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Thermoadaptability of Stud Bulls using Heat Tolerance Indices under Heterologus Climate

Tripti Kumari Subhransu Pan Debasish Satapathy Rajeev Kumar Choudhary Beena Sinha
Vol 8(1), 47-54

Present experiment was conducted on 25 stud bulls (5 from each genetic group belonging to Sahiwal, Gir, Jersey cross, Holstein-Friesian cross and Murrah buffalo bull) at Frozen Semen Bull Station, Haringhata, Nadia (West Bengal) in two seasons, viz., winter and summer to study their thermoadaptability under heterologus climate. Rectal temperature, pulse rate and respiration rate of bulls were recorded in forenoon and afternoon and three heat tolerance indices (Iberia heat tolerance indices, Benezara coefficient of adaptability and Dairy search index) were calculated as per formula. Significant (P<0.01) variations among genetic groups, seasons and genetic groups within a season were observed in all the three methods of thermoadaptability estimation. Rank of a particular genetic group with respect to heat tolerance capability was not same in all the three methods. During summer season heat tolerance indices showed higher deviation from their respective values of perfect thermoadaptability as compared to that of winter season. Bulls found to be more adaptable in winter season as compare to summer season.

Keywords : Heat Tolerance Indices Thermoadaptability Stud Bulls Season


Stress is seen upon as a symptom resulting from exposure of an animal to a hostile environment.  Variance in heat tolerance capability of bulls might be attributed to the differences of magnitude of change in physiological responses to similar kind of stressors which depend upon individual adaptive ability. Bulls regulate internal body temperature by matching the amount of heat produced through metabolism with the heat flow from the animal to the surrounding environment. Heat flow occurs through processes dependent on surrounding temperature (sensible heat loss; i.e. conduction, convection, radiation) and humidity (latent heat loss; evaporation through sweating and panting). The climate in a certain geographical area, particularly temperature and relative humidity greatly influence the reproductive potential of the bulls. When breeds/genetic groups are relocated from their native climate to other climate the new climate could be termed as heterologus climate for the breeds. In the heterologus climate the breeds/genetic groups possibly have to face varying degree of thermal stress (Hansen, 1990). This thermal stress could be either heat or cold stress. Thermoadaptability of bulls is a necessary factor under tropical environmental conditions to remain free from these kinds of thermal stresses (Mandal and Tyagi, 2008).

Stud bulls are mainly reared for the breeding purpose and breeding behaviour of bull is closely associated with adaptability. Although various genetic group of bulls that are maintained at breeding studs have different adaptability level. Adaptability is the capacity of a system to withstand a hostile environment without significant impairment of its normal operations (Azam et al., 2012). Genetic group differences and climate has a significant effect on adaptability (Hansen, 2004). Poor thermoadaptability of bulls in a heterologus climate is a limiting factor for optimum production and reproduction performances. Evaluation of thermoadaptability of stud bulls is an essential prerequisite for selection of animals, formulation of suitable breeding plans, estimation of production and reproduction efficiencies etc.

Therefore, present study aimed to evaluate thermoadaptability of stud bulls using various heat tolerance indices under heterologus climate so that better management practices can be planned against these stresses which  helps the animal to be adaptable as well as perform better in the tropical area.

Materials and Methods

The experiment was conducted at Frozen Semen Bull Station, Haringhata Farm under Paschim Banga Go Sampad Bikash Sangsthan, ARD Department, and Government of West Bengal, India.

The present study has been carried out on twenty five stud bulls belonging to five genetic groups viz., Sahiwal, Gir, Holstein-Friesian cross, Jersey cross and Murrah Buffalo, maintained at Frozen Semen Bull Station, Haringhata Farm, Nadia (West Bengal).  Five bulls of each five genetic group were identified giving emphasis on identical body weight (within genetic group) and age as much as possible. Animals were maintained as per routine management practices of Frozen Semen Bull Station in uniform environment and identical conditions.  They were housed in asbestos roof byre with concrete floor and pucca walls. Each animal was placed in individual stall with sufficient ventilation and natural light. Bulls were put to exercise in the morning daily. They were given cold water bath in the early hours of the day. In summer season, bulls were given water bath twice a day, once in morning and second in afternoon before offering feed.

Health Management

Bulls were vaccinated against H.S., B.Q., Anthrax and F.M.D. Crossbred bulls were additionally vaccinated against Theileria. As a routine health check measure, rectal temperature of all the bulls was recorded daily.

Seasons of Observation

The observations  were recorded in two seasons, viz., winter, (from 15th January to 15th February, 2014 )  and summer (5th  May  to 5th June, 2014).  Ten sets of observation on each bull were recorded in each season. Total 50 observations on each genetic group were recorded in each season. Thus a total of 250 observations in each parameter were recorded in each season.

Table 1

Meteorological Observation

Meteorological data pertaining to both experimental seasons were collected from the Observatory managed by the Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia (W.B), India. The Observatory is located within 1.0 km radius of bull station. Temperature humidity Index (THI) (morning and afternoon) has been calculated as per NRC (2001) using following formula.

THI = 0.72 (Cdb + Cwb) + 40.6

Where, Cdb and Cwb = dry and wet bulb temperature in centigrade respectively.

Heat Tolerance Coefficient 

Heat tolerance coefficient of bulls have been measured as per methods of Iberia heat tolerance coefficient (Rhoad, 1942), Benezara coefficient of adaptability (Benezara, 1954), Dairy search index (Bonsma, 1949). Rectal temperature, pulse rate and respiration rate was recorded in the morning at 6.00 to 7.00 A.M and again in afternoon at 1.30 to 2.30 P.M on the bulls under observation. Heat tolerance coefficients were calculated using following formulae.

Iberia Heat Tolerance Coefficient (IHTC)

IHTC = 100-10(BT-101)

where BT is the body temperature (oF). Average value of rectal temperature at 6.00 to  7.00 A.M and 1.30 to 2.30 P.M of a day was taken as BT. An ITHC value of ‘100’ indicates the measures of perfect adaptability.


Benezara Coefficient of Adaptability (BCA)

BCA =BT/38.33 + NR/23

where BT is the body temperature (0C) and NR is the respiration rate/min (average of 6.00 to 7.00 A.M and 1.30 to 2.30 P.M). An increase in        co-efficient from ‘2’ indicates reduction in thermal adaptability.

Dairy Search Index (DSI)

DSI = 0.5(X1/X) + (0.2 (Y1/Y) + 0.3 (Z1/Z)

where X1, Y1 and Z1 are the observed rectal    temperature (0C), respiration rate and pulse rate (per min) respectively. X, Y, and Z are     normal temperature, respiration and pulse rate (per min). An increase in DSI value from ‘1’ indicates decrease in thermal adaptability.

Statistical Analysis

To study the effect of genetic factor like bull and non genetic factor like season on heat tolerance coefficients the data were analyzed using mixed model least squares analysis for fitting constants (Harvey, 1990).

The mathematical model used to study the effect of different factors was as follows –

Yijk = μ + Bi + Sj + (B×S)ij + b1(XijkX ) + b2 (XijkX ) + b3 (XijkX ) + eijk

Where, Yijk is the record for the kth animal. μ is the overall mean, Bi is the random effect of the ith genetic group, Sj is the effect of the jth season of sampling, (B×S)ij is the interaction effect of the genetic group of animal and season of sampling, b1 is the linear regression coefficient for temperature during sampling, b2 is the linear regression coefficient for humidity during sampling, b3 is the linear regression coefficient for temperature humidity index (THI) during sampling, Xijk is the temperature, humidity and THI respectively corresponding to Yijk., X is the arithmetic mean of temperature, humidity and THI respectively during sampling, eijk is the residual error element with standard assumptions.

Mean and standard error of the traits were calculated using standard statistical procedure. Other statistical analysis like correlation etc. was calculated as per standard statistical techniques (Snedecor and Cochran, 1967).

Results and Discussions

Heat tolerance indices of individual bull in various methods of thermoadaptability estimation are given in Table 1. Ranking of bull on the basis of Heat tolerance coefficient (Mandal and Tyagi, 2008) are shown in Table 2. Degrees of deviation in thermoadaptability of bulls are presented in Table 3.



Table1:  Heat tolerance indices of bull (Mean ± S.E.)

Genetic Groups Seasons Iberia Heat Tolerance Coefficient (IHTC) Benezara Coefficient of Adaptability (BCA) Dairy Search Index (DSI)
Sahiwal Winter 101.8±0.60a 2.06±0.01a 0.86±0.002a
Summer 91.37±0.60b 2.32±0.01b 0.96±0.002b
Overall Mean 96.61±0.34ACEF 2.19±0.01ACDE 0.91±0.001ABDF
Gir Winter 101.94±0.60c 2.07±0.01c 0.90±0.002
Summer 92.16±0.60d 2.30±0.01d 0.95±0.002
Overall Mean 97.05±0.34EHLO 2.19±0.01DHKN 0.93±0.001EJNR
Jersey cross Winter 101.62±0.60e 2.02±0.01e 0.86±0.002c
Summer 89.52±0.60f 2.34±0.01f 0.96±0.002d
Overall Mean 97.52±0.34DGMN 2.18±0.01CGKL 0.91±0.001CHOP
Holstein-Friesian cross Winter 99.71±0.59g 2.01±0.01g 0.85±0.002e
Summer 89.87±0.60h 2.35±0.01h 0.98±0.002f
Overall Mean 94.79±0.34BGIJ 2.17±0.0BGHI 0.92±0.001AIKL
Murrah Winter 101.55±0.60i 2.12±0.01i 0.91±0.002g
Summer 86.44±0.60j 2.40±0.01j 1.01±0.002h
Overall Mean 96.49±0.34FKN0 2.26±0.0FJMO 0.96±0.001GMQS

Mean having different superscript (in capital letters) within the same column differs significantly (P<0.01) and (in small letters) within the same column differs significantly (P<0.05).


Table 2: Showing rank of thermal adaptability of bulls on the basis of heat tolerant indices

Genetic Groups Iberia heat tolerance coefficient (IHTC) Rank based on IHTC Benezara coefficient of adaptability (BCA) Rank based on BCA Dairy Search Index (DSI) Rank based on DSI Remarks
Sahiwal 96.61±0.34 ** -3 2.17±0.01 *** -2 0.91±0.001 *** -1 Good thermoadaptable
Gir 97.05 ±0.34 *** -2 2.18±0.01 ** -3 0.92±0.001 ** -2 Good thermoadaptable
Jersey cross 97.52±0.34 *** -1 2.16±0.05 *** -1 0.91±0.01 *** -1 Good thermoadaptable
Holstein-Friesian cross 94.79±0.34 # -4 2.19±0.01 # -4 0.93±0.001 # -3 Poor thermoadaptable
Murrah 96.49±0.34 # -5 2.26±0.01 # -5 0.96±0.001 # -4 Poor thermoadaptable

*** More heat tolerant , ** Fair heat tolerant,  # Poor heat tolerant

As it is evident from the result that the overall Iberia heat tolerance coefficient irrespective of season were found highest in Jersey cross (97.52±0.34) followed by those in Gir (97.05±0.34), Sahiwal 96.61±0.34, Murrah 96.49±0.34 and Holstein-Friesian cross 94.79±0.34 in that order. Overall Benezara coefficients of adaptability irrespective of season were highest in Murrah (2.26±0.01) followed by Gir and Sahiwal 2.19±0.01, Jersey cross 2.18±0.01 and Holstein-Friesian cross 2.17±0.01 in that order. And the overall Dairy search index  irrespective of season were found highest in Murrah 0.96±0.001 followed by those in Gir 0.93±0.001, Holstein-Friesian cross 0.92 ±0.001 and Jersey cross and Sahiwal 0.91±0.001 in that order.

Table 3: Degrees of deviation in various thermo-adaptability indices of bulls during two seasons

Genetic Groups Seasons Iberia  Heat Tolerance Coefficient (IHTC) Benezara Coefficient of Adaptability (BCA) Dairy Search Index  (DSI)
Sahiwal Winter 101.8±0.60 2.06±0.01 0.86±0.002
-1.80% -3% (–)
Summer 91.37±0.60 2.32±0.01 0.96±0.002
-8.63% -16% (–)
Gir Winter 101.94±0.60 2.07±0.01 0.90±0.002
-1.94% -3.50% (–)
Summer 92.16±0.60 2.30±0.01 0.95±0.002
-7.84% -15% (–)
Jersey cross Winter 101.62±0.60 2.02±0.01 0.86±0.002
-1.62% -1% (–)
Summer 89.52±0.60 2.34±0.01 0.96±0.002
-10.48% -17% (–)
Holstein-Friesian cross Winter 99.71±0.59 2.01±0.01 0.85±0.002
-0.29% -0.50% (–)
Summer 89.87±0.60 2.35±0.01 0.98±0.002
-10.13% -17.50% (–)
Murrah Winter 101.55±0.60 2.12±0.01 0.91±0.002
-1.55% -61% (–)
Summer 86.44±0.60 2.40±0.01 1.01±0.002
-13.56% -20.9 (–)

Figures in parenthesis indicated the % deviation from the perfect thermoadaptability index

The effects of genetic group, season and genetic group x season interaction were significant statistically (P<0.01). However DMRT reveals that only the difference between Holstein-Friesian cross and Sahiwal., Jersey cross and Sahiwal, Murrah and Sahiwal., Holstein-Friesian cross and Gir, Holstein Friesian cross and Murrah, Jersey cross and Gir, Jersey cross and Murrah, and Gir and Murrah were significant statistically (P<0.05). Rest of the effects were found to be non significant. It indicated that response of individual genetic group to the thermal stress was not same under the similar conditions.

Individual bulls were ranked for heat tolerance capability (from most to least) and it was not uniform in all the three methods of thermoadaptability estimation. This might be due to the differences in the magnitude of changes in physiological responses to similar kind of stressors, which depends upon individual adaptive ability. After ranking for heat tolerance, bulls were catogerized as good and poor heat tolerant bulls. Among the genetic group studied, Sahiwal, Gir and Jersey cross have shown good thermoadaptability, where as Holstein-Friesian cross and Murrah buffalo have shown poor thermoadaptability. This finding was supported by Mandal and Tyagi (2008) and Gaughan et al. (2012).

Degree of deviation in thermoadaptability from most perfect value (100%) was calculated in terms of percentage in two seasons. During winter and summer season, in case of Sahiwal, Iberia heat tolerance coefficient was deviated by 1.8 and 8.63%, Benezara coefficient of adaptability 3 and 16 % respectively and no deviation occurs in Dairy search index during these seasons.  In case of Gir, Iberia heat tolerance coefficient was deviated by 1.94 and 7.84%, Benezara coefficient of adaptability 3.5 and 15% respectively and no deviation occurs in Dairy search index during these seasons. In case of Jersey cross, Iberia heat tolerance coefficient was deviated by 1.62 and 10.48%, Benezara coefficient of adaptability 1 and 17% respectively and no deviation occurs in Dairy search index during these seasons. In case of Holstein-Friesian cross, Iberia heat tolerance coefficient was deviated by 0.29 and 10.13%, Benezara coefficient of adaptability 0.5 and 17.5% respectively and no deviation occurs in Dairy search index during these seasons. While in case of Murrah buffalo bull, Iberia heat tolerance coefficient was deviated by 1.6 and 13.56%, Benezara coefficient of adaptability was deviated by 61 and 20% respectively and no deviation occurs in Dairy search index during the winter season where as 1% deviation occurs during the summer season. Although during summer, the magnitude of deviation was high as compared to that in winter season. The heat tolerance coefficients were almost nearer to the perfect values during winter season. The mean rectal temperature, respiration rate and pulse rate /min. during summer were 1.230C, 85.32% and 44.01% higher than winter season. Thus, result indicated that summer was the most stressful season for the bulls. The variation found might be due to failure of the bulls to acclimatize with stressful weather conditions and it resulted in increment in thermal load and deviation from perfect values of thermoadaptability. Similar findings were reported by Chen et al., 1993 and Thomas and Acharya, 1981 in exotic and crossbred cattle and Mandal et al., 2002 and Mandal and Tyagi, 2008) in Frieswal bulls.


Present study revealed that bulls can be categorized as good and poor thermoadaptable on the basis of heat tolerant indices. Genetic group, seasons and genetic group with in a season had significant variation on thermoadaptability of bulls and also rank of a particular genetic group with respect to heat tolerance capability was not same in all the three methods of thermoadaptability estimation. Holstein-Friesian cross and Murrah buffalo bulls are more affected by heat stress than Sahiwal, Gir and Jersey cross bulls. As per physiological response and thermal tolerance summer was very stressful and winter was comfortable for the bulls.


Authors are thankful to the Director, Frozen Semen Bull Station, Haringhata farm, Nadia (West Bengal), India for carrying out the work. It is also acknowledged that the Head, Department of Animal Sciences, Bidhan Chandra Krishi Vishwavidyala, Mohanpur, Nadia (West Bengal), India has supported in providing meteorological data required for the study.


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