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Full Research Article

Effect of Temperature-Humidity Index and Dietary Energy on Growth and Feed Efficiency in Pigs

P
P.K. Pathak1
R
R. Roychoudhury2
J
J. Saharia3
M
M.C. Borah4
D
D.J. Dutta5
R
R. Bhuyan6
S
S. Borah7,*
A
A.K. Mohanty8
1Senior Scientist, ICAR-ATARI, Zone VI, Umiam-793 103, Meghalay, India.
2College of Veterinary Science, Assam Veterinary and Fishery University, Khanapara-781 022, Guwahati, India.
3Department of Livestock Production Management, College of Veterinary Science, Assam Veterinary and Fishery University, Khanapara-781 022, Guwahati, India.
4Department of Veterinary Physiology, College of Veterinary Science, Assam Veterinary and Fishery University, Khanapara-781 022, Guwahati, India.
5Department of Animal Nutrition, College of Veterinary Science, Assam Veterinary and Fishery University, Khanapara-781 022, Guwahati, India.
6Department of Animal Nutrition, College of Veterinary Science, Assam Veterinary and Fishery University, Khanapara, Guwahati-781 022, Asaam, India.
7Department of Veterinary Physiology and Biochemistry, Lakhimpur College of Veterinary Science, Assam Veterinary and Fishery University, Joyhing-787 051, Assam, India.
8Director, ICAR-ATARI, Zone VI, Umiam-793 103, Meghalaya, India.

ABSTRACT

Background: Pig rearing is well imbibed in the people of north eastern states of India and offers a source of income to rural tribal masses. However, change in climatic parameters especially the increase in temperature due to global warming causes significant production losses thereby affecting the poor farmers.

Methods: Two genetic groups, Hampshire and Hampshire × Local, were studied in this agro-climatic study in Assam State, India, to determine the influence of temperature stress on productive metrics. Two distinct seasons of the year were used to measure the pigs’ cortisol levels. Thermal stress in the experimental animals was measured using the Temperature Humidity Index (THI). 

Result: During summer (79.55 - 82.56) both the groups showed higher (P<0.01)  concentration of serum cortisol compared to the winter season. The THI was found to negatively affect the food conversion efficiency , body weight gain and linear body measurements in both the genetic groups. Subsequently, to overcome the effect of THI, different feed formulations varying in energy content were fed to the pigs during summer and winter season.  The diet contained 3260, 2936.5 and 3585.8 kcal/kg of metabolisable energy in the grower ration and 3260.2, 2936.6 and 3587 kcal/kg in the finisher ration for the normal energy (NE), low energy (LE) and high energy (HE) rations, respectively.  The results indicated that the energy level included in the diet had a significant impact on the body weight gain (P<0.01) and reduced the average daily body weight gain during the summer time.  Incorporating HE resulted in a decrease in feed intake and an increase in FCE. Data showed that the growth performance of pigs in Assam varied with the season. Although reduced feed intake during the summer season was a major limiting factor to growth rate. Modification of diet with increasing the energy density might be helpful to minimize the production losses due to thermal stress.

INTRODUCTION

Pig rearing is a traditional practice In India and source of income especially for tribal folks of the country. There are 9.06 million pigs in India (20th Livestock Census, 2019, Govt. of India) which has decreased by 12.06% over previous livestock census (19th Livestock Census, 2012. In India, pigs comprise 1.7% of the total livestock population, which contribute about 6.7% of the total meat production in the country (Mohakud et al., 2020, Naskar et al., 2015). The North-Eastern region of India comprises of eight states with 3.9 million pigs, which contributes to about 28.23% of the total pig population of the country (20th Livestock Census, 2019 Govt. of India). The region has an agrarian society with more than 59 per cent tribal population who are mostly non-vegetarian in their dietary habit and pork is the major source of animal protein.
       
The Assam state in the North Eastern region of India falls in a zone that experiences hot and humid climatic conditions with high rainfall, especially during the summer and hence, the livestock in this part of the country suffers from harmful effects of thermal stress. Pigs have a thick layer of subcutaneous fat covering their bodies, which significantly slows heat escape and they lack functional sweat glands in their skin, making them more susceptible to high environmental temperatures than other livestock species (Krider and Carrol, 1967; Borah et al., 2012).  Pigs rely mostly on panting to dissipate heat due to their insufficient sweat glands (Patience et al., 2005), particularly in situations when they lack access to a wallowing place. Therefore, it is a need of the hour to identify the climate resilient improved pig breeds or genetic groups and to develop appropriate ameliorative measures to reduce the detrimental effects of heat stress for optimum production.   
       
So far, no comprehensive study has been carried out in this aspect in the climatic conditions of Assam. Hence, the present study was formulated to find out the  effect of climatic variabiles on feed intake, linear body measurements and growth performance of different genetic group of pigs under the climatic conditions of North Eastern region of India. Further- more to study the amelioratory effect of  different level of energy ration in variation of stress hormone level in pigs.

MATERIALS AND METHODS

Study area
 
The study area is located in the North Eastern region of India between 21o57' and 29o30'N latitude and 89o2' and 97o24'E longitude. The plain area of this region is characterized by hot and very humid climate with high rainfall during the summer season. The present experiment was conducted in the Assam state of India in the institutional pig farm and the laboratory work was conducted in the Department of Veterinary Physiology, College of Veterinary Science, Assam Agricultural University, Khanapara, Assam, India.  
 
Data collection
 
In the experiment, a total of 18 weaned (56 days of age) piglets with similar  body weight (10.55±0.12 kg) from each of the two genetic groups (Hampshire and Hampshire ×  Local) irrespective of sex were randomly selected. The experiment was conducted in two phases; during the winter months (October to March; first phase) and summer months (April to September; second phase) to find out the effect of season related climatic variability on feed intake, linear body measurements and growth performance of different genetic group of pigs. 
       
A total of three rations were prepared for grower and finisher pigs (NRC, 1998). The rations with 110 kcal/kg Metaboliseable Energy, 100 kcal/kg Metaboliseable Energy and 90% kcal/kg Metaboliseable Energy as per NRC (1998) designated as high energy (HE), normal energy (NE) and low energy (LE), respectively. The ingredients and composition of experimental rations has been given in Table 1. The supplemented energy level of NE, LE and HE in the treatment indicated three groups of pigs’ viz. Gr.I (Control animals), Gr.II and Gr.III, respectively for both the season.  The Gr.I was reared as a control group for both the seasons. The experimental animals were fed grower feed till attainment of 35 kg body weight and thereafter, the finisher ration was fed up to the end of the trial. The rations were attuned along with the change in live weight at fortnightly intervals. All standard managemental practices were adopted during the study period along with experimental pigs had free access to clean drinking water. 

Table 1: Percentage composition of experimental ration.


       
In two distinct seasons, the average monthly temperature of the interior and outdoor environments as well as the relative humidity (RH) were measured at 8.30 a.m. and 5.30 p.m.  The THI was calculated using the ambient temperature and relative humidity (RH) data and the formula from Mader and Kreikemeier (2006) is shown below:
 
THI= (0.8 × Tdb) + [(RH/100) × (Tdb - 14.4)] + 46.4
 
Serum cortisol levels were measured using the Radioimmunoassay (RIA) technique and were thought to be a sign for temperature stress. At 15-day intervals during the experiment, serum samples were aseptically taken from each experimental animal.
       
The experimental pigs were weighed in the morning hours before feeding at fortnightly interval. A measured quantity of specific ration was offered to experimental pigs in the morning at 9.30 am and in the evening at 3.30 pm and the left over was collected and weighed to calculate the feed conversion efficiency by quantity of feed consumed (kg)/ body weight gain (kg). 
 
Data analysis
 
The data recorded during the experimental period were presented using descriptive statistics like mean and standard error (SE). Multi factor analysis of variance technique was used for comparing different factors like season, treatment, genetic group and shed difference. Linear mathematical model was considered for the purpose. The pictorial presentation was also made for comprehensive understanding. For analysis of data SAS 9.3 (English) licensing up to July 30, 2017 was used. 

RESULTS AND DISCUSSION

The study revealed that in the morning, outdoor THI was (P<0.01) higher than indoor THI, whereas, there was no significant difference between the indoor and outdoor THI during evening hours both in winter and in summer season (Table 2). A higher (P<0.01) THI was recorded in the evening of both winter (73.31-73.81) and summer (82.26-82.56) season. The present experiment showed that the average THI ranged from 79.55 to 82.56 during summer and 67.21 to 73.81 during winter season. 

Table 2: Average diurnal variation of indoor and outdoor temperature humidity index (THI) during winter and summer.


       
Serum cortisol levels in all three treatment groups varied (P<0.01) during the winter (108.89-110.33 nmol/l) and summer (185.60–236.75 nmol/l) seasons (Fig 1).  However, no significant differences were found between the two genetic groupings.  While there was no discernible difference between the treatment groups in the winter, in the summer, Gr. III pigs had a lower (P<0.01) cortisol concentration (185.60 nmol/l) than the other treatment groups, which included both Hampshire and Hampshire x Local pigs.

Fig 1: Serum cortisol (nmol/l) concentrations of Hampshire and Hampshire ´ Local pigs in the different treatment groups.


       
The results of the analysis of variance revealed that Hampshire and Hampshire x Local pigs grew more body weight in the winter than in the summer (P<0.01) and that Hampshire pigs gained more body weight than Hampshire × Local pigs (Table 3).  Additionally, statistical data analysis showed that the pigs’ body weight gain was influenced (P<0.01) by the energy content of their meal.

Table 3: Average total gain in body weight (kg) of Hampshire and Hampshire × local pigs in the different treatment groups.


       
Linear body measurements showed no significant difference between the summer and winter seasons in terms of daily changes in height and body length at withers; however, all treatment groups except Grade III showed greater (P<0.01) daily changes in heart girth during the winter. In comparison to Hampshire × Local pigs, Hampshire pigs showed greater daily variations in body length, heart girth and height at withers and there was a significant (P<0.01) difference between the two genetic groups (Table 4, 5 and 6).  The average daily changes in body length, heart circumference and height at the withers were larger (P<0.01) in Grade III, followed by Grade I and Grade II, according to the analysis of variance.

Table 4: Average daily changes in body length (cm) of Hampshire and Hampshire × local pigs in the different treatment groups.



Table 5: Average daily changes in heart girth (cm) of Hampshire and Hampshire × local pigs in the different treatment groups.



Table 6: Average daily changes in height at withers (cm) of Hampshire and Hampshire × local in the different treatment groups.


       
According to the current study, the average total feed intake was higher (P<0.01) in the winter than in the summer (Fig 2). The study also found that Hampshire pigs consumed more feed than Hampshire × Local pigs (P<0.05).  Statistical data demonstrated that the feed consumption was influenced (P<0.05) by the diet’s energy content.  According to the FCR data collected for the study, the winter season had a higher (P<0.05) FCR than the summer.  Additionally, the Hampshire x Local pigs had a higher FCR (P<0.05) than the Hampshire pigs (Table 7).  The Gr. III animals had a better (P<0.01) FCR, according to dietary energy fluctuation.

​

Fig 2: Average total feed intake (kg) of Hampshire and Hampshire × Local pigs in different treatment groups.



Table 7: Feed conversion ratio (FCR) of Hampshire and Hampshire × local pigs in the different treatment groups.


   
Pigs have a dense layer of subcutaneous fat covering their bodies, which prevents heat from escaping and they lack functional sweat glands in their epidermis, making them more susceptible to high ambient temperatures.  According to Chakraborty and colleagues (Chakraborty, 2017), the northeastern Indian states were previously largely immune to heat stress in comparison to the rest of the country. However, as a result of climate change and global warming, these states are now also experiencing high summer temperatures, which causes heat stress in livestock and varying degrees of production losses.  The current results are consistent with a previous study (Nass, 2006) that found that a THI of less than 75 is normal for pigs, while a THI of 75 to 78 indicates that the animals are likely to be experiencing heat stress and a THI of 79 to 83 indicates that the animals would be seriously impacted.  When THI exceeds 83, the animal becomes extremely stressed and may eventually perish.  According to Davis and Madder (2002), THI is a dependable tool for managing livestock effectively in a variety of climatic conditions and an appropriate climatic marker to correlate climatic stress on animal physiology and productivity.  According to the current study, the average THI for pigs throughout the summer was higher than their comfort level and falls within the danger zone.
       
Serum cortisol concentration  is used as the physiological marker to identify the stresses in animals (Aggarwal and Singh, 2010). Heat stress exposure in animals activates the hypothalamo-pituitary-adrenal axis (Abilay et al., 1975), making the estimation of hormone concentrations, particularly cortisol, a significant indicator for assessing heat stress in these animals. The current investigation found that summertime serum cortisol concentrations were noticeably greater than wintertime levels. The study also reveals non-significantly higher concentration of cortisol in Hampshire pigs than the Hampshire × Local pigs during summers. This might be due to more vulnerability of Hampshire pigs to summer stress. In present study, it could be observed that there was no significant difference between the treatment groups during winter season but during the summer season, significantly (P<0.01) higher cortisol level was recorded in Gr.II (LE) followed by Gr.I (NE) and Gr.III (HE). Sejian et al. (2010) also reported significant increase in serum cortisol concentration in Malpura ewes exposed to thermal and nutritional stress. But they found reduction of cortisol level in nutritionally stressed ewes. This is indicative of differential adaptive capacity of the animals.  From the study it was observed that lower level of cortisol in Gr.III (HE) than Gr.I (NE) and Gr.II (LE) might be due to the effect of increasing the concentration of dietary energy through the incorporation of vegetable fat (5%) which might reduce the heat increment of the diet and thus allow pigs to become more heat tolerant (Velayudhan et al., 2015).
       
The significant effect of thermal stress during summer season on body weight gain of pigs in the present study was in agreement with the findings of Das et al., (2001). Pigs generally attempt to reduce the impacts of summer heat stress in two main ways since they are homeostatic animals.  These include a decrease in heat generated by bodily metabolism and an improvement in heat dissipation.  Pigs will expand their body surface area by sprawling out to make more contact with a cool surface, such as a floor.  Pigs will also raise their respiration rate (RR) in order to dissipate more heat.  By consuming less feed, the pig can lower its metabolic heat output since heat is produced during the eating, digestion and nutrient absorption processes (the heat increment of feeding).  In order to reduce the heat increase caused by feeding and, consequently, the quantity of heat that must be released into the environment, the pig voluntarily reduces the amount of feed that it consumes (Velayudhan et al., 2015).  A reduction in feed intake results in reduced growth which affects the body weight gain and this might be the primary reason of significantly (P<0.01) lower average daily body weight gain in summer season than the winter season.
       
In the present study, it was found that Hampshire breed gained  higher (P<0.01) average daily body weight than Hampshire x Local pigs, but it was further observed that Hampshire pigs comparatively gain less average daily body weight in summer than the winter season as compared to Hampshire x Local pigs. This might be due to the less tolerance of Hampshire pigs to thermal stress (THI >75) during summer season, as the recorded THI ranged from 79.55±0.28 to 84.20±0.30 in inside the sty. The findings support earlier observations of Thornton et al., (2009). 
       
Animals utilise dietary energy for maintenance and productive performance.  Basal metabolism and involuntary processes including muscle tone, feed digestion, blood circulation and tissue renewal are also considered maintenance functions (Verstegen et al., 1987).  After maintenance energy needs are met, the pig can focus its energy on developing lean and fatty body tissues and increase in size. Furthermore, metabolisable energy is used to meet the pig’s various energy needs, including growth, maintenance, protein or lipid gain, milk production, etc. (Noblet et al., 1994a).  A significant difference in the average efficiency of ME utilisation for these several functions has been shown in the past: roughly 80% for fat accumulation or maintenance, 60% for protein deposition, 75% for weight gain during growth and 70% for milk (Noblet et al., 1994a).  According to Sirohi and Michaelowa, (2007), our research further supports earlier results that livestock may experience heat stress due to hot and muggy weather, which can result in behavioural and metabolic changes, such as decreased feed intake and a drop in production. Changing the energy levels of the feed formulation could help overcome this lower production (Sailo, 2011), which is what we attempted in our study as well.  The average daily body weight gain in Gr. III (HE) was then found to have decreased the least amount in the summer compared to the winter when 10% more energy (NRC, 1998 recommendation) was added to the diet in the form of vegetable oil.  This could be attributed to nutritional adjustments that reduce the influence of a hot and humid environment on swine development performance throughout the summer season.  These results are consistent with previous studies by Velayudhan et al., (2015).
       
In the present study, daily changes in body length and height at withers had no significant difference between winter and summer season but recorded higher value during winter than summer season in all experimental groups. In case of heart girth, analysis of variance revealed (P<0.01) higher measurement in winter in all experimental groups except Gr.III (HE) in both the genetic groups. It was observed that Hampshire pigs had (P<0.01) higher measurement of body length, heart girth and height at withers than the Hampshire x Local pigs which was in accordance with the findings of Dash and Mishra (1986). A significant (P<0.01) effect of dietary energy levels (Table 4, 5 and 6) on the average daily changes in the linear body measurements of the present study might be attributed to the higher growth rate of pigs that were fed with HE ration as compared to the LE ration. The higher daily changes in body length; heart girth and height at withers of pigs fed with HE diets had been well documented by Sailo (2011). However, in contrast to the present finding, Das (2000) had reported non-significant effect of dietary energy levels on the body measurements.
       
Exposure to high ambient temperature has been shown to affect daily feed intake (Black et al., 1993; McGlone, 1999) which finally results in lower body weights. The average total feed intake was higher (P<0.01) during winter season than the summer season which might be due to the lower THI during winter season providing thermal comfort to the animals. The less intake of feed during summer season might be an effort of animal to lower heat increment due to feed metabolism which was in agreement with the findings of (Velayudhan et al., 2015). Although the average total feed intake was significantly (P<0.01) higher in Hampshire pigs, a significantly (P<0.01) lower feed intake could be seen in high energy incorporated group (Gr.III) as compared to the others which may be attributed to the increase energy density of the diet.
       
The recorded better (P<0.01) FCR value during winter as compared to summer season might be due to the favourable environmental temperature during winter (THI: 67.21 to 73.81) that helped to maintained feed intake and body metabolism (Mayer and Bucklin, 2001). According to Tokach et al., (2010), the HE integrated group had a reduced feed intake and a superior (P<0.01) FCR when there was dietary energy-wise variation. This could be because the Gr. III group’s feed was energy-rich and deficient in fibre.

CONCLUSION

The recorded average THI during summer season (79.55 - 82.56) was above the comfort zone and it lies in the danger zone (79 - 83) for pigs in Assam. In the present study, significantly higher cortisol concentration was recorded in summer in ME and LE group. However, during summer lower cortisol concentration was recorded in HE incorporated group. Study also indicated that the  addition of dietary energy cold significantly (P<0.01) influence on the body weight gain through ameolorating the thermal stresses in pigs.  Body length, heart girth and height at withers with the body weight of Hampshire and Hampshire × Local pigs was found to be positively correlated and it was recorded that linear body measurements of pig were in progressively increasing trend along with increase in body weight. The Hampshire × Local pigs showed the highest FCR during the winter.  Lower feed intake and better FCR were noted in the HE-incorporated group when there was dietary energy-wise variation.  According to the current study, dietary energy is essential for reducing thermal stress in pigs living in hot, humid areas like the northeastern Indian states.  Additional research in this area will support the growth of the pig business in these states.

ACKNOWLEDGEMENT

The author’s are thankful to the authority of institutional pig farm, Dept. of Animal Nutrition,  Dept. of Veterinary Physiology and Dept. of Livestock Production and Management, College of Veterinary Science, Assam Agricultural University, Khanapara, Guwahati for necessary help to undertaking the research works.
 
Statement of animal rights
 
The Institutional Animal Ethics Committee of the College of Veterinary Science, Assam Agricultural University, Khanapara, Guwahati 781022, gave its approval to the current study.

CONFLICT OF INTEREST

No conflicts of interest are disclosed by the writers.

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    Full Research Article

    Effect of Temperature-Humidity Index and Dietary Energy on Growth and Feed Efficiency in Pigs

    P
    P.K. Pathak1
    R
    R. Roychoudhury2
    J
    J. Saharia3
    M
    M.C. Borah4
    D
    D.J. Dutta5
    R
    R. Bhuyan6
    S
    S. Borah7,*
    A
    A.K. Mohanty8
    1Senior Scientist, ICAR-ATARI, Zone VI, Umiam-793 103, Meghalay, India.
    2College of Veterinary Science, Assam Veterinary and Fishery University, Khanapara-781 022, Guwahati, India.
    3Department of Livestock Production Management, College of Veterinary Science, Assam Veterinary and Fishery University, Khanapara-781 022, Guwahati, India.
    4Department of Veterinary Physiology, College of Veterinary Science, Assam Veterinary and Fishery University, Khanapara-781 022, Guwahati, India.
    5Department of Animal Nutrition, College of Veterinary Science, Assam Veterinary and Fishery University, Khanapara-781 022, Guwahati, India.
    6Department of Animal Nutrition, College of Veterinary Science, Assam Veterinary and Fishery University, Khanapara, Guwahati-781 022, Asaam, India.
    7Department of Veterinary Physiology and Biochemistry, Lakhimpur College of Veterinary Science, Assam Veterinary and Fishery University, Joyhing-787 051, Assam, India.
    8Director, ICAR-ATARI, Zone VI, Umiam-793 103, Meghalaya, India.

    ABSTRACT

    Background: Pig rearing is well imbibed in the people of north eastern states of India and offers a source of income to rural tribal masses. However, change in climatic parameters especially the increase in temperature due to global warming causes significant production losses thereby affecting the poor farmers.

    Methods: Two genetic groups, Hampshire and Hampshire × Local, were studied in this agro-climatic study in Assam State, India, to determine the influence of temperature stress on productive metrics. Two distinct seasons of the year were used to measure the pigs’ cortisol levels. Thermal stress in the experimental animals was measured using the Temperature Humidity Index (THI). 

    Result: During summer (79.55 - 82.56) both the groups showed higher (P<0.01)  concentration of serum cortisol compared to the winter season. The THI was found to negatively affect the food conversion efficiency , body weight gain and linear body measurements in both the genetic groups. Subsequently, to overcome the effect of THI, different feed formulations varying in energy content were fed to the pigs during summer and winter season.  The diet contained 3260, 2936.5 and 3585.8 kcal/kg of metabolisable energy in the grower ration and 3260.2, 2936.6 and 3587 kcal/kg in the finisher ration for the normal energy (NE), low energy (LE) and high energy (HE) rations, respectively.  The results indicated that the energy level included in the diet had a significant impact on the body weight gain (P<0.01) and reduced the average daily body weight gain during the summer time.  Incorporating HE resulted in a decrease in feed intake and an increase in FCE. Data showed that the growth performance of pigs in Assam varied with the season. Although reduced feed intake during the summer season was a major limiting factor to growth rate. Modification of diet with increasing the energy density might be helpful to minimize the production losses due to thermal stress.

    INTRODUCTION

    Pig rearing is a traditional practice In India and source of income especially for tribal folks of the country. There are 9.06 million pigs in India (20th Livestock Census, 2019, Govt. of India) which has decreased by 12.06% over previous livestock census (19th Livestock Census, 2012. In India, pigs comprise 1.7% of the total livestock population, which contribute about 6.7% of the total meat production in the country (Mohakud et al., 2020, Naskar et al., 2015). The North-Eastern region of India comprises of eight states with 3.9 million pigs, which contributes to about 28.23% of the total pig population of the country (20th Livestock Census, 2019 Govt. of India). The region has an agrarian society with more than 59 per cent tribal population who are mostly non-vegetarian in their dietary habit and pork is the major source of animal protein.
           
    The Assam state in the North Eastern region of India falls in a zone that experiences hot and humid climatic conditions with high rainfall, especially during the summer and hence, the livestock in this part of the country suffers from harmful effects of thermal stress. Pigs have a thick layer of subcutaneous fat covering their bodies, which significantly slows heat escape and they lack functional sweat glands in their skin, making them more susceptible to high environmental temperatures than other livestock species (Krider and Carrol, 1967; Borah et al., 2012).  Pigs rely mostly on panting to dissipate heat due to their insufficient sweat glands (Patience et al., 2005), particularly in situations when they lack access to a wallowing place. Therefore, it is a need of the hour to identify the climate resilient improved pig breeds or genetic groups and to develop appropriate ameliorative measures to reduce the detrimental effects of heat stress for optimum production.   
           
    So far, no comprehensive study has been carried out in this aspect in the climatic conditions of Assam. Hence, the present study was formulated to find out the  effect of climatic variabiles on feed intake, linear body measurements and growth performance of different genetic group of pigs under the climatic conditions of North Eastern region of India. Further- more to study the amelioratory effect of  different level of energy ration in variation of stress hormone level in pigs.

    MATERIALS AND METHODS

    Study area
     
    The study area is located in the North Eastern region of India between 21o57' and 29o30'N latitude and 89o2' and 97o24'E longitude. The plain area of this region is characterized by hot and very humid climate with high rainfall during the summer season. The present experiment was conducted in the Assam state of India in the institutional pig farm and the laboratory work was conducted in the Department of Veterinary Physiology, College of Veterinary Science, Assam Agricultural University, Khanapara, Assam, India.  
     
    Data collection
     
    In the experiment, a total of 18 weaned (56 days of age) piglets with similar  body weight (10.55±0.12 kg) from each of the two genetic groups (Hampshire and Hampshire ×  Local) irrespective of sex were randomly selected. The experiment was conducted in two phases; during the winter months (October to March; first phase) and summer months (April to September; second phase) to find out the effect of season related climatic variability on feed intake, linear body measurements and growth performance of different genetic group of pigs. 
           
    A total of three rations were prepared for grower and finisher pigs (NRC, 1998). The rations with 110 kcal/kg Metaboliseable Energy, 100 kcal/kg Metaboliseable Energy and 90% kcal/kg Metaboliseable Energy as per NRC (1998) designated as high energy (HE), normal energy (NE) and low energy (LE), respectively. The ingredients and composition of experimental rations has been given in Table 1. The supplemented energy level of NE, LE and HE in the treatment indicated three groups of pigs’ viz. Gr.I (Control animals), Gr.II and Gr.III, respectively for both the season.  The Gr.I was reared as a control group for both the seasons. The experimental animals were fed grower feed till attainment of 35 kg body weight and thereafter, the finisher ration was fed up to the end of the trial. The rations were attuned along with the change in live weight at fortnightly intervals. All standard managemental practices were adopted during the study period along with experimental pigs had free access to clean drinking water. 

    Table 1: Percentage composition of experimental ration.


           
    In two distinct seasons, the average monthly temperature of the interior and outdoor environments as well as the relative humidity (RH) were measured at 8.30 a.m. and 5.30 p.m.  The THI was calculated using the ambient temperature and relative humidity (RH) data and the formula from Mader and Kreikemeier (2006) is shown below:
     
    THI= (0.8 × Tdb) + [(RH/100) × (Tdb - 14.4)] + 46.4
     
    Serum cortisol levels were measured using the Radioimmunoassay (RIA) technique and were thought to be a sign for temperature stress. At 15-day intervals during the experiment, serum samples were aseptically taken from each experimental animal.
           
    The experimental pigs were weighed in the morning hours before feeding at fortnightly interval. A measured quantity of specific ration was offered to experimental pigs in the morning at 9.30 am and in the evening at 3.30 pm and the left over was collected and weighed to calculate the feed conversion efficiency by quantity of feed consumed (kg)/ body weight gain (kg). 
     
    Data analysis
     
    The data recorded during the experimental period were presented using descriptive statistics like mean and standard error (SE). Multi factor analysis of variance technique was used for comparing different factors like season, treatment, genetic group and shed difference. Linear mathematical model was considered for the purpose. The pictorial presentation was also made for comprehensive understanding. For analysis of data SAS 9.3 (English) licensing up to July 30, 2017 was used. 

    RESULTS AND DISCUSSION

    The study revealed that in the morning, outdoor THI was (P<0.01) higher than indoor THI, whereas, there was no significant difference between the indoor and outdoor THI during evening hours both in winter and in summer season (Table 2). A higher (P<0.01) THI was recorded in the evening of both winter (73.31-73.81) and summer (82.26-82.56) season. The present experiment showed that the average THI ranged from 79.55 to 82.56 during summer and 67.21 to 73.81 during winter season. 

    Table 2: Average diurnal variation of indoor and outdoor temperature humidity index (THI) during winter and summer.


           
    Serum cortisol levels in all three treatment groups varied (P<0.01) during the winter (108.89-110.33 nmol/l) and summer (185.60–236.75 nmol/l) seasons (Fig 1).  However, no significant differences were found between the two genetic groupings.  While there was no discernible difference between the treatment groups in the winter, in the summer, Gr. III pigs had a lower (P<0.01) cortisol concentration (185.60 nmol/l) than the other treatment groups, which included both Hampshire and Hampshire x Local pigs.

    Fig 1: Serum cortisol (nmol/l) concentrations of Hampshire and Hampshire ´ Local pigs in the different treatment groups.


           
    The results of the analysis of variance revealed that Hampshire and Hampshire x Local pigs grew more body weight in the winter than in the summer (P<0.01) and that Hampshire pigs gained more body weight than Hampshire × Local pigs (Table 3).  Additionally, statistical data analysis showed that the pigs’ body weight gain was influenced (P<0.01) by the energy content of their meal.

    Table 3: Average total gain in body weight (kg) of Hampshire and Hampshire × local pigs in the different treatment groups.


           
    Linear body measurements showed no significant difference between the summer and winter seasons in terms of daily changes in height and body length at withers; however, all treatment groups except Grade III showed greater (P<0.01) daily changes in heart girth during the winter. In comparison to Hampshire × Local pigs, Hampshire pigs showed greater daily variations in body length, heart girth and height at withers and there was a significant (P<0.01) difference between the two genetic groups (Table 4, 5 and 6).  The average daily changes in body length, heart circumference and height at the withers were larger (P<0.01) in Grade III, followed by Grade I and Grade II, according to the analysis of variance.

    Table 4: Average daily changes in body length (cm) of Hampshire and Hampshire × local pigs in the different treatment groups.



    Table 5: Average daily changes in heart girth (cm) of Hampshire and Hampshire × local pigs in the different treatment groups.



    Table 6: Average daily changes in height at withers (cm) of Hampshire and Hampshire × local in the different treatment groups.


           
    According to the current study, the average total feed intake was higher (P<0.01) in the winter than in the summer (Fig 2). The study also found that Hampshire pigs consumed more feed than Hampshire × Local pigs (P<0.05).  Statistical data demonstrated that the feed consumption was influenced (P<0.05) by the diet’s energy content.  According to the FCR data collected for the study, the winter season had a higher (P<0.05) FCR than the summer.  Additionally, the Hampshire x Local pigs had a higher FCR (P<0.05) than the Hampshire pigs (Table 7).  The Gr. III animals had a better (P<0.01) FCR, according to dietary energy fluctuation.

    ​

    Fig 2: Average total feed intake (kg) of Hampshire and Hampshire × Local pigs in different treatment groups.



    Table 7: Feed conversion ratio (FCR) of Hampshire and Hampshire × local pigs in the different treatment groups.


       
    Pigs have a dense layer of subcutaneous fat covering their bodies, which prevents heat from escaping and they lack functional sweat glands in their epidermis, making them more susceptible to high ambient temperatures.  According to Chakraborty and colleagues (Chakraborty, 2017), the northeastern Indian states were previously largely immune to heat stress in comparison to the rest of the country. However, as a result of climate change and global warming, these states are now also experiencing high summer temperatures, which causes heat stress in livestock and varying degrees of production losses.  The current results are consistent with a previous study (Nass, 2006) that found that a THI of less than 75 is normal for pigs, while a THI of 75 to 78 indicates that the animals are likely to be experiencing heat stress and a THI of 79 to 83 indicates that the animals would be seriously impacted.  When THI exceeds 83, the animal becomes extremely stressed and may eventually perish.  According to Davis and Madder (2002), THI is a dependable tool for managing livestock effectively in a variety of climatic conditions and an appropriate climatic marker to correlate climatic stress on animal physiology and productivity.  According to the current study, the average THI for pigs throughout the summer was higher than their comfort level and falls within the danger zone.
           
    Serum cortisol concentration  is used as the physiological marker to identify the stresses in animals (Aggarwal and Singh, 2010). Heat stress exposure in animals activates the hypothalamo-pituitary-adrenal axis (Abilay et al., 1975), making the estimation of hormone concentrations, particularly cortisol, a significant indicator for assessing heat stress in these animals. The current investigation found that summertime serum cortisol concentrations were noticeably greater than wintertime levels. The study also reveals non-significantly higher concentration of cortisol in Hampshire pigs than the Hampshire × Local pigs during summers. This might be due to more vulnerability of Hampshire pigs to summer stress. In present study, it could be observed that there was no significant difference between the treatment groups during winter season but during the summer season, significantly (P<0.01) higher cortisol level was recorded in Gr.II (LE) followed by Gr.I (NE) and Gr.III (HE). Sejian et al. (2010) also reported significant increase in serum cortisol concentration in Malpura ewes exposed to thermal and nutritional stress. But they found reduction of cortisol level in nutritionally stressed ewes. This is indicative of differential adaptive capacity of the animals.  From the study it was observed that lower level of cortisol in Gr.III (HE) than Gr.I (NE) and Gr.II (LE) might be due to the effect of increasing the concentration of dietary energy through the incorporation of vegetable fat (5%) which might reduce the heat increment of the diet and thus allow pigs to become more heat tolerant (Velayudhan et al., 2015).
           
    The significant effect of thermal stress during summer season on body weight gain of pigs in the present study was in agreement with the findings of Das et al., (2001). Pigs generally attempt to reduce the impacts of summer heat stress in two main ways since they are homeostatic animals.  These include a decrease in heat generated by bodily metabolism and an improvement in heat dissipation.  Pigs will expand their body surface area by sprawling out to make more contact with a cool surface, such as a floor.  Pigs will also raise their respiration rate (RR) in order to dissipate more heat.  By consuming less feed, the pig can lower its metabolic heat output since heat is produced during the eating, digestion and nutrient absorption processes (the heat increment of feeding).  In order to reduce the heat increase caused by feeding and, consequently, the quantity of heat that must be released into the environment, the pig voluntarily reduces the amount of feed that it consumes (Velayudhan et al., 2015).  A reduction in feed intake results in reduced growth which affects the body weight gain and this might be the primary reason of significantly (P<0.01) lower average daily body weight gain in summer season than the winter season.
           
    In the present study, it was found that Hampshire breed gained  higher (P<0.01) average daily body weight than Hampshire x Local pigs, but it was further observed that Hampshire pigs comparatively gain less average daily body weight in summer than the winter season as compared to Hampshire x Local pigs. This might be due to the less tolerance of Hampshire pigs to thermal stress (THI >75) during summer season, as the recorded THI ranged from 79.55±0.28 to 84.20±0.30 in inside the sty. The findings support earlier observations of Thornton et al., (2009). 
           
    Animals utilise dietary energy for maintenance and productive performance.  Basal metabolism and involuntary processes including muscle tone, feed digestion, blood circulation and tissue renewal are also considered maintenance functions (Verstegen et al., 1987).  After maintenance energy needs are met, the pig can focus its energy on developing lean and fatty body tissues and increase in size. Furthermore, metabolisable energy is used to meet the pig’s various energy needs, including growth, maintenance, protein or lipid gain, milk production, etc. (Noblet et al., 1994a).  A significant difference in the average efficiency of ME utilisation for these several functions has been shown in the past: roughly 80% for fat accumulation or maintenance, 60% for protein deposition, 75% for weight gain during growth and 70% for milk (Noblet et al., 1994a).  According to Sirohi and Michaelowa, (2007), our research further supports earlier results that livestock may experience heat stress due to hot and muggy weather, which can result in behavioural and metabolic changes, such as decreased feed intake and a drop in production. Changing the energy levels of the feed formulation could help overcome this lower production (Sailo, 2011), which is what we attempted in our study as well.  The average daily body weight gain in Gr. III (HE) was then found to have decreased the least amount in the summer compared to the winter when 10% more energy (NRC, 1998 recommendation) was added to the diet in the form of vegetable oil.  This could be attributed to nutritional adjustments that reduce the influence of a hot and humid environment on swine development performance throughout the summer season.  These results are consistent with previous studies by Velayudhan et al., (2015).
           
    In the present study, daily changes in body length and height at withers had no significant difference between winter and summer season but recorded higher value during winter than summer season in all experimental groups. In case of heart girth, analysis of variance revealed (P<0.01) higher measurement in winter in all experimental groups except Gr.III (HE) in both the genetic groups. It was observed that Hampshire pigs had (P<0.01) higher measurement of body length, heart girth and height at withers than the Hampshire x Local pigs which was in accordance with the findings of Dash and Mishra (1986). A significant (P<0.01) effect of dietary energy levels (Table 4, 5 and 6) on the average daily changes in the linear body measurements of the present study might be attributed to the higher growth rate of pigs that were fed with HE ration as compared to the LE ration. The higher daily changes in body length; heart girth and height at withers of pigs fed with HE diets had been well documented by Sailo (2011). However, in contrast to the present finding, Das (2000) had reported non-significant effect of dietary energy levels on the body measurements.
           
    Exposure to high ambient temperature has been shown to affect daily feed intake (Black et al., 1993; McGlone, 1999) which finally results in lower body weights. The average total feed intake was higher (P<0.01) during winter season than the summer season which might be due to the lower THI during winter season providing thermal comfort to the animals. The less intake of feed during summer season might be an effort of animal to lower heat increment due to feed metabolism which was in agreement with the findings of (Velayudhan et al., 2015). Although the average total feed intake was significantly (P<0.01) higher in Hampshire pigs, a significantly (P<0.01) lower feed intake could be seen in high energy incorporated group (Gr.III) as compared to the others which may be attributed to the increase energy density of the diet.
           
    The recorded better (P<0.01) FCR value during winter as compared to summer season might be due to the favourable environmental temperature during winter (THI: 67.21 to 73.81) that helped to maintained feed intake and body metabolism (Mayer and Bucklin, 2001). According to Tokach et al., (2010), the HE integrated group had a reduced feed intake and a superior (P<0.01) FCR when there was dietary energy-wise variation. This could be because the Gr. III group’s feed was energy-rich and deficient in fibre.

    CONCLUSION

    The recorded average THI during summer season (79.55 - 82.56) was above the comfort zone and it lies in the danger zone (79 - 83) for pigs in Assam. In the present study, significantly higher cortisol concentration was recorded in summer in ME and LE group. However, during summer lower cortisol concentration was recorded in HE incorporated group. Study also indicated that the  addition of dietary energy cold significantly (P<0.01) influence on the body weight gain through ameolorating the thermal stresses in pigs.  Body length, heart girth and height at withers with the body weight of Hampshire and Hampshire × Local pigs was found to be positively correlated and it was recorded that linear body measurements of pig were in progressively increasing trend along with increase in body weight. The Hampshire × Local pigs showed the highest FCR during the winter.  Lower feed intake and better FCR were noted in the HE-incorporated group when there was dietary energy-wise variation.  According to the current study, dietary energy is essential for reducing thermal stress in pigs living in hot, humid areas like the northeastern Indian states.  Additional research in this area will support the growth of the pig business in these states.

    ACKNOWLEDGEMENT

    The author’s are thankful to the authority of institutional pig farm, Dept. of Animal Nutrition,  Dept. of Veterinary Physiology and Dept. of Livestock Production and Management, College of Veterinary Science, Assam Agricultural University, Khanapara, Guwahati for necessary help to undertaking the research works.
     
    Statement of animal rights
     
    The Institutional Animal Ethics Committee of the College of Veterinary Science, Assam Agricultural University, Khanapara, Guwahati 781022, gave its approval to the current study.

    CONFLICT OF INTEREST

    No conflicts of interest are disclosed by the writers.

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