Carbonic anhydrase)

Excretion of titratable acid: Titratable acidity is a measure of acid excreted into urine by the kidneys. Titratable acidity reflects the H+ ions excreted into urine which resulted in a fall of pH from 7.4 (that of blood). The excreted H+ ions are actually buffered in the urine by phosphate buffer as depicted in Fig 3.

Fig 3. Excretion of titrable acid

Excretion of ammonium ions: This is another mechanism to buffer the H+ ions secreted into the tubular fluid. The H+ ion combines with NH3 to form ammonium ion (NH4+). The renal tubular cells de-aminate glutamine to glutamate and NH3 is produced. This reaction is catalyzed by the enzyme glutaminase. The NH3, liberated in this reaction diffuses into the tubular lumen where it combines with H+ to form NH4+. Ammonium ions cannot diffuse back into tubular cells and, therefore, are excreted into urine. This is explained in Fig 4.

Fig 4. Renal regulation of blood pH- Excretion of ammonium ions (CA- Carbonic anhydrase)

Sodium-potassium pump

The pump, with bound ATP, binds 3 intracellular Na+ ions. ATP is hydrolyzed, leading to phosphorylation of the pump at a highly conserved aspartate residue and subsequent release of ADP. A conformational change in the pump exposes the Na+ ions to the outside. The phosphorylated form of the pump has a low affinity for sodium ions, so they are released. The pump binds 2 extracellular K+ ions, leading to the dephosphorylation of the pump.ATP binds, and the pump reorients to release potassium ions inside the cell so the pump is ready to go again. As the plasma membrane is far less permeable to sodium than it is to potassium ions, an electric potential (negative intracellularly) is the eventual result.The electrical and concentration gradient established by the sodium-potassium ATPase supports not only the cell resting potential but the action potentials of nerves and muscles. Export of sodium from the cell provides the driving force for several facilitated transporters, which import glucose, amino acids and other nutrients into the cell. Translocation of sodium from one side of an epithelium to the other side creates an osmotic gradient that drives the absorption of water. Another important task of the Na+-K+ pump is to provide a Na+ gradient that is used by certain carrier processes. In the gut, for example, sodium is transported out of the resorbing cell on the blood side via the Na+-K+ pump, whereas, on the resorbing side, the Na+-Glucose symporter uses the created Na+ gradient as a source of energy to import both Na+ and Glucose, which is far more efficient than simple diffusion. Similar processes are located in the renal tubular system.

Heat stress in broiler and dietary electrolyte balance

Heat stress occurs when heat accumulation from metabolism and the environment exceeds the ability of the bird to lose heat. In response, the bird increases its respiration rate ("panting") so as to increase evaporative cooling from the respiratory tract. This panting can result in the development of respiratory alkalosis and a reduction in blood bicarbonate (HCO3–) concentrations. In addition to elevated blood pH, plasma electrolyte concentrations are altered. Attempts to limit the adverse effects of heat stress through nutritional means have included the manipulation of the mineral content of feed and water. The objectives have been to increase water intake and, therefore, improve the efficiency of heat dissipation from the respiratory tract, and to increase the intake of certain minerals to restore plasma electrolyte concentrations to normal levels. Heat stress also depletes K+ and other minerals in the body, altering the delicate electrolyte balance in the body.

The electrolyte balance in birds is altered during heat stress due to panting. By adding electrolytes to the feed or water, birds increase their water intake, which aids in keeping a constant body temperature and maintains an effective system of evaporative cooling. DEB of 250mEq has been shown to be required for optimal productive metabolism in chickens (Mongin, 1981; Borges et al., 2003). The value of dietary electrolyte balance (DEB), defined as the concentrations of [(Na+) + (K+) – (Cl–)] in mEq/kg, as a practical predictor of growth in poultry is unresolved. Mongin (1981) indicated that growth is optimized when the DEB is 250 mEq/kg but the usefulness of the equation for predicting the growth of birds, especially during heat stress, is questionable (Gorman and Balnave, 1994). A number of factors should be considered.

  1. The DEB equation assumes the only minerals that have an important impact on acid-base balance are Na+, K+, and Cl–, with no consideration given to the form in which they are ingested. There is considerable evidence that metabolizable anions exert an influence on acid-base balance. Gorman and Balnave (1994) found carbonate salts to yield poor growth at 30°C regardless of DEB. Weight gains associated with sodium carbonate (Na2CO3) and NaHCO3 were significantly different despite the diets having identical DEB. They concluded that heat stress may induce a metabolic requirement for the bicarbonate ions.
  2. The DEB equation does not take into consideration other specific ion effects and this limits the usefulness of the equation (Gorman and Balnave, 1994). Also, divalent cations are not as readily absorbed as monovalent cations (Mongin, 1981). Replacement of NaCl or KCl with CaCl2 results in an increase in the amount of HCO3– exchanged for a given amount of Cl– in the intestine. Therefore, during heat stress, the physiological state of a bird already deficient in HCO3– could worsen. 

DEB formulation and level of inclusion

An example of DEB calculation based on total levels of monovalent minerals in a theoretical broiler prestarter feed using salts (to give 0.25% total Cl) and sodium bicarbonate (0.3%) is given here:

Sodium (Na) 0.28% x 434.98 factor = 121.79 mEq/kg

Potassium (K) 0.75% x 255.74 factor = 191.80mEq/kg

Chloride (Cl) 0.25% x -282.06 factor = -70.51 mEq/kg

DEB = 243.08 mEq/kg

Murakami et al. (1997) reported that Na+ requirement of broiler was no more than 0.20% up to d21 and not more than 0.15% on 42-56 day of age. They also reported that Cl- level higher than 0.20% was of no benefit. Rondon et al. (2001) reported that the Na+ and Cl- requirements for optimum performance of young broiler chickens were 0.28% and 0.25% respectively. Borges et al. (2003a) found that in thermo- neutral room DEB 240mEq increased 42d weight gain & 44d lymphocyte % and DEB 240mEq treatment significantly increased 0-21d wt. gain compared to DEB 40,140 and 340 mEq. Borges et al. (2003b) reported that under moderately high ambient temperature blood HCO3 and pH increased with DEB 360mEq/kg causing respiratory alkalosis but DEB of 240mEq/kg gave best wt gain and FCR. Olanrewaju et al. (2007) used 174mEq & 241mEq DEB and 8IU of ACTH in saline/kgBW & same vol. of saline were injected per day for 7d on d35. Birds fed 241mEq exhibit significantly higher Na+ and Ca2+ levels than the other on d35. They also reported that infusion of ACTH significantly increased hematocrit, Hb, pCO2, corticosterone, osmolality and HCO3-. Reduced pH, body weight, pO2 and plasma Na+ and Cl- in both diets compared with control group at 42 and 49 d of age. Babiker et al. (2009) conducted experiment on IBD vaccinated birds with diets having only basal diet and basal diet supplemented with electrolytes and vitamins. Reduced mortality from 40-24% and increased bursa to body wt, lower pathological change of bursal tissue and mean antibodies titre elevation were observed in diet supplemented with electrolytes and vitamins. Adekunmisi and Robbins (2009) reported that for a diets containing 14.3%, 21.4% and 28.6% CP the optimum DEB were approx. 250 mEq, 325 mEq and 400 mEq/kg and they concluded that the optimum dietary electrolyte balance of broiler chicks is dependent on diet crude protein content. Raymond and Hector (2012) reported an optimum electrolyte balance from 250-300mEq/kg and high dietary Ca reduced plasma inorganic P levels.

Table 1. Convenient factors, and their derivation, for calculating dietary electrolyte balance (DEB) based on the total levels of macro-minerals in diet


The most important factor affecting performance in broilers subjected to high temperature is reduced feed intake. High temperature accompanied by high humidity is more detrimental to broiler performance than high temperature with low humidity. Nutritional manipulation such as the addition of fat and reduction of excess protein are recommended. During hot periods, lower protein diets supplemented with limiting amino acids give better results than high protein diets. Maintenance of both CO2 and blood pH is critical to heat-stressed broilers and the addition of ammonium chloride and potassium chloride to the drinking water to maintain this balance is advised.

Full list of reference is available on request 

April 10, 2013

Very interesting and very clear article about heat stress!

The dietary electrolyte balance can be easily influenced by choice of raw materials. Of course this choice can be limited in some regions or even due to purchase positions. In that case, a solution is to add an additive to the feed. Sodium formate added at 3 kg/ton, improves dEB with about 45 mEq/ton of feed. Together with the 45 mEq improvement you have the benefits of formate with it as well: in a broiler trial in very hot summer conditions and high humidity a huge decrease of mortality was seen in the broiler group which received sodium formate, compared to a negative and a positive control. Also there was an improvement seen in FCR and droppings.

This trial was carried out in Spain with Imasde.

Khaled Ahmed Khaled Ahmed
Specialist in Animal Nutrition
April 11, 2013

I disagree with Dr. dipanjal Kakoti
Betaine can be obtained naturally or synthetically, Natural betaine is extracted from sugar beet molasses by using chromatographic separation processes, whereby complex mixtures can be divided and separated to individual components based on their chemical and/or physical characteristics. While, synthetic betaine is produced as the result of a reaction between, Trimethylamine (TMA) and monochloracetic acid (MCA) or Betaine and hydrochloric acid (HCl) or TMA, MCA, ethylene oxide and HCl from chloroacetic acid, sodium hydroxide and trimethylamine. It is usually sold as the hydrochloride salt, (betaine HCl).
When Synthetic betaine included, it adds both betaine and chloride to the final feed. High chloride content – can disrupt cellular water balance and interfere with betaine’s key osmolytic function, leading to wet litter and poorer performance. Also, TMA residues can lead to undesirable ‘fishy eggs’ in layers, particularly in strains of hen deficient in trimethylamine oxidase.

Sudipto Haldar Sudipto Haldar
Animal Nutritionist
April 11, 2013

Absolutely correct comment about synthetic betaine. In fact sometimes synthetic betaine may cause more harm if the chloride content is too high. Not only that, if betaine with high chloride content is kept mixed with premixes then it may cause severe damage to the premix. The main constraint towards usage of natural betaine is the price - probably. However, if synthetic betaine with low chloride content is available then it may be highly efficient in alleviating heat stress.

Dr.asim Khan Dr.asim Khan
Veterinary Doctor
April 11, 2013

I think along with minerals and vit especially vit C, addition of glucose in drinking water is also a good remmedy in heat stress. This will give extra energy because all of us know panting in broilers lower down the FCR.

April 12, 2013

As per natural betaine is concerned its nice to see the inputs of Mr. Khaled, but my concern is to the field condition. Where availability round the year and affordability is the question.

To study this question, an in vitro trial was setup to mimic gastric passage. The University of Ghent evaluated the biological equivalence of different betaine sources (monohydrate and anhydrous produced by extraction vs. betaine hydrochloride and anhydrous, produced by chemical synthesis), using Mass Spectromety combined with HPLC analysis in a model that simulates gastric passage.

Results showed that irrespective of the ionic form and production method (natural extraction vs. chemical synthesis) different sources of betaine gave the same analytical results. As after gastric passage both molecules proved to be identical, no differences in biological activity or osmoregulatory function between betaine hydrochloride and betaine anhydrous as an effective feed additive could reasonably be expected.

Sudipto Haldar Sudipto Haldar
Animal Nutritionist
April 12, 2013

To Dr Asim - What about using sodium bi carbonate in summer stress?

Leo Antony Leo Antony
Consultant in Poultry management and training
April 13, 2013

Surely, there are any number of vitamins, minerals, probiotics and other formulations listed here and elsewhere that can help in relieving heat stress in chicken. More suggestions, especially those based on technical expertise as well as experience will definitely be welcome and helpful. While I agree that these are of immense help, people should not be led away by the false belief that these alone will work wonders in solving the problem of heat stress. I say this because many flock managers look at these as substitutes for what other practical and correct measures can and should be taken in the poultry sheds. I believe that a good understanding of the dynamics of heat stress along with right husbandry practices are the basic essentials of summer management. For example, flock managers should know how to identify the probable deep body temperatures of their birds by looking at the progressive patterns of behaviour of their birds in their response to rising heat because finally it is the deep body temperature that decides on the results- STRESS, RECOVERY or DEATH from heat stress.They should also know what the lethal effects of the different levels of deep body temperatures are when they persist in birds for different stretches of time during the day. Many managers are also not aware of the reasons as to why birds die in large numbers after sunset when the shed temperatures drop considerably. I have also noticed other serious management errors like using the fogging system inside the sheds when the temperatures go very high -without providing fans. In such cases, they are not aware that they are raising the humidity to unhealthy levels without reducing the temperature sufficiently. The resulting situation is often counter productive and even disastrous. Only when these basics are in place, one can surely draw benefits from the several effective chemical therapies that have been suggested in this forum and elsewhere.

???? ??????? ???? ???????
Doctor of Veterinary Medicine
April 15, 2013

Dear friends
I want to know the amount of vitamin C by kgms that I can add to one ton of feed and what is the temperature that I need to start adding vitamins.

Kamal Kamal
April 16, 2013

Chromium tripicolinate -yield good benefits in stress related conditions in broilers.

April 19, 2013

Sodium sulphate has a good scope in the near future. It is an adequate replacement for sodium chloride as synthetic betaine has negative effects of chloride (as mentioned by Dr. Haldar). Also, it replaces sodium bicarbonate adequately (sod sulphate is required almost 16% less than soda bicarb to balance the same sodium). Dietry bicarbonate binds to H+ ions released in the gut from the blood (besides bicarbonate released in the gut from the blood in lieu of chloride absorbed), thus forming water and CO2. No bicarbonate goes directly into the blood. In contrast, the Sulphate from sodium sulphate is non-absorbable and is excreted, thus does not causing any acidity. Thus, Sulphate quenches ammonia in the excreta and litter forming ammonium sulphate (an inert compound), thereby reducing litter ammonia drastically.

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