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Heat Stress Explained
DIETARY ELECTROLYTE BALANCE in POULTRY (DEB)
Minerals vitally important for Poultry
It is well known that minerals form a vital part of all biological functions
in all Poultry species. They are more important in Poultry nutrition than
any other nutrient, being involved in the
expression and regulation of genes, in enzyme systems regulating cellular functions, osmotic balance, detoxification systems, and acid-base balance and structurally in bone metabolism.
To properly understand the importance of minerals it is necessary to take a trip back through time, to millions of years ago when life evolved from water to dry land.
For survival, a barrier (skin) evolved between the surrounding air and the fluid environment within cells. Systems had to develop to regulate the fluids within and surrounding the cells. Water was required to transport nutrients, gasses, waste products and hormones around the bodies.
Water also plays a critical role in lubricating and in balancing acids and alkali (bases) and other products of metabolism. It also has a great capacity to dissipate heat produced by reactions such as occur in digestion and during heat stress.
This is achieved electrically in conducting solutions that are produced when electrolytes are added to water. For instance, in the fluid between cells there are the key electrolytes, sodium bicarbonate (NaHCO
) and chloride (Cl) and within the cells potassium (K), phosphate (P), magnesium (Mg), some sodium (Na), calcium (Ca) and bicarbonate
) are found.
It is fascinating to find that the electrolytic activities of water are maximised at 37°C i.e., the approximate body temperature of poultry.
As they are present in very small quantities, the concentration of
electrolytes is expressed as milliequivalents (mEq). This is a measure
of electrical charge and the potential to generate acids or bases. A major
function of electrolytes is to assist in the maintenance of water balance
within the body.
The regulation of water balance in the body is under control of hormones
such as A.D.H. [Anti-Diuretic Hormone]. For instance, if the concentration
of electrolytes in the blood plasma falls, A.D.H. release is suppressed and
urine flows freely. The converse applies, as A.D.H. release increases the
flow of urine will decrease.
Thirst is the driving force of water balance.
The key electrolytes Sodium (Na), Potassium (K), Chloride (Cl), Bicarbonate
have different essential functions.
Cell function in Poultry explained
It is now possible to explain what is happening within the cells when Poultry
are outside their
Zone of Comfort
. There is some tolerance and adaptation to temperatures as high as 25°C but above this, Heat Stress is evident.
Open mouth breathing and panting are designed to cool the deep body
temperature by evaporating water from the surfaces of the lungs and
respiratory tract. Water evaporation requires a considerable amount of heat
energy, thus temperature is reduced. The body loses carbon dioxide [ CO
and in the process bicarbonate [HCO
]. The progressive loss of CO
ise to the condition of alkalosis, which is a serious disturbance of acid-base
Loss of electrolyte balance is perhaps the most serious outcome. All the body systems are affected when Dietary Electrolyte Balance (DEB) is lost. The major effect of this is the development of a complex alienation of the body chemistry following a rise in the deep body temperature. Normal heat regulating systems are soon overcome, hyperventilation (panting) occurs in an effort to cool the body by evaporating water from the lungs. In continuing hot and humid conditions this fails, there are severe changes in the blood, acid base balance (which is essential for normal functioning) is lost and so is the productivity of enzyme systems within cells.
Poultry stop eating and there are various behavioral responses such as squatting and wing spreading. Lost electrolyte balance results in the loss of potassium, sodium and bicarbonate in an increasing urine output.
The signs that the farmer sees in his Poultry are the result of an attempt to
reduce the deep body temperature by losing heat. In the process, a succession
of electrolyte changes occurs. Panting increases the evaporation of water from
the surface of the lungs by a factor of 4+. It produces a higher concentration of potassium [K
] in the urine and a lower concentration of bicarbonate [HCO
in the blood. A demand for bicarbonate is induced. The end products of
metabolism within the cells are usually acids, which means there is an increase
in hydrogen ions [H
] these are neutralised by bicarbonate [HCO
Zone of Comfort
(temperature and humidity) there is a balance of
electrolytes (measured in milliequivalents) at which the efficiency of the
and metabolic processes is maximum. At higher environmental
the balance of electrolytes is set much higher to maintain
the same metabolic
and digestive efficiency. Knowing the analytical values
the feed components
is important. The DEB is calculated by the formula
) – (CI
Higher temperatures demand higher values
In order to raise overall dietary electrolyte balance to values demanded by
higher temperatures and relative humidity, the demand for bicarbonate,
sodium and potassium must be met. For maximum productivity to be achieved,
salt (sodium chloride) should not be added to these diets because of the strong
negative effect of chlorine.
In summary then
Minerals are a more integral part of all biological functions in Poultry than
any other nutrient. These functions include:
Expressions and regulation of genes
Enzyme systems within cells
Acid-Base Balance and
Structural tissue e.g. bone
Sodium, Potassium, Chlorine, Sulphur and
Bicarbonate form ions. According to their electrical
charge ions are either Cations (+) (positive) or
Anions (-) (negative).
This equation articulates the importance of Dietary Cation Anion
Balance (DCAB) more popularly known as Dietary Electrolyte
) – (CI
Managing the balance of dietary electrolytes is a key factor in
maximising performance in production-limiting environments.
The manipulation of DEB must be carefully controlled.
3. Acid-Base Balance in Poultry
Maintenance of acid-base equilibrium is fundamental to life. Enzyme
systems, metabolic functions and performance measures depend on this equilibrium. The pH of blood is maintained in the range 7.3 – 7.5 by
buffer systems based essentially on HCO
(bicarbonate ion). Panting
respiration is an important reaction in the effort to cool the body by
evaporative cooling through loss of water from lungs. This results in
metabolic alkalosis due to rapid loss of CO
. Thirst is increased, more
urine is excreted and with it key electrolytes. Constant replacement
of Sodium, Potassium and Bicarbonate is required.
Increasing DEB values of the by supplementation of Sodium and
Potassium improves average daily weight gain of chickens.
Water is the most important nutrient for Poultry. Heat stress increases
water consumption by at least five times the normal level in temperate
Exposure to heat stress for long periods suppresses the responsiveness
of the immune system. Increased levels of corticosteroids in the blood
the activity and population of lymphocytes in the blood.
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