The study was conducted to observe the effect of seasons on thermoregulation responses. A total of 100 cows including 50 Sahiwal and 50 Karan Fries cows were selected from Livestock Research Centre of ICAR-National Dairy Research Institute, Karnal, India. The study was conducted during winter (THI=49.67±1.18), spring (THI=64.65±0.41) and summer (THI=87.28±1.26) seasons. Changes in RR, RT and HTC were observed in different seasons in Sahiwal and Karan Fries cows. In Sahiwal cows RT (°C) during winter, spring and summer were 37.300±0.095c, 38.178±0.095b and 38.810±0.095a respectively whereas RT (°C) in Karan Fries were 37.492±0.115c, 38.398±0.115b and 39.186±0.115a during winter, spring and summer respectively. RR (breaths min-1) in Sahiwal cows during winter, spring and summer were 15.738±0.795c, 18.158±0.795b and 29.818±0.795a respectively whereas RR in Karan Fries during winter, spring and summer were 15.779±1.136c, 22.979±1.136b and 47.299±1.136a respectively. The magnitude of increase in RR, RT and HTC were found to be higher during summer compared to other seasons in both Sahiwal and Karan Fries cattle. It was observed that Sahiwal cows are less sensitive and are better able to regulate body temperature in response to heat stress than Karan Fries cows.
Climate change poses formidable challenge to the development of livestock sector in India. Adaptation to heat stress imposes physiological, behavioral and metabolic adjustments to reduce the strain and enhances the likelihood of surviving the stress (Bernabucc et al., 2010). Physiological tolerance of dairy cows is a strong determinant of the environmental conditions in which they inhabit. Like other homeotherms, cattle regulate their body temperature at certain range of environmental temperature with least involvement of thermoregulatory mechanism (Aarif et al., 2013). This range of ambient temperature is called zone of thermo neutrality (Hansen, 2004). When environmental temperatures are below or above thermo neutral zone, dairy cows begin to experience either cold stress or heat stress. The physiological stress due to adverse climatic condition has great economic impact in dairy animals effecting the production or reproductive efficiency including health and capacity of resistant to disease (Aarif and Mahapatra, 2013). Under thermal stress, there is differences in a number of physiological and behavioral responses due to variation in animal genetic make-up and environmental factors through the integration of many systems and organs viz. physiological, behavioral, cardio-respiratory, endocrine and immune system (Altan et al., 2003; Kumar et al., 2011; Ganaie et al., 2013). Sweating, increased respiration rate and rectal temperature, decreased DM intake and efficiency of feed utilization, reduced metabolic rate and altered water metabolism are the physiologic responses that are associated with negative impacts of heat stress on production and reproduction in dairy animals (West, 2003; Ganaie et al., 2013). The indigenous Zebu breeds (Bos indicus) of cattle are better able to regulate their body temperature in response to thermal stress compared to European breeds (Bos taurus) due to their long time adaptation with tropical climates (Beatty et al., 2006; Gaughan et al., 2010). Zebu (Bos indicus) breeds have low metabolic rate and great sweating capacity (Hansen, 2004), but generally they exhibit low productive and reproductive performance (Ageeb and Hiller, 1991). Crossbreeding of cattle has been adopted for blending the adaptability of tropical cattle with the high milking potential of exotic breeds (Musa et al., 2008; Abdelatif and Alameen, 2012). The problem of heat stress in dairy cattle has recently received more attention because of anticipated increases in environmental temperature by global warming (Hansen, 2004; Hoffmann, 2010). Improving the knowledge of physiological and metabolic mechanisms of adaptability may contribute to the development and adoption of procedures viz. managerial, nutritional and genetic that may help to maintain reproductive and productive efficiency in high-yielding dairy cows and the health status of animals living in hot environments (Bernabucc et al., 2010).
Materials and Methods
Animals and Management
The study was conducted on randomly selected 100 cows i.e., 50 Sahiwal and 50 Karan Fries (Holstein Friesian X Tharparkar) cows maintained at Livestock Research Centre of ICAR-National Dairy Research Institute, Karnal. All the animals were maintained as per standard feeding and management practices followed at farm. The animals were clinically healthy and kept under the same conditions, with appropriate facilities for feeding and watering.
The experimental design and procedure were carefully planned and approved by the Institutional Animal Ethics Committee. The effect of season (winter, spring and summer) and physiological status of dairy cows on thermoregulation was assessed. In each season, both respiration rate (RR) and rectal temperature (RT) were recorded for all the dairy cows.
The outdoor temperature and the relative humidity (RH) (%) were recorded daily during the experiment to ascertain Temperature humidity index (THI) value. THI was calculated as per NRC (1971). THI of winter (49.67±1.18), spring (64.65±0.41), and summer (87.28±1.26) obtained from ICAR-CSSRI, Karnal were the three subclasses of THI considered in association analysis.
THI = 0.72 (Wb + Db) + 40.6
Where, Wb is wet bulb temperature and Db is dry bulb temperature in °C.
The denominators 23 and 38.33 in the equation represent the normal RR and RT (°C) of cattle, respectively, under ideal conditions.
Rectal Temperature (RT) and Respiration Rate (RR)
RR of each animal was recorded by visual observation of inward and outward flank movement. RT was recorded in centigrade with a digital thermometer by keeping the thermometer in contact with rectal mucosa for about 2 minutes. RR and RT were recorded at 6-8 am, 12-02 pm, and 12-02 pm during winter (January), spring (March) and summer (June) respectively. Recording of each of the parameters was done in each of the three seasons at the probable extreme hours of day. Heat tolerance coefficient (HTC) was calculated by Benezra Coefficient of Heat Adaptability (Benezra, 1954) with the following formula-
HTC= RR/23 + RT/38.33
The experimental data obtained from three seasons (summer, spring and winter) have been subjected to standard methods of statistical analysis. The mean values and standard deviations (Mean ±SD) were calculated and the analysis was performed using General Linear Methods (GLM) procedure of statistical analysis system.
Results and Discussions
The ambient temperature (Ta), temperature-humidity index (THI) and relative humidity (RH) during the experimental period are shown in Table 1.
Table 1: Ambient temperature (°C), temperature-humidity index (THI) and RH during which physiological parameters were recorded
|T ºC Max||17.23±.67||26.43±1.53||39.35±0.94|
The data indicate that the highest mean value of Ta (39.35±0.94°C) was measured in summer (May) while the minimum mean value was recorded during winter (January). The minimum mean value of RH (31±0.57%) was measured in May (summer), whereas higher value (98.5±1.5%) was recorded in January (winter). Temperature humidity index (THI) considered being the scale for measuring the heat stress on animals was calculated at different season (Table 1). Abdelatif and Alameen (2012) reported the THI value of crossbred dairy cows (Holstein-Friesian X Zebu) under tropical conditions during summer (80.92) induced high heat stress whereas the value during winter (65.75) is considered to be comfortable to dairy cows. Singh et al., 2014 reported that the duration and intensity of Tmax and THI (>72) has adverse effects on different breeds of cattle and buffaloes depending upon their adaptability to tropical climatic conditions. They found that the THI value during summer (87.28±1.26) was markedly higher compared to the value obtained in winter (49.67±1.18). A sudden change (rise or fall) in maximum or minimum temperature during summer and winter season negatively affect the normal physiology, growth, milk production and reproduction of cattle and buffaloes (Singh and Upadhyay, 2008).
The rectal temperature is recognized as an important measure of physiological status as well as the ideal indicator for assessment of heat storage in animal’s body (Koga et al., 2004). Analysis of variance (ANOVA) of linear model for dependent variable RT in Sahiwal and Karan Fries cows was found to be highly significant at 1% level of significance. RT differed significantly in all three seasons (Table 2 and Table 3) in both Sahiwal and Karan Fries cows. In Sahiwal cows RT (°C) during winter, spring and summer were 37.300±0.095c, 38.178±0.095b and 38.810±0.095arespectively, whereas RT (°C) in Karan Fries were 37.492±0.115c, 38.398±0.115b and 39.186±0.115a during winter, spring and summer respectively. The magnitude of increase in RT were significantly (P<0.05) higher during summer compared to winter and spring season (Table 2 and 3).
Table 2: Mean ± SE of Physiological Parameters of Sahiwal Cows during Different Seasons
|Season||Respiration Rate (Breaths min-1)||Rectal Temperature (°C)||Heat Tolerance Coefficient (HTC)|
Table 3: Mean ± SE of Physiological Parameters of Karan Fries Cows during Different Seasons
|Season||Respiration Rate (Breaths min-1)||Rectal Temperature (°C)||Heat Tolerance Coefficient (HTC)|
The results of present investigation are in accordance to Singh and Upadhyay, (2009) who reported the positive relationship of temperature rise and increase in RT in Sahiwal and Karan Fries cows. Kadzere et al., 2002 reported that the body temperature of dairy cattle shows great susceptibility to thermal load and it is considered as a sensitive indicator of thermal stress. Chandra Bhan et al., 2013, reported positive correlation between RT, humidity and other physiological responses in Murrah buffaloes and Karan-Fries cattle. Several other reports (Koubkova et al., 2002; Chakravarthi et al., 2004; Singh and Singh, 2005; Chandra Bhan et al., 2012) also indicated similar observations of higher rectal temperature in animals exposed to higher ambient temperature. In addition, several studies have shown that the basal metabolic rate of zebu cattle is generally lower compared to Bos taurus (Hansen, 2004; Srikandakumar and Johnson 2004; Gaughan et al., 2010). Therefore, low producing dairy animal exhibits an increased heat tolerance (Reid et al., 1991).
Analysis of variance (ANOVA) of linear model for dependent variable RR in Sahiwal and Karan Fries cows was found to be highly significant at 1% level of significance. RR differed significantly in all three seasons (Table 2 and Table 3) in both Sahiwal and Karan Fries cows. In Sahiwal cows RR (breaths min-1) during winter, spring and summer were 15.738±0.795c, 18.158±0.795b and 29.818±0.795a respectively, whereas RR in Karan Fries during winter, spring and summer were 15.779±1.136c, 22.979±1.136b and 47.299±1.136a respectively. This observed pattern of RR revealed that with increase in THI there was increase in RR in both Sahiwal and Karan Fries cows. The results of present investigation are in accordance to Das et al., 1999, Singh and Singh (2005), Singh and Upadhyay (2009) who observed higher respiration rate with an increase in ambient temperature and relative humidity. Chandra Bhan et al., 2012 reported increased respiration rate of growing and adult Sahiwal cattle during summer as compared to spring season. Several other reports (Gaughan et al., 2000; Bouraoui et al., 2002; Mayengbam et al., 2008) also indicated similar observations of higher respiration rate in animals exposed to higher ambient temperature. Increased in RR was also reported in growing and adult buffaloes during afternoon compared to forenoon due to exposure (Vaidya et al., 2010; Singh et al., 2014) Similarly, Kumar et al., 2009 also found lower respiration (11 breaths min-1) in lactating buffaloes kept under cooling system (fan cum mist system) compared to their counterpart kept under natural climatic conditions. However, increased respiration is an important thermoregulatory response to heat stress. It aids dissipation of excess body heat by vaporizing more moisture in the expired air (Beatty et al., 2006). Hence, lower RR indicates an improved thermotolerance.
Heat Tolerance Coefficient
Heat tolerance coefficient was calculated by Benezra Coefficient of Heat Adaptability formula (BCA) (Benezra, 1954). Analysis of variance (ANOVA) of linear model for dependent variable HTC in Sahiwal and Karan Fries cows was found to be highly significant at 1% level of significance. HTC differed significantly in all three seasons in both Sahiwal and Karan Fries cows. HTC of Sahiwal cows in winter, spring and summer were 1.657±0.035c, 1.785±0.035b and2.308±0.035a whereas HTC of Karan Fries were 1.628±0.036c, 1.756±0.036b and 2.280±0.036arespectively (Table 2 and 3). The observed value revealed that Sahiwal has a better thermoregulatory mechanism than Karan Fries cows. Mandal and Tyagi (2008) reported that the thermal adaptability of Holstein Friesian and Sahiwal crossbred bulls was highest during the winter season followed by summer and rainy. Das, (2012) also reported that HTC was significantly lower (1.884 ± 0.045) during the month of December in crossbred calves (Holstein Friesian x Indigenous Local) indicating highest adaptability of calves in winter (December). Therefore, HTC may help to rank individual animals in respect of adaptability to existing environmental condition.
The present study revealed that the magnitude of increase in RR, RT and HTC were higher during summer compared to other seasons in both Sahiwal and Karan Fries cows. It was observed that Sahiwal cows are less sensitive and better able to regulate thermoregulatory mechanism in response to high environmental temperature than Karan Fries cows, which may be due to their long time adaptation with tropical climates, low metabolic rate and great sweating capacity. Therefore, development and adoption of procedures viz. managerial, nutritional and genetic may help to reduced impact of thermal stress that effect the reproductive and productive efficiency in high-yielding dairy cows and the health status of animals living in hot environments.
The authors gratefully acknowledge Director, NDRI, Karnal and Head, DCB Division, NDRI, Karnal for providing facilities to carry out the research work. Financial support provided by NICRA project is enormously acknowledged.