MSc.

The production of crossbred dairy cattle is adversely affected by the thermal stress, specifically in hot humid states as that of Kerala. Thus the assessment of stress intensity and its correlation with physiological alterations are of profound significance in laying down appropriate mitigation strategies specifically when thermal stress induces oxidative stress in the late gestation period. Hence this study is formulated to assess the correlation of thermal stress and oxidative status during the late gestation period in cross-bred dairy cattle. Two distinct sets of six healthy crossbred cows completing their 210 days of gestation were selected from the University Livestock Farm and Fodder Research and Development Scheme, KVASU, Mannuthy for the present study. The first set included six crossbred cattle that completed the 210th day of gestation in December 2023, serving as the control group (season Ⅰ). The second set consisted of animals that completed 210th day of gestation in March 2024 (season Ⅱ) so their late gestation period (last two months) fell in the period of elevated temperature humidity index (THI) (Jisha et al., 2020). The animals were maintained at standard feeding (ICAR, 2013) and management practices during the study period. Clean drinking water was provided ad libitum. During the study period, ambient temperature and relative humidity were collected. In-house temperature, in-house relative humidity, respiration rate, rectal temperature, and skin temperature (forehead, ear, neck, fore leg, hind leg, and udder) were recorded at 10.00 A.M., 2.00 P.M., and 5.00 P.M. Blood collection was done during the 9th month from dams and new-born calves. The climatic and physiological parameters were recorded on three-day intervals specifically at 10.00 A.M., 2.00 P.M., and 5.00 P.M during the study period.
All the climatic parameters were significantly elevated in the heat-stressed season (season Ⅱ) compared to the season Ⅰ. In season Ⅱ, there was a significant increase in respiratory rate, rectal temperature, and skin temperature. The heat stress did not result in significant differences in various biochemical parameters such as triglycerides (TG), serum albumin, albumin:globulin (A/G), Total cholesterol, Gamma-glutamyl transferase (GGT), and Total protein (TP) in dams. Significant differences due to heat stress were absent in hematological parameters of haemoglobin level (Hb), RBC count, WBC count, packed cell volume (PCV), differential leukocyte . count (DLC), and blood glucose in dams. Endocrine parameter cortisol exhibited no significant change as well. Vitamin C and vitamin D had no change between the seasons in dams. In addition, an insignificant difference was observed in calves’ biochemistry of total cholesterol and calves’ haematology of haemoglobin level (Hb), RBC count, WBC count, packed cell volume, and blood glucose. Gestation length and calves’ birth weight followed a similar trend of insignificance. A significant difference of decreased glutathione peroxidase (GPx) and increased serum albumin was noted in dams. Vitamin A and vitamin E exhibited a significant decrease in the high THI season. Calves’ biochemistry showcased a significant difference in TG (increase), serum globulin (increase), A/G (decrease), and GGT (increase). Furthermore, a significant decrease in lymphocytes and an increase in monocytes and granulocytes were observed in calves’ during the high THI period.
This study revealed that there was a heat stress induced oxidative stress on the animals during their late gestation period, even though the effect of heat stress was not manifested at the biochemical or haematological level.