Temperature Humidity Index (THI) at the start of trial (1
st week of July) averaged 82.96±0.51 which decreased non-significantly during July, August month until 5
th week of experiment thereafter THI increased up to 7
th week of trial which is shown below in Table 1.
Clinico-physiological parameters
The changes clinico-physiological parameters are depicted in Table 2, the clinico-physiological parameters like respiration rate, heart rate, rectal temperature in Group 1 showed elevated pattern.
Liu et al. (2019) also found elevated pattern in these physiological parameters in heat stressed animals but our findings are in non-significant pattern, probably cause may be shorter time period for exposure to increased ambient environment temperature and also ad-lib availability of water supply. Also, there was no significant difference of rectal temperature, heart rate, respiration rate in the post-treatment values in Group 2 and 3 as compared to Group 1 animals. The respiration rate in Group 2 animals showed decreased inclination within and also than Group 1 and Group 3 animals, probably is due to the osmo-regulatory effect of betaine which helped to offset the hyperthermia.
Hassan et al. (2011) also found significant changes in respiration rate of betaine supplemented rabbit group as compared to the control group.
The dairy animals during the present study were not exposed to that much high ambient temperature and this might be the possible cause for the non-significant changes in all the groups with respect to heart rate, rectal temperature.
An Qiang et al. (2009) also reported same changes in heart rate, rectal temperature in Cr supplemented group as compared to control group.
Haematological changes seen during study
The haemoglobin and PCV values in Group 1 animals showed decreased inclination when compared with normal values post heat stress as stated in Table 3.
El-Nouty et al. (1990) reported same changes and the cause is haemo-dilution effect in heat stressed dairy cattle, because more water is transported inside vasculature which is due to RBC lysis either by increased attack of free radicals on its membrane or insufficient nutrient availability for Hb synthesis as the animal consumes less feed or decreases voluntary intake upon increased ambient temperature.
In Group 2 and Group 3 (Table 3) animals there is decreased Hb and PCV levels followed by spike in same values but as non-significant change. Same change has been seen by the
Moonsie-Shageer and Mowat (1993) after Cr supplementation in stressed feeder calves where as possible cause for the same in Group 3 might be due to the anti-oxidants in the mineral mixture which provided substrate directly or indirectly for the various scavenging enzymes
e.g., Mg is used in the phosphorylation of various components of enzyme system.
Regarding the leukocyte derangement in heat stressed dairy cattle we found only significant increase of neutrophils and decrease in lymphocyte and eosinophils with the increase in THI pattern in Group 1 animals (Table 3). Our results are in accordance with
Peek and Divers (2008) who found stress and glucocorticoids reliably alter the leukogram to create neutrophilia, lymphopenia and eosinopenia. Other likely cause for lymphopenia is the result of an immediate shift of lymphocytes from the circulating blood to other tissues, but the specific location is unknown. Other than this heat stress leads to increased secretion of glucocorticoid hormone which can induce apoptosis of lymphoid cells in mammals as stated by
Schwartzman and Cidlowski (1994) while as neutrophilia might be due to a relative shift of neutrophils into circulating blood most likely contributing to this change.
The mitigation of heat stress in Group 2 and Group 3 using chromium as main micronutrient supplementation and copper and Manganese as main mineral supplements in mixture respectively has aided to reverse the changes in leucogram caused by heat stress (Table 3).
Burton et al. (1993) also found improved lymphocyte proliferation in Cr supplemented calves and increased immune-stimulatory effects thereby ameliorating the stress leukogram which can be correlated with the decrease in the cortisol concentration. As the heat stress causes increased oxidative stress which has negative effects on leukogram, Cu and Mn are integral parts of blood antioxidant oxide dismutase, when these metals are supplied through feed in sufficient quantities, suitable antioxidant enzymes are produced in the body which ameliorate the effect of oxidative stress and thereby stress leukogram.
Changes in milk parameters after heat stress and its amelioration
In Group 1 animals there is decrease in the milk production with the increase in the THI as shown in Table 4. Previous workers like
Al Reyad et al. (2016) reported significant decrease in milk production and significant changes in milk composition during hot ambient temperature. The cause for the decrease in milk yield might be due to a reduction in DMI which decreases the nutrients accessible for milk synthesis.
In our study the THI happened to be between moderate ranges which can be one possible cause for on-specific changes in the milk constituents despite decrease in milk production with the change in THI.
Al-Saiady et al. (2004) investigated effect of chelated chromium effect on the milk yield and milk composition in Holstein cows under thermal stress. The increased milk yield can possibly be described by higher dry matter intake (DMI) and proficiency of energy utilization by Cr supplementation. In our present study same effect has been seen in Group 2 animals (Table 4) with significant change in milk yield after supplementation with chromium when compared with the ongoing increase in THI.
In Group 3 animals there is positive effect on milk yield post heat stress but the changes were not significantly remarked (p<0.05) which makes our findings contrary to the
West et al. (1991) who found feeding diets that have a high dietary cation-anion difference (DCAD) improved DMI and milk yield, our results are probably such due to the short period for supplementation of minerals under hot ambient temperature.
Changes in biochemical values with respect to increased THI
In Group 1 animals there is increased cortisol concentration due to positive effect of increased ambient temperature on hormone secretion (Table 5) and this is in agreement with
Aggarwal and Upadhyay, (2013). Concurrently, the cortisol concentration in Group 2 animals decreased significantly with the mitigation by micro-nutrient chromium supplementation and betaine supplementation,
Chang and Mowat (1992) and
Moonsie-Shageer and Mowat (1993);
Anne-Marie et al. (2012);
Alirezaei et al. (2014) also found decreased serum cortisol concentration in Cr methionine and wheat bran supplemented group calves. Besides this in Group 3 animals, cortisol concentration was decreased post supplementation with the increased THI values due to the effect of the minerals which play an important role in immune status of animal and help in combating negative effects of free radical generation by providing substrate for production of suitable antioxidant enzymes which ameliorate the effect of stress. Same findings have been reported by
Aggarwal and Upadhyay, (2013).
Blood glucose Group 2 animals decreased significantly as compared to the Group 1 animals (Table 5). Our findings are in consonance with the findings of
Vincent (2000). The decreased blood glucose may be due to increased potency of insulin to its receptors by chromium. Similar changes in glucose level has been reported by
Chang et al. (1996) who observed lower serum glucose concentration in chromium nicotinate supplemented group.
Same change has been seen in Group 3 animals with the increasing THI and our findings are in agreement with
Aggarwal and Upadhyay, (2013) who suggested Cu and Mn play an important role in immune system and carbohydrate and lipid metabolism thereby fading the effect of stress hormone cortisol which has positive correlation with glucose.
High environmental temperature cause decrease in total plasma protein in lactating cattle which was seen in our study at peak THI values in Group 1 (Table 5),
Podar and Oroian (2003) also found same results in lactating cattle. In Group 2 animals there is increased total protein concentration over increasing THI which I supported by
Huang et al. 2006 who also found betaine supplementation (0.125% to finishing 25 pigs) increased serum basal concentrations of total protein by 9%. The decrease in protein in both the groups might be partly due to the utilization of protein in cell repair and tissue organization with the formation of lipoproteins which are important cellular constituents.
Sodium level, potassium level, chloride levels of Group 2 and Group 3 animals increased as compared to Group 1 animals (Table 5) and were in accordance with findings of
Maltz et al. 1994.
Moeckel et al. (2002) studied the effect of betaine and suggested betaine inhibits the activity of Ca
2+ and Na
+/K+ ion pumps by 73 and 64%, respectively. Thus, it can be assumed that the accumulation of betaine in intestinal tissues might control water movement by decreasing the activity of water pumps in Group 2 animals. Moreover, the calcium levels also increased in Group 2 and Group 3 animals as compared to stressed ones which is supported by the findings of
Moonsie-Shageer and Mowat (1993).
Plasma Cr (ppb) in Group 2 animals increased as compared to Group 1 animals and our results are in agreement with
Spears (1999). Supplementation of Cr resulted in dose-dependent linear increase in tissue Cr concentration which is in agreement with the study conducted by
Spears (1999).
Liver enzymes ALT and AST in Group 2 animals decreased as compared to Group 1 animals which is in agreement with
Nazifi et al. 2003 who found similar results in fat tailed sheep during high ambient temperature. The increase in the serum enzymes is probably due to the fact that enzymes are surrounded by cellular membrane, so they could not easily get across cellular membrane into blood in normal condition. But extreme condition, such as heat stress could change the cellular membrane permeability, so enzyme activity increased when animals were under heat stress which is in agreement with
Li et al. (2001).
Sahin et al. (2002a, b, 2005) reported chromium picolinate supplementation (CrPic) linearly decreased serum corticosterone concentration which is possible cause for decrease in membrane degradation.
Status of metalloenzymes and their amelioration
Metalloenzymes which include superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase in Group 2 animals and Group3 animals showed significant change as compared to Group 1 animals (Table 6). Our Study is in consonance with
Anne-Marie et al. (2012) that chromium may act as an indirect antioxidant by decreasing high levels of insulin and preventing auto-oxidation of glucose.
Bhat et al. (2008) also reported decreased levels of metalloenzymes due high atmospheric temperature and humidity of summer which increases neuroendocrine stress and lipid peroxidation which in turn contributes to the reduced erythrocyte antioxidant response which was seen in Group 1 animals in our study. As already mentioned in the preceding sections heat stress causes increased oxidative stress and Cu and Mn being integral parts of blood antioxidants, when these metals are supplied through feed in sufficient quantities, suitable antioxidant enzymes are produced in the body which ameliorate the effect of oxidative stress which can be seen in the values of Group 3 animals.
