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Heat Stress Explained
DIETARY ELECTROLYTE BALANCE in PIGS (SWINE) (DEB)
Minerals vitally important for Pigs (Swine)
It is well known that minerals form a vital part of all biological functions
in all Pigs (Swine) species. They are more important in Pigs (Swine)
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
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 Pigs (Swine).
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 Pigs (Swine) explained
It is now possible to explain what is happening within the cells when
Pigs (Swine) 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
gives rise to the condition of alkalosis, which is a serious disturbance of
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.
Pigs (Swine) stop eating and there are various behavioral responses such as panting, increased wallowing, and muscle trembling. 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 Pigs (Swine) 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 digestive and metabolic processes is maximum. At higher environmental temperatures, the balance of electrolytes is set much higher to maintain
the same metabolic and digestive efficiency. Knowing the analytical values
of 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,
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 Pigs
(Swine) than any other nutrient. These functions include:
• Expressions and regulation of genes
• Enzyme systems within cells
• Osmotic balance
• 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 Balance
) – (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 Pigs (Swine)
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 Pigs (Swine). Heat
stress increases water consumption by at least five times the
normal level in temperate zones.
Exposure to heat stress for long periods suppresses the
responsiveness of the immune system. Increased levels of
corticosteroids in the blood reduce the activity and population
of lymphocytes in the blood.
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