




































                               American International Journal of Multidisciplinary Scientific Research; Vol. 1, No. 3; 2018 

ISSN 2638-1249  E-ISSN 2638-1273 

Impact Factor: 5.8 

Published by Centre for Research on Islamic Banking & Finance and Business 

 

 

4 
 

Optimizing Animal Productivity under Heat Stress Conditions 

Using Conventional and Recent Technologies 
 

 

Alsaied Alnaimy Mostafa Habeeb
1 

  

1
Biological Applications Department, Radioisotopes Applications Division, Nuclear Research Center, Egyptian 

Atomic Energy Authority, Inshas, Cairo, Egypt. 

  

Correspondence: Prof. Dr. Alsaied Alnaimy Mostafa Habeeb, Biological Applications Department, Radioisotopes 

Applications Division, Nuclear Research Center, Egyptian Atomic Energy Authority, Inshas, Cairo, Egypt. Email: 

dr_alnaimy@yahoo.com, Tel: 00201283912177 

 

 

Received: September 12, 2018           Accepted: September 30, 2018   Online Published: October 2, 2018   

 

 

Abstract 

When the animals exposed to the high environmental temperature most of the physiological and biochemical 

parameters are disturbances. The heat-induced changes in each of thermoregulatory parameters as well as water, 

protein turnover or balances and hormonal levels may be used for evaluation the animal's adaptability to hot climate. 

Detection of such phenomena in the animals could be achieved by different indices. Most of indices which may be 

used for detecting the heat adaptability in animals are reviewed in this article paper. 

 

Keywords: Animal Productivity, Heat Stress Conditions, Conventional and Recent Technologies. 

 

INTRODUCTION 

Heat is the major constraint on animal's productivity in sub-tropical arid zone regions. Growth, milk production and 

reproductive performance in both male and female animals are impaired as a result of the drastic changes in 

biological functions caused by heat stress (Habeeb et al., 1989, 1992, 1993 and 1997). The average milk yield and 

growth of the European cattle are adversely affected reaching in some cases, one-half when transferred to tropical 

and subtropical countries (Kamal, 1982 Kamal, et al., 1989 and Marai and Habeeb, 1998). The most adaptable 

animals to such conditions are those which manifest the least deviations in their traits when introduced to such 

conditions. However, there are individual differences in these changes between breeds and within bread. The 

difference in the response of such animals under hot climatic conditions is due to their difference in heat adaptability 

measured by heat tolerance which is the ability of the animal to express its inherited production potential during its 

life-time when raised under the hot conditions (Kamal, 1982). The heat tolerance indices may be used for selection 

the heat tolerance animals within or between breeds. Heat adaptability indices for predicting the productive animals 

under hot conditions are based on production level, water balance, protein balance, thermal response and heat 

induced changes in hormonal levels (Habeeb, et al., 2007 and 2008). 

In tropical and subtropical countries, animal breeders raising European breeds select the animals which 

maintain high body weight gain or high fertility under hot climate. However, using the production level 

as an indication of adaptability is a rather time-consuming, since it takes 15-16 months to measure the 

mature body weight and 30 months or more to estimate the fertility and milk efficiency of doe. Besides, 

culling of such expensive animals because of their failure to hold their high level of production is a big 

loss of money. Moreover, body weight gain of heat stressed animals is a misleading index of heat 

adaptability, since it may be due to the increase in water retention and not to the increase in body protein and 



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fat (Kamal and Johnson, 1971). In other words, a unit of body weight gain in one animal may be due to the increase 

in body water at the expense of body tissue loss, while in the other, may be due to the increase in body solids. 

Therefore, it is erroneous to consider the first animal as adapted to heat as the second animal, though both had 

similar apparent body weight gain. It is concluded that using the production level in estimating the heat adaptability 

in farm animals is impracticable but using some techniques in estimating the heat tolerance in farm animals is easily, 

quickly and more available as shown in this article paper. 

Providing with suitable housing, feeding, disease and parasite control and heat stress alleviation practices, together 

with amelioration of the environment, can help heat stressed animals to express their genetic potentials in tropical 

and sub-tropical areas. This is in addition to carrying out properly routines managerial practices at the suitable times. 

Alleviation of heat stressed animals can be applied by physical, physiological and nutritional techniques. In tropical 

and sub-tropical countries, climatic heat is the major constraint on animal productivity. Growth, milk production and 

reproduction arc impaired as a result to the drastic changes in biological functions caused by heat stress (Habeeb et 

al., 1992 and Marai et al., 1995 & 1997). The decreases in growth and milk yield of the European cattle may reach 

one-half when introduced to tropical or sub-tropical environment (Habeeb et al., 2000& 2008 &2009). Generally, 

good management should aim to well-being, comfort and maintaining high productive and reproductive efficiency 

of the animals. Under hot climate conditions, the major objective is to facilitate overcoming heat stress, although 

such criteria is sometimes difficult because its occasional high costs, altogether with that most countries in which it 

occurs have severe financial constraints. The managemental practices concerned in hot climate, which will be the 

subject of the present article involve modification of the environment, reducing the animal's heat production and 

increasing its heat loss. 

Buffalo's reaction to hot climate 

The heat stressful conditions induce a vast array of biological changes including disturbances in protein, energy and 

mineral metabolism, which depress (with about 50%) productivity of temperate breeds introduced to a tropical or 

sub-tropical environment (Kamal 1975; Habeeb, et al., 1992 and Marai, et al., 1995).To overcome such unfavorable 

conditions, it is needed to ameliorate such environment and select more adaptable livestock.  

Selection of desirable stock of hot climates should be for animals physiologically equipped to withstand heat and 

drought. This could be achieved by selection according to the morphological characteristics that could assist to adapt 

to hot climate and/or according to the actual ability to maintain expression of the inherited potentials that is estimated 

by change in either thermal, water or nitrogen balance, after testing the animals under hot climatic conditions.  

Among the climatic components that may impose stress on animals are temperature, humidity, air movement and 

radiation, of which the temperature is the most important. In tropical and subtropical conditions, animals are faced 

with many problems that relate to hot climate, particularly heat stress, poor quality postures, diseases and parasites, of 

which heat stress is the most important. In such conditions, animals are exposed to direct and indirect solar 

radiation (estimated by about 4200 Kj/h /square meter of body surface, in Egypt), increase in metabolic heat 

production and difficulty in heat loss. 

The disturbance in protein metabolism occurred as a result of the depression in appetite and consequently less feed 

intake as well as the decrease secretion of anabolic hormones, especially thyroxin under hyperthermal conditions, 

may be responsible for the decrease in blood serum proteins in buffalo calves under SHS and HS. The depression in 

protein biosynthesis in heat stressed calves may also lead to the pronounced increases in concentrations of the end 

products of proteins catabolism, i.e. serum urea-N and creatinine (Habeeb et al., 1992). 

a. Physiological and biochemical changes: 

Under hot climate conditions, normal thermoregulatory reactions, i.e. respiration, sweating and rectal temperature are 

increased causing disturbances in the metabolism of water (increase water intake and body water content), protein, 

energy and minerals (negative nitrogen, energy and mineral balances). These disturbances also occur in enzymatic 

reactions e.g. an increase in transaminase enzymes activities and in hormonal secretion where insulin, T4, T3 and 

aldosterone decrease and cortisol increases. Such disturbances lead to depression in some of the blood metabolites, i.e. 

glucose, total protein, total lipids, cholesterol, etc. The final result of these changes is impairment of appetite, feed 

intake, feed efficiency, food utilization, growth milk yield and reproduction (Habeeb et al., 1992). 

Among the most important non-genetic factors affecting both quantity and quality of milk in dairy animals are lactation 

number, season of calving and stage of lactation. These factors may alter the animal responses to high environmental heat. 

Milk hormones depend mainly on a continuous supply of hormones from the blood to the mammary glands. This transportation 

of the hormones may be affected by exposure of animals to high ambient temperature. Most of pituitary, thyroid and adrenal 

hormones in both plasma and milk were affected by heat exposure (Habeeb et al., 1992). Habeeb et al (2000) studied the 

effect of lactation number and ambient temperature on T3 and cortisol levels in milk and blood and milk composition of 

lactating Water buffaloes.  The data showed that milk yield and T3 either in milk or in blood besides milk fat, protein 

and lactose were significantly lower in July (37.1°C) than in February (17.5°C) while the opposite trend was noted 



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for cortisol levels either in milk or in blood. The same authors showed that averages of weekly milk yield in buffaloes 

exposed to 37.1°C during July month were significantly lower than those obtained from buffaloes exposed to 17.5°C during 

February month in all lactation numbers. From the overall mean of the 6 lactations, it was found that exposure of 

animals to high environmental temperature caused a depression in milk yield by 16.6%. 

Habeeb et al (2000) found that T3 concentrations in both plasma and milk and their ratio in buffalo were 

significantly affected due to increase of ambient temperature from 17.5° to37.1°C. The overall mean of the 6 

lactations showed that plasma T3 decreased by 17.2%. However, this change was inconstant in all lactations. In the 

6th and the 1st lactations which characterized by the lowest milk yield, the percentages of decline were highest and 

reached 20.9 and 22.5%, respectively. While at the 3rd and the 4th lactations which were characterized by the 

highest milk yield, the plasma T3 was not affected due to increase of ambient temperature.   

Habeeb et al (2000) found that plasma T3 values either under 17.5 or 37.1°C was higher at the 1st lactation and 

exhibited a marked reduction with increasing milk yield until the 4th lactation followed by a rapid increase reaching 

the highest values in the 6th lactation. It seemed that distribution curves of plasma T3 as affected by lactation 

number had an opposite trend of milk yield curves. A negative correlation between T3 level in blood and milk yield 

was found in buffaloes. The decline in plasma T3 in the 3rd and the 4th lactation number may be due to higher 

utilization of plasma T3 which supply the accelerated process of milk synthesis. Milk T3 concentration declined 

significantly due to exposure of animals to high ambient temperature in hot summer as compared to mild winter 

season. The lowest values were in the milk of the 4th or the 3rd lactation and the highest values were in the milk of 

the 6th and the 1st lactations. These changes through 6 lactations, in general, were comparable to the alterations of 

plasma T3 (Habeeb et al., 2000). The authors reported that the decline in T3 content in secreted milk as a result of 

increasing ambient temperature could be related to a reduction in the same hormone content in plasma. Plasma 

T3/milk T3 ratio decreased significantly due to increase of ambient temperature. This indicates that the decline in 

plasma T3 was more than in milk T3. In addition, T3 was higher in plasma (5- 6 times) than in milk at all 

temperature conditions and at all lactation numbers (Habeeb et al., 2000). 

Habeeb et al (2000) found that cortisol hormone levels increased significantly either in' plasma or in milk in all 

lactation number due to increase in ambient temperature from 17.5°C to 37.1°C. The overall mean of plasma cortisol 

values of the 6 lactations were 9.07 and 12.53 ng/ml during February and July, respectively. The corresponding 

values for milk cortisol were 1.53 and 2.51 ng/ml. The percentage of increase in cortisol due to heat exposure was 

higher in milk (64%) than in plasma (38%). Therefore, plasma/milk ratio decreased significantly as ambient 

temperature increased. The same authors added that plasma cortisol varied in parallel to the changes in milk yield 

along the 6 lactation numbers. The highest and lowest values were at the 3rd and the 6th lactations, respectively. 

Therefore, it is reasonable to suppose that with increasing milk yield, the increased concentrations of plasma cortisol 

were associated with the increased demand of the mammary glands for cortisol for milk synthesis. Cortisol was 

higher in plasma (2 to 10 times) than in milk at all both temperature degrees and lactation numbers. 

Habeeb et al (1992) reported that cortisol level did not consistently increase when animals were exposed to moderate 

heat. Acute heat will significantly increase cortisol whereas prolonged heat is accompanied by slight declines in 

plasma level of cortisol. Plasma cortisol increased significantly in each of acute, chronic and prolonged heat. This 

contradiction in response of cortisol levels to change in ambient temperature may be attributed to the difference 

between animals in their heat tolerance. In addition, physiological state, production level, type of production, heat 

exposure period and blood sampling time also may be affect cortisol levels. Habeeb et al (2000) decided that the 

decline in T3 and the increase in cortisol in the heat stressed buffaloes during July month may be responsible for tire 

decline in milk components under such conditions. The relatively high total solids (fat, protein and lactose) 

percentage observed during February can be ascribed to the fact that those animals faced the favorable conditions of 

the mild winter season in Egypt. Habeeb et al (2000) showed that the buffaloes produced milk of a better quality in 

winter (at February) than that attained under summer conditions (at July). The higher ambient temperature of July 

month caused a significant decrease in milk total solids, butter fat, protein and lactose contents.  

Habeeb et al. (2007) showed that the stressful conditions induced significantly increases in heat shock proteins as 

well as urea-N and creatinine concentrations and significantly decreases in the levels of thyroxin and testosterone 

hormones as well as total protein concentration. The severe heat stress and heat stress conditions induced 

significantly decreases in the average daily body weight gain of buffalo calves when compared to either 

thermoneutral or mild climatic conditions. The same authors found that the percentage changes, due to stressful 

condition, in daily body weight gain were highly significantly correlated with the percentage change in each of heat 

shock proteins, thyroxin and testosterone and concluded that heat shock proteins or thyroxin or testosterone may be 

used, any one, as heat tolerance index to predict the heat adaptability of buffalo calves to reared in upper Egypt like 

Toshka area.  



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According to World Health Organization, World Meteorological Organization and the United Nations 

Environmental Program, global warming would be a greater frequency and greater duration of exposure to hotter 

temperatures, especially during the summer months. Typical hyperthermia sometimes occurs during severe heat in 

summer and as a result of hard expose to sun throughout the world. In animals and humans, some physiological and 

biochemical adaptations could occur to protect essential cell functions against heat stress and to permit a rapid 

recovery from moderate hypothermic damage (Hales, et al., 1996 and McMicael et al, 1996 ). 

 High ambient temperature during summer stimulates the peripheral thermal receptors to transmit suppressive nerve 

impulses to the appetite centre in the hypothalamus causing a decrease in feed consumption to minimize thermal 

load on animals. Thus, less substrate become available for hormone synthesis and heat production. Exposure to 

severe heat also suppresses the production of hormone releasing factors from the hypothalamic centers causing a 

decrease in pituitary hormonal secretion and consequently lowers the secretion of the thyroid hormones. The 

shortage of energy, substrates and T3 hormone may be responsible for the depression in milk yield and composition. 

In addition, high level of cortisol which was observed in the buffaloes exposed to high ambient temperature may be 

associated with the depression in quantity and quality of milk. From the economical point of view, it is concluded 

that due to exposure of 6 buffaloes to Egyptian summer heat conditions, the weakly milk production decreased by 

51.4 kg and 11 kg total solids loss in their milk. This means that their production benefits decreased weekly by about 

100.0 Egyptian pounds according to the price of 1996 (Habeeb et al., 2000). 

b. Thermoregulation in buffaloes: 

Animals maintain their heat balance through vasomotor control by regulating the amount of blood flowing through 

the cutaneous vessels by either vasodilatation or vasoconstriction. Vasodilatation stimulates the pilomotor centre to 

flatten the hair cover to allow better heat dissipation through conduction, convection and radiation (sensible means). 

In addition, some heat is lost by evaporation through the lungs and also from the surface of the body as a result of 

diffusion of water through the skin as insensible perspiration (Marai and Habeeb, 1997). 

When ambient temperature increases, the amounts of water lost by insensible perspiration are increases slightly until 

active sweating starts. The circulation of blood transfers heat from the core to periphery. Excess heat is dissipated by 

evaporation of sweat as a protective mechanism of the body against overheating. At the same time, respiration rate 

or panting increases and becomes shallower to permit an efficient ventilation of the upper respiratory tract, without 

undue overventialation of the lungs themselves (Shafei and Abdelghany, 1978). 

When the animal cannot sustain homoeothermic, it reduces the heat production using internal physiological means 

to help in re-establishment of the thermal balance. Feed consumption and thermogenic hormone secretion decrease 

to lower the basal metabolism resulting in a decline in productivity. If all these physiological mechanisms fail to 

balance the excessive heat load, the body temperature rises and the animal enters the acute phase of heat stress that 

normally occurs within a few days of the animal encountering the high temperature and is accompanied with a rapid 

decline in productivity. If these systems still fail to stop the elevation in body temperature, the animal succumbs 

with heat stroke and dies (Habeeb et al., 1992). 

c.Adaptation to hot climate: 

When exposing the animals to less severe hot conditions following more severe one or two intermittent heat stress 

between day and night and/or between seasons an acclimation to such renditions takes place and better productivity 

eventually stabilizes at a level greater than that observed before, but lower than the normal level. Some of these 

changes occur, rather rapidly (days), whereas others may require a longer period (weeks). When more favorable 

climatic changes occur, the performance is improved and a compensatory response occurs quite often resulting in a 

return to productive levels above the normal ones (Ames and Ray, 1983). 

Adaptation or the complex of processes by which an animal adapts itself to the hot environment (in which it has to 

live) depends upon either increasing heat loss, reducing heat production by decreasing the body's metabolic rate 

and/or increasing tolerance of its tissues to more fluctuating and high body temperatures by varying the body 

temperature, varying the tolerance to concentrations of salt in drinking water and decreasing water turnover by 

concentration of waste products in the urine in order to conserve body water, and to conserve nitrogen by recycling 

urea to adapt to lack of forage in the dry season. Yousef (1985) indicated that the physiological adaptations in the 

large part are due to changes in hormonal activity, particularly the decrease in thyro-adrenal activity. However, some 

physiological adaptations vary between species, between breeds within species and between individuals within breeds 

(forming the basis for the development of a new adapted breed). Natural selection for physiologically adaptive 

features with some assistance by man helped in manifestation such adaptations. Changes in the behavior of livestock 

are important in assisting adaptation. In the tropical environment, Livestock become more sluggish in their 

movements, thus reducing muscular heat production, besides that poultry hold their wings slightly separated when 

standing and adopt an extended position when lying down. Temperate type cattle seek shade more often during the 

day and graze at night and all livestock drink and use more water, under the same conditions. Intermittent heat stress 



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helps adaptation than more moderate continuous one, although it is difficult for the temperate breeds to adapt 

themselves to environments where the mean annual temperature is above 18°C (65°F). 

Generally, the heat tolerant animals are those which manifest the last changes in most of the physiological functions 

when subjected to hot climate, and the good management is that aims to facilitate adaptation 

Selection for adaptation of animals in hot climates 

Selection of desirable stock for the tropics or sub-tropics should be for animals physiologically equipped to withstand heat 

and drought, this could be achieved by selection according to morphological characteristic that can assist to adapt to hot 

climate and/or according to physiological parameters such as the actual response or adaptability to hot climate after 

testing the animals under the hot climate conditions. 

1. Selection based on the morphological characteristics: 

The morphological characteristics preferred to the hot climate breeds should include large skin area in relation to live 

weight, shielded eyes, pigmented skin and eyelids (to lessen susceptibility to eye cancer) and short sleek light colored hair. 

The ability of animals to shed their coats early in spring, to walk long distances, to adjust to low water intake, high intake 

of salts either in drinking water or in forages, to poor quality food and to harsh treatment and to resist ticks (animals with 

long or woolly coats pick up a larger number of larval ticks than animals with short sleek coats) and other pests, must be 

involved. 

With such information in mind, the breeds carrying bos indicus blood could be classified for different cattle areas in 

tropical and subtropical regions as follows: 

- Brahman for the extreme and very severe hot wet ticky regions. 

- Santa Gertrudis for ticky fairly severe hot wet and mixed (hot wet and hot dry) regions. 

- Africans for ticky hot dry regions. 

Regarding the European breeds (Bos Taurus), those with permanent short coats can be used in fairly hot rather humid 

regions and those with heavy coat, but shed early and decisively in the spring can be used in regions that are fairly hot and 

humid in summer. 

However, the spread of breeds to new areas may often be either a matter of chance or just trial and error, owing to the great 

complexity of the environment and the unexplained idiosynerasis of breed in respect to things like terrain. 

2- Selection based on physiological parameters: 

Proper and more accurate selection could be based on the ability of the animals to maintain expression of their inherited 

functional potential during their life-time when raised under the hot conditions (which is the typical definition of 

adaptability or heat tolerance). The relative changes in production, thermal, water and/or nitrogen balances of the animals 

in the conditions under which they have to live could be used in estimating parameters for detection of their adaptability. 

Such measurements are estimated following testing the animals in hot climates as shown below. 

 Parameters based on changes in thermal balance: 

1. Iberia heat tolerance (IHT; Rhoad, 1944): The test is carried out by keeping the animal in a cattle chute exposed 

to direct sunlight on a bright calm summer climate for three consecutive days with ambient temperature in shade between 

29 and 35°C. the averages of daily rectal temperatures (RT) and respiration rates (RR) measured at 10.00 and 15.00h are 

calculated. The IHT is estimated by the following equation:  

     IHT = 100 - 10 (RT - 101) where 101 = the average normal °F of rectal temperature in cattle. If two groups show the 

same coefficient, the one which has lower RR is considered higher in heat tolerance. Lee and Phillips (1948) made an 

improvement in IHT test by using a heat chamber to obtain standard conditions of temperature and humidity at 

which the animals are exposed for 6h. Bonsma (1955) opposed that between breeds there are significant differences 

in the standard temperature of the body fixed by Rhoad as 101°F and indicated that IHT is valuable in selection within 

breed for heat tolerance.  

2- Benezra index (BI; Benezra, 1954): The test is carried out by using RT and RR as shown in the following 

equation:  

       BI  = RT/38.3+RR/23  The values obtained above or below 2 represent lower or higher respectively, heat 

adaptability than normal. 

3. McDowell et al. (1955) used RT and RR response during 6h hot room test in estimating the relative response in 

cattle. The trapezoidal mean RT or RR during a 6h period (Tm) = (0.5 t 0 + t1 + t2 + t3 + t4 + t5 + 0.5 t6) / 6 where t1, t2, 

t3, t4 and t5 =RT or RR recorded after 1, 2, 3.... etc, h. of exposure. 

4. Bianca (1963) used the average final RT as heat tolerance coefficient (HTC) as follows: 

         HTC = 100 - 18 (Tr-38.3) where Tr = (average RT at comfort + Average RT at hot temperature)/ 2. In this index, 

the decrease in the final RT is accompanied with the increase in heat adaptability. Brown et al. (1969) indicated that the 

rate of RT rise is definitely related to heat sensitivity, and multiple measurements could be used as a test for heat 

sensitivity of individual animals. 

 



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Parameters based on productive responses: 

1- Milk yield, magnitude of rectal temperature and feed energy intake:  Milk yield (M), magnitude of RT and feed 

energy intake (F) could be used as an index for productive adaptability (PA) according to Johnson et al. (1988) as 

follows:  

PA = % increase in RT (% decrease in M + % decrease in F). Negative heat adaptability indicates heat sensitivity and 

is shown when percentage increase in RT is 2.4 or more and percentage decrease in M is 28 or more, while positive heat 

adaptability indicates heat tolerance and is shown when percentage increase in RT is 1.2 or less and percentage decrease 

in M are 8 or less. The PA index is more accurate estimation for the relative level of production potential in adverse hot 

climates and can provide a scientific basis for the establishment of improved strains for adverse climatic zones. 

 2- Daily body weight gain (DBWG):  Habeeb et al. (2007) showed that the stressful condition of severe heat stress 

(SHS) and heat stress (HS) induced significant reduction in DBWG of buffalo calves by 22.6 and 16.5%, 

respectively. The authors observed that there were individual variations in the amount of DBWG which decreased 

due to exposure of the calves to SHS or HS and consequently the percentage heat induced change differs from calf 

to another. Consequently, the heat adaptability (100- heat induced %) ranged between 83.9 and 31.4. Therefore, the 

first calf is the best calf while the second calf is the worst one. In this respect, Habeeb et al. (1992) and Kamal and 

Habeeb (1999) reported that the heat tolerant animals are those which exhibit the lesser changes in most of the 

physiological functions when subjected to hot climate. According to Kamal and Habeeb (1999) it can be concluded 

that first animal was more heat tolerant than second animal or the first animal is the most heat stressed calf because 

it lost more than 2/3 growth rate when reared under stressful conditions whereas the second calf is tolerated the heat 

better as it lost less than 1/6 of growth rate only.  

Habeeb et al. (2009) showed that the stressful condition of hot climatic conditions induced significant reduction in 

DBWG by 25.5%. Habeeb et al. (2007) found that exposed the buffalo calves to heat stress conditions of 36.0 and 

32.0 ºC induced significant reduction in DBWG by 22.6 and 16.5%, respectively, when compared to mild climate 

conditions (18.0 ºC). There are individual variations in the amount of DBWG which decreased due to exposure the 

calves to stressful conditions of summer season. The percentage decrease values ranged between 3.2 to 48.4. 

Consequently the heat adaptability (100- DBWG decrease %) differs from calf to another, so the percentage heat 

induced change in calf was 96.8 while in another calf was 51.6. This indicates that first animal growing under 

stressful conditions more than second one which showed more response to high temperature exposure. The authors 

concluded that the first calf was best while the second calf was worst one in the heat adaptability coefficient.  

Parameters based on changes in water balance: 

1- Total body water: Habeeb (1981) used the percentage increase in total body water (TBW) due to heat exposure 

as index for HTC as follows:  

    HTC - 100 - [(TBW2-TBW1) x 100 /TBW1 where TBW1 = TBW under comfort and TBW2 = TBW under hot 

conditions. The most heat tolerance animals are those with the highest values. Kamal (1982) and Kamal and Habeeb 

(1999) found a significant positive correlation between this index and the percentage increase in body weight gain 

during hot summer climate. 

2. Total evaporative rate: Yeck and Kibler (1958) used the ratio of total evaporative rate (TER) as index for HTC 

as follows:   

HTC = TER at 26.7°C: TER at 10°C.  The most tolerant animal is that shows the highest ratio, since evaporative is 

considered the sole mean of dissipating body heat at high ambient temperatures.  

3- Water turnover rate (water input or water intake): Kamal et al. (1978) used the percentage increase in water 

turnover rate (WTR) in estimating HTC as follows:  

      HTC = 100 - [(WTR2 – WTR1) x 100 / WTR1] where WTR1= WTR under comfort and WTR2 = WTR under hot 

conditions. WTR= Total body water (tritiated water space) x (0.693/ T½ x 24 h of day). The T½ (biological half-life 

time of tritiated water, 
3
TOH or 

3
HOH) = the time needed in days, to remove half total exchangeable body water pool 

and 0.693 = the tritiated water exponential disappearance rate constant. The most heat tolerant animals are those with 

the highest values, and that index has proved to be more accurate in determination of adaptability of animals than total 

vaporization.  

4. Biological half-life time of tritiated water (T½): Abdel-Samee (1982) used the percentage decrease in biological 

half-life time (T½) of tritiated water space (
3
HOH) due to hot conditions as an HTC index because T½ in animals depends 

on WTR, i.e. WTR increases and T½ decreases as the ambient temperature increases.  

HTC = 100 - [(T½1 - T½2) x 100 / T½1].  

Where T½1 of 
3
HOH under comfort and T½2 of 

3
HOH under hot conditions. 

Parameters based on changes in protein balance 

1. Nitrogen retention (NR): Kamal et al. (1962) used the percentage decrease in nitrogen retention [NR = (N intake 

x digestion coefficient) - N excretion] as HTC index as follows: 



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     HTC = 100 – [(NR1 - NR2) x 100 / NR1] where NR1and NR2 are nitrogen retention under comfort and hot conditions, 

respectively. The most heat tolerant animals are those with the highest values. 

2.  Lean mass: Kamal and Johnson (1970) used the loss in lean mass estimated by the loss in the amount of 

radioactivity naturally occurring in 
40

K in the body as a simple index for heat adaptability. The amount of 
40

K is counted for 

few minutes in the whole body counter before and after 3 days of heat exposure. From the 
40

K loss, the amount of lean 

mass loss can be known.  

     HTRC = 100 - [Body 
40

K under comfort - Body 
40

K under high temperature) x 100 / Body 
40

K under comfort]. The 

animal which loses less lean mass at high ambient temperature is considered as a heat tolerant. 

3.  Total body solids (Live body weight - total body water): Kamal and Johnson (1971) used the loss in total body 

solids (TBS) that include lean body mass and body fat as heat tolerance index. Total body water is determined before and 

after three days of heat exposure and each value is subtracted from the corresponding live body weight to obtain 

TBS under comfort and under hot climate.  

HTC = 100 - [(TBS at comfort - TBS at high temperature) x 100 / TBS at comfort]. The most heat tolerance animals 

are those with the highest values. 

4. TBW/ TBS ratio: TBW is determined before and after heat exposure and total body solids was determined by 

subtracting total body water from the corresponding live body weight to obtain TBS at TN and HS climates. TBW 

was divided by TBS under each of mild and hot conditions and the heat induced changes in TBW, l / TBS, kg was 

considered as heat tolerance index. This heat tolerance was found had significantly negative correlated with body 

weight gain (DBWG) in farm animals as follows:  

DBWG = 920.4 – 252.2 x TBW, l / kg TBS    [r = - 0.8925, P < 0.002](Kamal and Habeeb, 1999 and Habeeb et al., 

2001). 

5.   Protein catabolism: El-Fouly and Kamal (1979) used urea entry rate (urea pool size x 
l4
C-urea exponential 

disappearance rate) in blood as indication for protein catabolism in heat-stressed animals and as index for heat adaptability, 

since these values increase with different percentages in heat-stressed animals. Kamal (1976) used 15N-urea as an 

indication to protein catabolism instead of hazardous urea. Such method is quicker and more accurate than nitrogen 

retention method.  

Parameters based on changes in Blood volume and red blood cells volume: Shebaita and Kamal (1973) showed 

differences in heat tolerance between species and breeds due to differences in changes in blood volume and red blood 

cells volume in hot climate using radioactive sodium cremate. 

Parameters based on changes in DNA bases:   

Habeeb et al. (2009) used the heat induced changes in cyclic Guanosine MmonoPhosphate (cGMP) as heat tolerance 

index. The authors showed that heat-induced significant decrease in cGMP in plasma of animals as a function of 

heat stress. The averages cGMP concentrations during comfortable and hot climatic conditions were 100.8 and 76.8 

fmol / ml, respectively. The result showed that increase the ambient temperature from 24 to 36
o
C is followed by 

significantly increasing levels of the cGMP in plasma of calves by 23.34%. The percentage heat induced decrease 

differs from calf to another and ranged between 9.1 to 55.0. Consequently, the heat adaptability varied between 90.9 

which is the best calf and 45.0 which is the worst one. The heat adaptability index using cGMP had a highly 

significant positive correlation with DBWG and it can be concluded that cGMP is a good index for heat tolerance in 

growing animals. Habeeb et al. (2009) found that the highest value in the heat induced change in cGMP was 

observed in the animal which hade the lowest daily body weight gain.   

Parameters based on changes in protein fractions: 

1. Heat induced changes in total proteins:  

Habeeb et al. (2007) found that plasma total proteins values were 7.33 and 7.71 mg/dl in buffalo calves exposed to 

SHS (36oC) and HS (32oC) conditions and 8.32 and 8.50 g/dl when the calves exposed to comfortable conditions, 

respectively. The heat induced changes due to stressful conditions of SHS and HS as compared with comfortable 

conditions were 14.3 and 9.50%, respectively. Habeeb et al., (1992) clarified that the disturbance in protein 

metabolism occurred as a result of the depression in appetite and consequently less feed intake as well as the 

decrease secretion of anabolic hormones, especially thyroxin under hyperthermal conditions, may be responsible for 

the decrease in blood serum proteins in buffalo calves under SHS and HS. Habeeb et al. (2007) reported that plasma 

total proteins in buffalo calves decreased significantly during summer season of Egypt and the percentage decrease 

were 14.3 and 9.50 due to exposure the calves to 36 and 32 ºC, respectively, as compared to 18 ºC. The same 

authors found that the correlation total proteins and each of DBWG and HSP70 was not significant.  

Habeeb et al. (2007) reported that globulin values were 4.48 and 3.77 mg/dl in bovine calves exposed to comfortable 

and hot climates, respectively. The average heat induced decrease in the globulin due to stressful conditions was 

15.85%. The percentage decrease values ranged between 1.81% and 36.78% and the percentage heat adaptability 



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values ranged between 98.19% and 63.22, respectively. The percentage heat adaptability using globulin values had 

positive significant correlations with the percentage changes in each of DBWG.  

2. Heat induced changes in Heat shock proteins (HSP): Habeeb et al. (2007) showed that the stressful conditions 

of 36.0 and 32.0 ºC during summer season of Egypt induced significantly increases in HSP70 concentration in the 

plasma of buffalo calves and the percentage increase was highly significantly correlated with the percentage change 

in DBWG (0.971). Habeeb et al. (2007) showed that heat-induced heat shock (HSP70) protein expression in plasma 

as a function of heat stress. The authors showed that increase in the ambient temperature is followed by significantly 

increasing levels of the HSP70 in serum of buffalo calves. When considered mild climate as comfortable condition, 

the heat induced significantly increase in HSP70 by 494, 210% due to exposure of the calves to SHS and HS, 

respectively. The percentage heat induced change also differs from calf to another. Consequently, the heat 

adaptability (1000- heat induced %) may be used as the heat adaptability index or a god index for heat tolerance of 

growing buffalo calves. 

The heat-induced HSP70 protein expression in plasma as a function of heat stress was studied also by Habeeb et al. 

(2009). The predominant HSP70 protein band migrating under comfortable climatic condition is compared to that 

those under hot climatic condition in bovine baladi animals. The results showed that increase the ambient 

temperature from 24 to 36٥C is followed by significantly increasing levels of the HSP70 in plasma of bovine baladi 

calves by 17.5% with differs from calf to another. The percentage increase was 3.35 % in calf while it was 58.29% 

in another calf and consequently, the heat adaptability was 96.65% in the first calf and was 41.71 in the another one, 

i.e. the first calf is the best while the second is the worst one. The heat adaptability index using HSP70 was parallel 

with that obtained by daily body weight gain (DBWG) and  had a highly significant positive correlation with 

DBWG (0.797) and it can be used HSP70 as good index for heat tolerance in growing animals.  

Habeeb et al. (2009) showed that heat-induced HSP90 protein expression in plasma as a function of heat stress. The 

predominant HSP90 protein band migrating under comfortable climatic condition is compared to that those under 

hot climatic condition in animals. The results indicated that the increase the ambient temperature from 24 to 36٥C is 

followed by significantly increasing levels of the HSP90 in plasma of calves by 19.62%. The percentage heat 

induced increase was 1.34% in calf while it was 50.82% in another calf and consequently, the heat adaptability was 

98.66% in the first calf and was 49.18 in another calf. The heat adaptability index using HSP90 had a highly 

significant positive correlation with DBWG (0.867) and may be using HSP90 is a good index for heat tolerance in 

growing calves. 

Parameters based on changes in hormonal level: 

1. Heat induced changes in Thyroid hormones: Habeeb et al. (2007) showed that the stressful condition of SHS 

and HS induced significantly decreases in T4 levels by 30.8 and 18.2 %, respectively. The percentage heat induced 

changes were 25.0 and 70.0 and consequently, the heat adaptability was 75.0 in the first calf (the best calf) and was 

30.0 in the worst calf.  The lower levels of T4 in the heat stressed calves may be associated with the decreased 

animal heat production under hot conditions in order to maintain homeostasis (Habeeb et al., 1992).  

The heat-induced changes in both T3 and Cortisol hormones were significantly correlated with daily body weight 

gain (DBWG) in heat-stressed animals (Habeeb et al., 2001). The two equations as follows: 

DBWG = 997.8 – 12.5 x ng / dl decrease in T3 [r = - 0.881, P< 0.003] 

 

DBWG = 978.5 – 88.3 x ng/ ml increase in Cortisol [r = 0.7945, P < 0.01].  

  

Therefore, Habeeb et al. (2001) used the heat induced changes in each of the two hormones as heat adaptability 

index for predicting the growth rate of animals under heat stress conditions. The highest values in the heat induced 

changes in each of T3 (ng/dl) and Cortisol (ng/ml) were observed in the animals which have the lowest daily body 

weight gain. 

2. Heat induced changes in Testosterone hormone:  

Habeeb et al. (2007) reported that the stressful condition of SHS and HS induced significantly decrease in 

testosterone levels by 33.1 and 21.5 %, respectively. The percentages heat induced changes were 10.0 and 93.3 and 

consequently, the heat adaptability percentages were 90.0 and 6.7. The lower levels of testosterone in the heat 

stressed calves may be associated with the decrease of gonadotropin releasing hormone secretion from the pituitary 

gland of heat stressed animals (Habeeb et al., 1992).    

Management of livestock in hot climates: 

Optimal climatic conditions for cattle, buffaloes, sheep goats, pigs, rabbits and poultry would be something like an air 

temperature of 13 to 20°C, a wind velocity of 5 to 18 km/hr, relative humidity of 55 to 65% and a moderate level of sunshine. 

However, these factors are interrelated. 



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In view to breeds of animals suitable for the tropics or sub-tropics, some areas or countries are favored with their own 

indigenous breeds, where there is stability in the sense that the stock survive and reproduce despite the climatic rigours, but 

with, generally, a low level of production Other areas have had to rely entirely or partially on introduction of higher 

productive tropical or temperate type breeds, that can be raised as purebreds or crossed with the native stock. In the latter 

case, deliberate measures must be taken to select and breed animals specially fitted for each difficult region as 

mentioned by Habeeb et al. (1997). In addition, the possibility of a breed to fit in a certain region can be evaluated 

by constructing climographs (Wright 1946 and 1954) using climate data collected from both the original and new 

environments by plotting the mean monthly air temperature against the mean monthly relative humidity. Similarity of 

position, shape and area of the two patterns so formed after joining the twelve points, indicates such possibility. However, 

disease and parasite criteria, the feed situation, prices of inputs and products and the market situation also, have to be 

considered, in this respect. 

The selected breed for a certain region should manifest the least changes in most of the physiological functions and 

consequently in die productive and reproductive traits, under the new environment. In addition, when importation of the 

breed into a new environment is contemplated, a large number of animals of the same breed but from different areas or 

countries must be included, to give more chance as much as possible genotypes for reaction with the environment. The sires 

selected should be of high productivity and imported from different herds or countries to avoid inbreeding that occurs inevitably 

in the small populations. In addition, each sire should be used for mating a group of unrelated females for one year, and then 

shifted rotationally to the other groups for the same reason. Such practice could be carried out up to the three generations 

at least, before the use of each sire or it's off springs with its original group. Transport of that breed from its original 

homeland should be carried out during the mild weather of the year in the new locality, i.e. during winter, in order that the 

animals can habituate gradually with the onset of summer hot climate. It is also preferred to locate that breed in areas with the 

mildest climate in the new country and to arrange achieving parturitions of the animals during the mild climate season of the 

year to avoid summer sanitary problems for the youngest. 

With regard to housing, shade is the simplest and a relatively inexpensive tool for combating heat. A shed should be placed on 

a top of a hill if possible, open on all sides and with wire or cable fences, the roof should be 3.5 to 4.0 meters high with its long 

dimension east-west to prevent exposure to high sun radiation. The roof slopes should be south - north to avoid vertical sun heat. 

The roof can be made of a 10 to 15 centimeters layer of hay held in place by wire above and below that realizes 

insulating and cool effects (Marai et al., 1992 and Yousef et al., 1996 & 1997). Such roof do not permit penetration 

of heat from the sun through to radiate into the animals, as well as, little radiant heat from the animals is reflected 

back from its underside. In addition, hot air under the shade can rise up through the loose hay. If solid insulating material or wood 

shade roofs are used, the top should be painted white or shiny to reflect as much heat as possible, and the underside 

should be dull and dark to avoid reflecting animal heat it receives. The pens should be constructed of wire or cables 

to offer less resistance to air movement. The adequate surface area from shade per animal is 3.7 - 5.6 square meters for cattle 

and 1.86 - 2.79 square meters for sheep and hogs to be kept loose in the shed. Vegetation should surround the pens. Shade 

trees (with falling leaves during winter) should be scattered around and within the yards of the sheds, and such sheds 

should be scattered in the pasture or range. If livestock owners are compelled to build for housing their animals, they 

have to use insulating materials for the outer walls with adequate ventilation openings and the roofs should erect 60 

centimeter more than the outer walls to protect the walls from direct sun heat. This is in addition to application of all that 

mentioned in establishing the sheds. 

Regarding feeds and feeding, proper requirements should be offered to animals all the year round. Protein content often 

averages 2-4 percent in deceptively lush-looking grown in there areas. Such forage is usually mature and dry out with a high 

stem: leaf ratio (due to falling of the leaves while drying).- Digestion of highly lignified fibrous feeds increases the heat output 

and heat load at a time the animal is already under considerable heat stress. Animals efficient in feed conversion have more ability 

to withstand heat stress effects, since they produce less heat while digestion of such feeds. Arranging feeding with minimum 

lignified feeds and / or containing ingredients with low fiber-high energy content produces less metabolic heat is beneficial in such 

areas (Beede and Collier, 1986). As a general rule, feeds should be administered during the coolest periods of the day, i.e. at 

early morning, late in the evening or by night, under hot climate conditions. In extremely hot days, it is preferred to keep the 

animals in the sheds. 

With regard to drinking water, ample fresh cool water must be found within each shed. The water troughs and the animals 

while watering should be shaded by a suitable shelter from the direct sun heat, and the water pipes should be placed at 20 - 25 

centimeters depth from the ground surface to keep the water cool in the hot climate. Internal and external parasites, fungi and 

disease vectors that prevail in high ambient temperatures and humidities require rotational treatments for prevention and 

adequate facilities for treatments when the animals are infested. This is in addition to application of the known sanitary 

measures. 



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The low degree of technical skill in livestock rising is another problem in such regions. Regular training of those who are 

concerned on the proper methods for animal husbandry will help in overcoming such disadvantage. The specialized institutions 

spread in the country side, may play the major role in this respect. 

Methods for alleviation the heat stress conditions on animals: 

Environmental amelioration practices arc usually applied to highly intensive enterprises, of which products bring in 

sufficient return to warrant the expenses, e.g. dairying, feed-lot production or poultry keeping. Some of the management^ 

practices to ameliorate the environment and reduce the animal's heat production, are shown above. 

Below, arc some techniques that can be used to help the animal in dissipating the heat load and to correct the negative effects 

caused by heat stress. Such techniques arc classified to physical, physiological and nutritional techniques as follows. 

     a. Physical techniques: 

1. Air movement: Increasing air movement promotes evaporation, makes cooling by perspiration more effective and 

helps removal heat dissipated by animals in the form of radiation, conduction and convection. It can carry away 

moisture in the form of vapor. It also helps in cooling of the surroundings (bam walls and roofs, fences, earth  ... etc) 

which in turn helps keeping the animals cooler. 

2. Air conditioning: The air condition technique improves each of growth and milk yield and its composition of heat 

stressed animals. However, it has not, practically, been established as an economically feasible tool in hot weather 

because of the high costs of electrical power supply (Kamal et al., 1972). The techniques 1 and 2 arc considered as 

methods of modification of the environment as well. 

3- Sprinkling (spraying). The importance of sprinkling in dissipating heat load is due to the high thermal capacity of 

water (1 cal / gm /°C) and its high heat of evaporation (580 cal/gm). Sprinkling the animal with water would help in 

dissipating heat from the skin of the animal through conduction and then evaporation of the water layers coating it 

(Kamal et al., 1989 and Marai et al., 1995 & 1997). 

4. Drinking cool water: The beneficial effect of drinking cool water in reduction of the heat load is due to the heat 

dissipated by conduction as a result to the difference between the drinking cool water and urine temperatures. 

Moreover, the increase in body water due to the increase in water intake under hot climate helps dissipation of heat 

by increasing evaporative heat loss through sweating and respiration and by conduction (Habeeb et al., 1994 and 

Marai et al., 1997). 

5- Clipping: Significant reduction in skin and rectal temperatures and respiratory rates has been shown by clipping 

animals (Bianca, 1959). In range and housed conditions, shorn animals show an increase in growth rate. However, 

the direct exposure of their clipped skins to solar radiation may hurt the skin. In such case, suitable covering for the skin 

can be obtained by partial clipping of the coats of the animals. 

b. Physiological techniques: 

1- Diaphoretics administration: These compounds are used to increase sweat production for increasing the evaporative 

cooling of the heat stressed animals (Kamal et al., 1972 and Marai et al., 1995). However, such treatments cause 

significant increases in each of rectal temperature and respiration rate. 

2- Diuretics administration: These compounds are used to increase water excretion to increase the heat loss by 

excreting water in urine with the same body temperature and then followed by drinking water which is also of lower 

temperature than that of the body (Daader et al., 1989). 

3- Goitrogens administration: These compounds block thyroidal iodine uptake and consequently depress thyroid 

gland activity. It depresses the secretion of T4 in the heat stressed animals to decrease heat production. However, 

this technique is not favored under heat stress conditions, since the treated animals under such conditions may be 

affected seriously due to their need to more energy for greater muscular activity for the high respiratory activity, O2 

consumption and energy metabolism (El-Fouly, 1969 and Kamal et al., 1972). 

 4. Hormonal substances administration: Administration or injection of hormones can be used as a technique for 

alleviation of heat load on animal since secretion of most of the hormones is depressed under heat stress conditions. 

However, injection of 74 for this purpose was found to be associated with the increase of body temperature of the 

animals (Marai et al., 1994). Similarly, insulin injection in the udder was found to show the same effect, besides it 

increases milk production. Injection by BST also minimized the negative effects of moderately high environmental 

temperatures on milk yield by increasing heat loss and minimizing the endogenous heat production and related physiological 

functions without any significant increase in rectal temperature and respirator v rates (Mohammed and Johnson, 1985). 

However, such techniques require some specific precautions and arc expensive at the same time. 

c. Nutritional techniques: 

Supplementing of heat stressed animals with protein, fat and/or mineral resources, is  required to correct their negative 

balances, since heat stress induces a significant decrease in the dry matter intake and a significant increase in protein and 

lipids catabolism and decrease in live body weight, in addition to increase in excretion of urine and sweat containing 

minerals. Supplementation with ingredients that include crude protein or NPN (like urea) can be used to correct the negative 



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nitrogen balance (Habeeb et al., 1989 and Marai et al., 1997). Palm oil can be used to increase the gross energy intake 

and consequently increase the performance. Mineral resources supplementation corrects minerals negative balances 

(El-Masry et al., 1989). 

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