Meteorological data
Temperature humidity index (THI) was calculated using the following formula of
Johnson (1963) in both summer and winter. The results of the THI in both summer and winter are given in Table 1. Significant difference (p<0.05) was evident in minimum, maximum and mean THI of both the seasons. High environmental temperature has adverse effects on the physiological functions of dairy animals and affects their productivity (
Polsky and von Keyserlingk, 2017). This can further be aggravated when it is accompanied by high humidity
(Collier et al., 2017). To measure the intensity of environmental stress, THI has been developed (
Alhussien and Dang, 2018). It is one of the best methods to evaluate heat stress in animals (
Marai and Haeeb, 2010). The THI is a result of the combined effect of temperature and relative humidity (
Dikmen and Hansen, 2009) which determine the microclimatic conditions of the animal. When the THI reaches 72, cows change their behaviour
(Kamal et al., 2018; Herbut and Angrecka, 2018), yield and composition of milk gets altered
(Liu et al., 2017). Based on the THI index,
(Helal et al., 2010) a THI of 74 or less considered as normal, 75-78 alert, 79-83 danger and 84 and above an emergency. THI values more than 72 stressful, while THI above 78 indicated severe heat stress to buffaloes (
Payne, 1990). THI values higher than 80 units have been classified as danger zone to the well-being and productivity of cattle
(Segnalini et al., 2013). In the present study, animals calving in winter were found to be within the thermo comfort zone, while those calving in summer were under danger condition with a very high THI, this indicated that the animals were under severe heat stress. The buffaloes were more affected by heat stress compared to cows which indicate that buffaloes are more prone to stress due to high environmental variables
(Hady et al., 2018). The high susceptibility of buffaloes to thermal stress ; could be attributed to low potentiality to dissipate heat from the body surface due to fewer sweat glands and black colored skin.
Haematological parameters
The haematological parameters were used to assess the physiological homeostasis of the animals
Abd Ellah et al., (2013). The results of the effect of season and transition on haematological parameters were presented in Table 2 and 3. In winter, no significant difference (p>0.05) was observed in TEC, TLC, Hb, monocyte %, PCV, MCV, MCH, MCHC among all the weeks of transition period as well control (p>0.05). In summer, no significant difference (p>0.05) was observed in TEC, TLC, monocyte %, PCV, MCV, MCH, MCHC among all the weeks of transition period as well control (p>0.05). The Mean ± SE of the TEC in two weeks prepartum, day zero and control were significantly higher (p<0.05) in summer compared to winter. In the present study, transition period did not affect the TEC significantly in the seasons studied. Similar findings were reported earlier in buffaloes (
Abdulkareem, 2013 and
Abdelrazek et al. 2018); cattle (
Hadj et al. 2015); sheep (
El-Ebissy, 2011); goat (
Daramola et al.2004). In winter, no significant difference in Hb was observed among all the weeks of transition period as well in control, while in summer, the Hb concentration was significantly lower (p<0.05) in 1 week prepartum compared to 2 weeks prepartum and control. The Hb concentration was significantly higher (p<0.05) in 2 weeks prepartum compared to 1 week prepartum, 2
nd and 3
rd weeks postpartum. Also no significant difference in Hb concentration from one week prepartum to 3
rd week postpartum was observed. No change in TEC and Hb during transition period in the present may be attributed to similar threshold of stress throughout the transition period (
Vasantha et al. 2020).
The TEC values in 2 weeks of prepartum, day zero and control were significantly higher (p<0.05) in summer compared to winter. This effect could be attributed to increased levels of cortisol during summer which enhance erythroid progenitor proliferation and positively influence erythropoiesis
(Voorhees et al., 2013). During summer, to alleviate heat stress, cutaneous blood flow increases to dissipate heat. Increased cutaneous vascular flow up-regulates intracutaneous erythropoietin production that in turn contributes to the increased erythropoietin plasma levels (Ralf
Paus et al., 2009). Increased erythrocyte count and haemoglobin concentration in the blood during summer compared to winter could be ascribed to increased erythropoietin that in addition to conferring protection to tissues also stimulated erythropoiesis.
In the present study, the TLC in all the weeks of transition period and control did not differ significantly in between summer and winter. In support to the present findings
Aengwanich et al. (2011) in cattle and
Hassan et al., (2013) in goats also reported the same. The lack of significant difference between the seasons under study might be attributed to the adaptation of the species to the increasing THI during summer season
(Hassan et al., 2013).
The Mean ± SE of the Hb in all the weeks of transition period and control were significantly higher (p<0.05) in summer compared to winter. Similar findings in cattle were reported in the studies of
Shrikande et al. (2008) and
AL-Saeed (2009). In contrary to our results, significantly decreased Hb was noticed in summer compared to winter in cattle (
Kumar and Pachauri, 2000;
Al-Saeed et al. (2009) and
Mirzadeh et al., 2010).
The PCV in all the stages of transition period and control had no significant difference (p>0.05) in both the seasons. Similar to our findings
Nikhil et al., (2018) reported that season had no effect on haematological parameters such as Hb, PCV, MCV, MCH, MCHC while TEC was significantly lower in monsoon compared to pre and post monsoon seasons in cross bred calves.
Abdelrazek et al., (2018) revealed non-significant (p>0.05) changes in TEC, PCV, Hb, MCV, MCH, MCHC along transition period during postpartum period in buffaloes.
The MCV values on two weeks prepartum, day zero and control were significantly higher (p<0.05) in winter compared to summer. The MCH levels in one week and third week postpartum samples were significantly higher (p<0.05) in summer compared to winter. The Mean ± SE of the MCHC in all the weeks of transition period and control were significantly higher (p<0.05) in summer compared to winter. The variation in MCV might be due to physiological adaptation of the animals or that indices like MCV might not have been affected by heat stress. The increased MCHC in our study during summer could be attributed to increased erythropoiesis. The sampling interval, methodology used for the experiment, numbers of animals sampled and/or degree of metabolic disturbances might be contributing factors that brought about variation in results of certain haematological parameters observed in our study (
Hadj et al. 2015). Also, the non-significant difference observed in few of the stages of transition period and in between the seasons might also be attributed to variation in individual level of physiological adaptation of the animals.
Biochemical parameters
The results of the effect of season and transition on biochemical parameters were presented in Table 4. In winter, the SOD levels on two weeks postpartum, were significantly higher (p<0.05) than two weeks prepartum, day zero and one week postpartum. The SOD levels on one week postpartum was significantly lower (p<0.05) compared to one week prepartum, two week, three week postpartum and control. In summer, the SOD levels in two weeks prepartum, one week prepartum were significantly higher (p<0.05) compared to other weeks and control. The SOD levels in transitional and control buffaloes were significantly higher (p<0.05) in summer than winter. Similar to our results of SOD in winter,
Agarwal et al., (2012) evidenced decreased erythrocytic SOD activity in transition period, towards calving and the value further declined after parturition. The findings of
Singh et al., (2017) were similar to our results, with a significant decrease in levels of SOD throughout the transition period. The reason behind the decreased SOD activity, around calving may be due to altered homeostatic control
(Agarwal et al., 2012). Usually proxidants and antioxidants are in equal concentrations maintaining the oxidative balance, under stressful conditions the system tries to combat oxidative stress by elevating the concentrations of antioxidant enzymes such as SOD, GPx and catalase, Whereas under extreme stressful ambience the antioxidant system fails to combat pro-oxidants resulting in oxidative stress which is usually termed as altered hemostasis.
Kumar et al. (2011) also similarly observed significantly (p<0.05) increased erythrocyte SOD activity in buffaloes exposed to hot dry and hot humid conditions in a climate chamber. As the calving approached, the reserves of the antioxidant defence gets exhausted due to excessive lipolysis induced by persistently high cortisol levels and thereby excess generation of free radicals
(Hady et al., 2018). Hence parturition combined with seasonal stress significantly decreased the SOD levels to the day of calving which indicated that the combined effect was more pronounced on the day of calving.
The GSH levels on day zero of parturition was significantly lower (p<0.05) compared to other weeks of transition period and control in both the seasons.
Sharma et al., (2011) and
Singh et al., (2017) also reported decreased GSH concentration in early lactation compared to advanced pregnancy. The GSH levels on day zero, one week postpartum and control were found to be significantly higher (p<0.05) in winter than summer. The present results were contrary to the findings of
Kumar et al., (2007) and
Kumar et al. (2011) in buffaloes. It implied that production of GSH from GSSH (oxidized glutathione) was more prior to parturition and less after parturition. The higher levels of GSH in summer compared to winter could be due to involvement of GSH dependent enzymes glutathione peroxidase and glutathione reductase to control oxidative stress leading to intense regeneration of GSH from GSSH obtained after reduction of peroxides into alcohols
(Kizil et al., 2007). The variations in GSH reported in our study was attributed to age, breed, timing and frequency of sampling, nutrition, environment, analytical procedures adopted to measure and management practices (
Castillo et al. 2006).
The MDA concentration on day zero of parturition was significantly higher (p<0.05) when compared to other weeks of transition period and control in both the seasons. The MDA concentration in transition and control buffaloes except in the three weeks postpartum were significantly higher (p<0.05) in summer compared to winter. The findings of
Abdelrazek et al., (2018) and
Hady et al., (2018) were similar to ours with significant increase in MDA postpartum compared to late gestation. Significantly higher levels of MDA on day zero of parturition reflected the increased oxidative stress in the animals. The decreasing trend in MDA during the post transition period might be due to the gradual adaptation of the animal’s body to the metabolic alterations leading to the animal regaining homeorhesis
(Abuelo et al., 2015). The MDA levels in all the different weeks of transition period except in the three weeks postpartum were significantly higher (p<0.05) in summer compared to winter. In line with our results,
Kumar et al., (2011) reported increased TBARS in adult buffaloes in both hot dry and hot humid conditions induced in a climate chamber. The animals in our study initially during the prepartum stage efficiently overcame the stress with increased levels of SOD, GSH and with less MDA formed. However, at parturition, the free radicals might have increased, anti oxidant reserves decreased (reduced SOD, GSH levels) and increased lipid peroxides (increased MDA concentration). During the postpartum period the animals were relieved from stress as indicated by the decreased MDA concentration.