What is stress?
• Any deviation from the optimum state could be
referred as stress.
• There are several factors which lead to varieties of
stress, affecting the welfare of the animals
• One of the major environmental stresses.
• Livestock face stress both during summer and winter when
environmental temperature deviates the thermo neutral zone.
• However, being endotherms, regulates the body temperature
close set point by controlling either heat production or heat loss.
• But the extreme hot or cold weather gets the animal into stress
– when the temperature exceeds the upper or lower critical temperature of
In order to reduce the
• Animal changes behavior and metabolic reactions
– quite natural on the part of animal
• But the livestock owner must follow primary managemental
– for making the micro climatic animal friendly environment
• Nutritional strategies
– However, plays secondary role to primary managemental
• When the environmental temperature goes beyond the
– Physical regulation plays in role to maintain the body
temperature of animals within in its normal range.
• When physical regulation proves insufficient, the
chemical regulation comes into play, which is important
means for combating the effects of low environmental
• A tool to measure level of heat stress
• It is a single value representing the combined effects of air
temperature and humidity associated with the level of
THI = 0.72 (W+D) +40.6
W = Wet bulb temperature oC and
D= Dry bulb temperature oC
• 70 or less -- are considered comfortable
• 75-78 -- stressful
• >78 -- extreme distress
(unable to maintain thermo regulatory mechanisms or
normal body temperatures)
• The bovine thermal comfort zone is -13ºC - +25ºC.
• Within this temperature range, the animal comfort is
optimal, with a body temperature between 38.4ºC and
Biological effects of thermal
1. Reduces feed intake accompanied by
– reduced rumination and
– nutrient absorption and
– increased maintenance requirements which results into decrease in
nutrient availability for production purposes
• Reason : Peripheral vasodilatation,
concomitantly reduced blood flow to organ systems such
as reproductive tract and GIT
2. Alters endocrine status of animal
– increase in blood concentrations of
• prolactin, ADH, aldosterone in non-ruminants, and
• catecholamines and glucocorticoids in cattle.
– Among all of them, glucocorticoids content in
blood considered to be a good index for reactions
of animals to any environmental challenges
3. Amino acid turn over gets lowered while bone resorption
which is indicated by higher alkaline phosphatase
activity (Bahga et al., 2009).
4. Reduction in growth rate in growing calves
which may be due to lower energy generation and
impaired metabolism (Bahga et al., 2009)
5. Ruminal Acidosis
(To dissipate excess heat)
Increased respiration rate Panting
Enhanced CO2 exhalation
Hyperventilation (reduced blood HCO3
- : CO2 is 20:1
Increases drooling of saliva
Reduces the quantity of saliva that
would have normally been deposited
in the rumen
Reductions in saliva entering into rumen and its HCO3
6. Nutrient requirement
• When the temperature of peripheral tissues increases more
than the rectal temperature (during thermal stress),
• The maintenance energy requirement becomes higher.
• It may increases by 7% per every oC increase in mean body
temperature (Grahm et al., 1959).
• Because of reduction of voluntary feed intake during thermal
– It is logical that mineral intake may also be reduced than the optimum
• It was noted that a 5 fold increase in K loss from skin was
measured during peak thermal stress.
• Further, the marked losses of Na, Mg, Ca and Cl, but not P are
also correlated with sweating rate.
• Thermal stress also affects the store of Vit A in
the liver and
• Increase the requirement of Vit C
– due to their increase in rate of excretion
through the urine and sweat.
Nutritional strategies to ameliorate
1. Provision of balanced feed
2. Feeding Regimen
3. Provision of clean ad libitum drinking water
4. Increasing nutrient density
5. Management of DMI
9. Feed additives 1.Buffer
3. Anti oxidants
4. Fungal culture:
Provision of balanced feed
• To compensate the reduced DMI – there is an urgent need to
increase in nutrient density
– side by side one must have to go for recalculation of mineral and water
– due to increased loss of potassium through sweat during hot and humid
environment (Collier et al., 2005).
• Cold stress proved to be less severe compared to summer
because of the consumption of large amounts of feed to
generate sufficient body heat with the utilization of feed
• Hence adoptability to cold weather well developed in moist
– provided adequate feed, and minerals and vitamin supplements are made
• Feeding behavior of most of the animals changes during
• They tend to consume more feed during cooler periods of
the day i.e. evening hours (West, 1999).
• Thus, feeding animals at more frequent intervals and
during the cooler periods of day
– Not only encourage them to maintain their normal feed intake
but will also keep feed more fresh and thus, stimulate DMI.
• In very hot weathers, more frequent feeding
– Decrease the diurnal fluctuations in metabolites and increase the
feed utilization efficiency in the rumen (Robinson 1989).
• At least 70% of the daily feed should be given fresh at night.
• Further, feeding of animals in the later part of the day could
prevent the co-occurrence of peak metabolic and
environmental heat load
Provision of clean ad libitum drinking water
• The very first step to reduce heat stress is to provision of cool
– (Especially for all lactating and dry cows plus heifers as water is the
primary nutrient needed for milk production, accounting for over 85
percent of the milk content)
• Water requirement increases significantly as the environmental
– Cows may drink up to 50% more water when the THI is >80%.
• It indicates the importance of water and its cleanliness during the
– Thus, keeping water tanks clear of feed debris and algae is a simple and
cheap strategy to help cows remain cool.
• Energy cost of
– heat of fermentation,
– work of digestion and there after the
– work of nutrient metabolism
Are the fractions which contributes to the heat increment of feeding (Webster,
• Thus, if animals suffering from heat stress is maintained on poor
quality roughages, there will be added stress of heat increment of
• Therefore, nutritionally balanced and easily digestible feeds
supplemented with protected fat and limiting amino acids may
reduce such additional stress of increased heat increment of feeding.
Management of DMI
• High fibrous diet will lead to higher proportion of acetate,
which is having more heat of nutrient metabolism as compared
to propionate (Linn, 1997).
• Thus, it appears logical that feeding low roughage and high
concentrate diet to the ruminants during summer periods to
reduces the heat production inside body.
• Pennington et al., 2004 -- Ruminant diets with grain and low
in fiber cause less heat stress for lactating cows because of
their lower heat of digestion.
• However, a minimum quantity of good quality roughage
should be fed to prevent acidosis condition
• Protein content with highly degradable materials apparently
stresses the cows further, causing an additional heat load,
– because the excess of nitrogen supplied by protein must be detoxified
to urea in liver for excretion through a metabolic pathway, which is
very high in energy demands (1g urea = 7.3 Kcal).
• The higher level of protein and degradability in the diet of
ruminants may lead to reduction in feed intake, which results
into reduced milk production (Higginbotham et al., 1989).
• Feeding Low level of less degradable protein is advisable for
encouraging the animal for DMI.
• Hence, both the quantity and form of protein in the diet are
needed to be considered when feeding heat stressed cows
• Keeping all point in view, it can be recommended that
– The level of CP in the diet should not exceed 18%
– while the level of RDP should not exceed 61% of CP
(Huber et al. 1994).
• As compared to other feeds, fats have a low heat increment
– Hence, high-fat diets have high energy conversion efficiency, could be
beneficial during hot weather
• However, research on the effects of dietary fat during hot
weather gives inconsistent results.
• Knapp and Grummer, 1991 -- Supplemental fat at 5% of diet DM
enhances lactation performance under thermo-neutral and heat
• Chan et al. 1997 -- In a study, 3% prilled fatty acids (inert)
supplementation was compared with shade plus evaporative
cooling to relieve heat stress in dairy cows.
– Results revealed that milk yield improved only by the cooling not the
fat treatment, supplementation.
• Although the results seem contradictory, but biological
principles argue in favour of fat supplementation under
conditions of heat stress.
• Nutritionists still suggest fat supplements to give a final fat
content of 6 - 7 % of diet DM, especially for high-producing
• HS associated with changes in mineral metabolism, especially
electrolytes (Na & K)
• Since these electrolytes associated with maintenance of water
balance, ion balance and the acid-base status of heat- stressed
• Need to be supplemented more than recommended levels
• Sanchez et al. 1994 –
– Na conc in the diet from the NRC recommended level of 0.18% to
0.45% or more improved milk yield by 7 - 18% &
– dietary conc of K to 1.2% or more results in a 3 - 9% increase in milk
• For heat-stressed cows, alkaline diets are more preferable
– Thus, NaHCO3 and MgO have proven very effective in alleviating to
some extent the drop in milk fat associated with heat stress conditions
(West et al. 1992).
• NaHCO3 will also increases ruminal pH, thereby establishing a
more favorable environment for fiber digestion (Santra et al., 2003).
• Escobosa et al., 1984 -- A diet with high chloride content depress the
DMI and was associated with low blood pH and reduced blood
– Researchers recommend that the level of dietary chloride should not
exceed 0.35% of DM (Sanchez et al., 1994).
• Supplementation of some trace minerals viz.,
• Chromium in its organic form i.e
– chromium yeast and chromium picolinate in poultry
– chromyl pyridine carboxylate in dairy cows
• Well-known subcutaneous vasodilator in many sp. and could
be effective for reducing body temperature.
• Unprotected niacin may be degraded in the rumen.
• Niacin helps to alleviate heat stress both by increasing
evaporative heat loss from the body and also by reducing the
effects of heat at the cell level (Lundquist, 2008).
• HS generates disequilibrium of the oxidative balance, with
important consequences over the vital function, life and death
of the affected cells
• Supplementation of antioxidants (Se, Vit E, Zn or Cu etc)
during thermal stress enhance the action of both enzymatic and
non-enzymatic antioxidants, thus nullify the undesired side
effects of free radicals
• Shivakumar et al., 2010 - Supplementation of vitamin C and
vitamin E have a negative effect on cortisol levels during heat
stress, which relieve the severity of heat stress in goats
• However, reduction in cortisol levels by vitamin E and C is not
yet fully understood
1. Choubey M and Kumar A. (2012). A nutritional
interventions to combat heat stress in dairy animal.
Vetscan. 7(1): 19-26.
2. Short course on “Nutritional and dietetics under clinic
therapeutic conditions of pet and farm animals”. IVRI,
3. Sunil Kumar B.V Kumar A and Meena K. (2011). Effect
of heat stress in tropical livestock and different strategies
for its amelioration. Journal of stress physiology &
biochemistry. 7(1): 45-54.