Heat Stress Home
Heat Stress Explained
Dietary Electrolyte Balance
in Dairy Cattle
DEB (DCAB) - Dietary Electrolyte - Dietary Cation - Anion Balance
DNA testing (mitrochondrial) confirms that the "Humped Cattle of India" [Bos indicus] and the "Humpless Cattle of Europe" [Bos taurus] evolved from the original Wild Aurochs (now extinct) - some hundreds of thousands of years ago.
Zone of comfort
5°C - 20°C (41°F - 68°F)
15°C - 25°C (59°F - 77°F)
16°C - 27°C (61°F - 80.6°F)
Heat shock proteins
Responses to hostile conditions i.e. higher Temperatures than
Zone of Comfort
and greater than 50% Relative Humidity (See
) are largely dependent
on the concentration of Heat Shock Proteins. These are protective
molecules produced by special genes dating back to the early stages of
is the hereditary material.
Cross-bred cattle (indicus x taurus) will therefore be intermediate in their
response to hostile conditions.
Cattle make crucial adjustments
C noticeable adjustments are made by both breeds of cattle, Bos
taurus responding more actively.
The response of cattle to hot/wet and hot/dry conditions is twofold:
Towards the reduction of metabolic heat and
Towards the utilisation of all mechanisms to promote the
loss of heat.
• Appetite is depressed and water consumption increases
• Maximum heat loss is by evaporation of water from the
lungs and skin. Respiration rate increases and may develop
into panting or even gasping.
• Activities are shifted to early morning or early evening.
Experimentation has shown that exposure to 40
C for 7-10 hours will induce
severe panting, gasping and drooling, sweating and drastically increased water consumption.
Relative Humidity increases the problem
When the relative humidity exceeds 50%, the dissipation of heat by evaporative cooling becomes much more difficult and signs of heat stress develop sooner.
Any deviation from optimal (Zone of Comfort) conditions results in physiological behavioural stress adaptation which is made at
the expense of production -
decreased live weight gains and reduced feed
conversion efficiency are the
Cells adapt to protect from heat damage
As this stress adaptation develops, diversionary activity within cells and in
their membranes escalates, to protect their structures and productive
machinery from heat damage. Cellular metabolism is disturbed, membranes
close down some of their operations altogether. Energy is almost exclusively
diverted to preventing a rise in the deep body temperature.
Acid base balance
As a result of these physiological responses there are changes in acid-base balance, there is loss of homeostasis and the frank loss of key electrolytes (Sodium, Potassium and Bicarbonate).
If the severity of the stress progresses, lethargy, lassitude, weakness,
stupor, staggers and death may result.
illustrates the sequence of changes and their
outcomes and the most appropriate methods of control and treatment.
Details of the biochemistry of Heat Stress in Cattle and of the importance of
dietary electrolyte balance in the nutrition of cattle under hostile conditions
are to be found
©Ruth Consolidated Industries Pty Ltd ©Rural Chemical Industries (Aust) Pty Ltd. All Rights Reserved