The present investigation was carried out on twelve numbers of Indian zebu cattle of 2 years of age. The study aimed to see the variation in certain stress related hormones and LDH enzyme of zebu cattle in summer and winter seasons of Assam. The select stress related hormones such as cortisol, T3 and T4 were estimated by RIA technique and the enzyme i.e. LDH (lactate dehydrogenase) activity was estimated by using commercially available kit. The results showed that there was a significant (P<0.01) difference in the estimated hormones and LDH concentration between the summer and winter seasons. The significant change in hormone concentration and enzyme activity in summer might be attributed to the adaptation of the animals towards the changing climate.
Heat stress caused by a combination of ambient temperature, relative humidity, low wind velocity and solar radiation increases body physiological characters and can reduce feed intake and milk production (Hahn, 1999; West, 2003). The variation in climatic variables like temperature, humidity and radiations were recognized as the potential hazards in the growth and production of all livestock species. The degree of environmental impact is modified by stage of the animal’s life cycle and adaptation of the breed and species. A high environmental temperature clearly reduces the milk yield of a cow which is due to reduced feed intake and extra energy being utilized to combat heat stress. A decline of 8 percent in milk yield was found in summer season when the mean afternoon temperature was 39.8 °C compared with winter season (Folman et al., 1979). One of the recent economic studies has suggested severe losses if the current management systems are not changed as a result of climate change (Nardone et al., 2010). Therefore, there is great need of attention in understanding how domestic animals respond to climate stressors. Heat stress is one of the major influencing factors to reduce animal reproduction and productivity. With thermal discomfort, the animal seeks ways to lose heat by means of a sequence of adaptation devices involving respiratory, circulatory, excretory, endocrine and nervous systems. Compositely, the adaptation characteristics can determine the tolerance of each breed to their environment, which can be estimated from the enzymatic traits (McManus et al., 2009). Coordination of all these systems is required in order to maintain the productive potential under thermal stress irrespective of species, breeds and individuals. Changes that induce thermal imbalance include a combination of several environmental factors namely, sunlight, thermal radiation, humidity, air temperature and thermo-regulatory mechanisms (St-Pierre et al., 2003). Further, the endocrine glands such as adrenal and thyroid glands respond quickly to bring the necessary physiological adjustments in animals to the changing environmental conditions. Hence, the biochemical homeostasis is of prime importance to counteract heat stress and therefore, need scientific approach to surface out various unknown fact. The animals of this region used to experience on slot of summer heat stress because this region of our country suffer from some detrimental effect of thermal stress as most of the time the state (Assam) remains under high tropical and extra-tropical air masses. Moreover, most of the time the state remains under tropical high heat and humid dominance which causes many detrimental effects in the animals of this region due to the effect of thermal stress. Assam is having high humidity during summer season where the THI (Temperature Humidity Index) goes above 80 while the other three seasons are comfortable with THI ranging between 55-70 (approx) (Saikia, 2015). Therefore, the present study was formulated to examine the changes in certain stress related hormones and LDH (Lactate Dehydrogenase) enzyme concentrations in indigenous zebu cattle which may results due to the change in seasons so as to take necessary managemental steps in the stressful periods.
Materials and Methods
The protocol of this experiment was approved by Institutional Animal Ethics Committee of Assam Agricultural University, Khanapara, Guwahati, Assam.
Experimental Period and Selection of Animal
The experiment was conducted in the two seasons i.e. summer (June to August) and winter (December to February). Twelve numbers of female Indian zebu cattle of age 2 years were selected such that they were free from any anatomical and reproductive disabilities and diseases. They were maintained under semi-intensive system in the Experimental Animal Shed, Department of Veterinary Physiology, C.V. Sc. Khanapara, A.A.U., Guwahati-22, Assam, India with latitude and longitude position being 26o 10’ N and 91o 44’ E respectively. The physiological parameters such as the rectal temperature and respiration rate were examined by conventional methods to examine the general health of the animals during the whole experimental period. They were supplied with both green fodder and concentrate as per the standard feeding practices of the farm.
Calculation of Temperature Humidity Index (THI)
The aforesaid necessary meteorological data i.e. dry bulb temperature and relative humidity were recorded daily for the whole experimental period from the Automatic Weather Station (AWS) installed at the Experimental Animal Shed, Department of Veterinary Physiology, C.V. Sc., Khanapara, AAU, Guwahati-22, Assam, India. The temperature-humidity index (THI) was calculated for the entire period of study using the following formula as per Mader et al., 2006.
THI= (0.8 × Tdb) + [(RH/100) × (Tdb-14.4)] +46.4
Where, THI- temperature humidity index, Tdb- temperature dry bulb, RH- relative humidity.
Collection of Blood Sample
The venous blood was collected from jugular vein aseptically from each of the experimental animals fortnightly for the whole experimental period. The collected blood sample was transferred into clean and autoclaved centrifuge tube and allowed to clot in slanting position and then the tubes were subjected to centrifugation at 2000 g for 15 minutes to separate out serum which was then used for the analysis of the select hormones and lactate dehydrogenase enzyme.
Estimation of Select Hormones
The level of certain thermal stress related serum hormones such as tri-iodothyronine (T3), thyroxine (T4) and cortisol were estimated by Radio immuno-assay (RIA) technique using RIA kits supplied by Immunotech, Czech Republic. The tracer, I-125 was used in the estimation technique, which involved competition between free and isotope tagged hormones for binding to the limited antibody sites and subsequently quantification was made through calibration curve. The estimation used 6 well Automatic Gamma counter procured from Stratec W. Germany. The intra and inter assay co-efficient of variation were found to be 6.3 percent and 7.7 percent for triiodothyronine, 6.2 percent and 8.6 percent for thyroxine and 5.8 percent and 9.2 percent for cortisol. The results obtained in the assay were expressed in nmol/L.
Estimation of Lactate Dehydrogenase (LDH)
Lactate dehydrogenase enzyme activity was estimated by using the commercial kit manufactured by Greiner Diagnostic GmbH, Unter Gereuth 10-D-79353, Bahlingen-Germany.
The data obtained were statistically analyzed (Snedecor and Cochran, 1994).
The different the serum hormones and LDH enzyme observed in the zebu cattle in summer and winter seasons are presented in the Table 1. The mean THI were recorded as 67.86 and 83.7 during the winter and hot humid summer seasons respectively. The rectal temperature and respiration rate of all the animals were found to be within the physiological range. The mean serum cortisol concentration of zebu cattle in the summer season was significantly (P<0.01) higher than the winter season. On the contrary, the mean serum tri-iodothyronine (T3) and thyroxine (T4) concentration was higher in the winter compared to the summer season and this difference was highly significantly (P<0.01) respectively. Similarly, the mean LDH enzyme concentration was recorded as higher significantly (P<0.01) in the summer compared to the winter season.
Table 1: Mean± SE of the select hormones and LDH enzyme concentration in zebu cattle in summer (June to July) and winter (December to February) season
|Attributes||Winter Season (December to February)||Summer Season
(June to July)
|Cortisol Hormone (nmol/L)||25.92a±0.24||40.39b±0.32|
|T3 Hormone (nmol/L)||1.08a±0.03||0.85b±0.03|
|T4 Hormone (nmol/L)||40.05a±0.37||33.88b ±0.45|
|LDH Enzyme (U/L)||105.08a±0.22||196.15b±0.31|
ab means bearing the different superscript within a parameter in a row differ significantly (p<0.01)
The serum cortisol concentration was found to be significantly differed between the summers and winter season (Table 1). Cortisol played an important role in the different types of stress in animals and therefore, it was considered as a good stress marker in animals (Yates et al., 2008; Aggarwal and Singh, 2010). It had been reported that there were various stressors that were responsible to activate hypothalamo-pituitary-adrenal axis in domestic farm animals which resulted in increase cortisol level and subsequently caused increase in plasma glucocorticoides concentration (Abilay et al., 1975; Minton, 1994). That might be the reason of increase cortisol concentration in summer season in order to tolerate the climatic stressful conditions. It had been observed that the plasma cortisol level increased during acute heat stress and decreased during the chronic phase (Marai and Habeeb, 2010). In addition, previous researchers observed that glucocorticoids functioned as vasodilators and facilitated heat loss, which had stimulatory effect on proteolysis and lipolysis and thereby, providing energy to the animal (Cunningham, 2007).
The serum thyroid hormones (T3 and T4) were observed to be highly significant (P<0.01) between the two seasons (Table 1). The previous researchers reported that blood thyroid hormones were good indicators of metabolic status of an animal (Magdub et al., 1982; Todini et al., 2009). So, based on the metabolic or physiological status of the animals, the concentration of thyroid hormones varied. As such, season, breed and age of the animals had a significant effect on plasma concentration of 3-3’-5-triiodothyronine (T3) and thyroxine (T4). Our findings were similar to the previous researchers (Bhattacharyya et al., 1995; Dutta et al., 2002; Bhooshan et al., 2010). The decrease in thyroid hormone concentration in the summer might be attributed to the high ambient temperature that can markedly suppressed thyroid hormone levels due to lower feed intake (Folman et al., 1979). Johnson, 1980 reported that a decline in the plasma concentration of T3 from 2.2 to 1.16 ng/ml in thermal exposed lactating cows and they also observed that heat production and body temperature regulation were effectively controlled by thyroid gland. In addition, acute heat exposure induced decrease in plasma T3 and T4concentration in young and old buffalo calves (Nessim, 2004) and Friesian calves (Yousef et al., 1997). Increase in secretion of thyroid hormone increases the metabolism and hence heat production. Therefore, decreased thyroid hormone levels during heat stress are an adaptive response and also might be an attempt to reduce the metabolic rate and heat production (West et al., 1999; Riis and Madsen, 1985). Moreover, when the animals start to suffer due to heat in summer season, their food ingestion is reduced and thereby, metabolism slows down, causing a hypo-function of the thyroid gland (McManus et al., 2009). There was a significant (P<0.01) difference in serum LDH enzyme concentration between the summer and winter season (Table 1). The mean plasma values of LDH ranged from 202.43±18.97 to 505.27±24.70 IU/L in adult Karan Fries cattle during the different season (Bhan et al., 2013). Similarly, significantly higher LDH level in native Patanwadi sheep and its crosses with Merino and Rambouillet was reported when the sheep were exposed to direct sunlight from 32.3°C to 38.7°C for 3 consecutive days (Patel et al., 1991). Our findings were corroborated to those of the previous researchers who reported a significantly different LDH concentration among the seasons (Bhan et al., 2013). Therefore, increased LDH enzyme activity during the summer season might be due to an increase muscular activity involve in cellular respiration through catalization by which pyruvate from glucose was converted into usable energy as lactate in the cells. Moreover, when animals were subjected to heat stress, it causes damage or injury to the animal tissues which might result in increase LDH level and thus LDH get released into the bloodstream (Joseph et al., 2002).
The present study revealed that there was an increase in the production of certain serum variables like cortisol, T3, T4 and LDH enzyme in zebu cattle. All the estimated serum hormones and the LDH enzyme in zebu cattle were found to be significantly (P<0.01) higher in the summer compared to the winter season. This increased concentration in the studied variables might help the animals to adapt and acclimatize themselves to the changing environmental condition in summer season. Hence, it is concluded that the significant increase in select serum hormones and LDH enzyme in zebu cattle in the summer season might help the farmers and the animal breeders of this region to alter the managemental conditions for effective production strategies.