Impacts of Chronic Heat Stress on Lymphocytic Proliferation and Phagocytic Assay in Sahiwal and Tharparkar Cattle

Abstract

High temperatures cause many immune and physiological alterations in livestock, making them more vulnerable to a wide range of diseases. Lymphocyte proliferation assay and neutrophil phagocytic assay are frequently employed to evaluate cell-mediated immunity. The present study used in vitro culture of blood polymorphonuclear cells after animals were exposed to in vivo heat stress to examine the differing effects of heat stress on defensive responses in Sahiwal and Tharparkar calves. The objectives of this research were to contrast the thermo-adaptability of Sahiwal and Tharparkar breeds based on their immune responses. In the present study, ten male cattle aged between 1 to 1.5 years were selected and divided into two groups with five animals, each of Sahiwal and Tharparkar cattle. Animals were maintained inside a psychrometric chamber under the following conditions: 7 days acclimatization period at a thermo-neutral zone, 38°C temperature exposure for 6 hours up to 49 days, followed by seven days recovery period. Blood was collected once a week on the following days: -7, 0, 7, 14, 21, 28, 35, 42, 49 and 56. Physiological responses such as rectal temperature and respiration rate were measured daily. THI was calculated by temperature and relative humidity (RH). Following their isolation from blood, the polymorphonuclear cells were cultured at 38°C. Then, using NBT and MTT tests, respectively, phagocytosis and lymphocyte proliferation were assessed. The entire mean THI was significantly (p< 0.5) higher during heat exposure period (88.41± 1.54) when compared to the control period (64.75 ± 0.97). There is a significant high lymphocytic proliferation in Tharparkar Group when compared to Sahiwal Group cattle. Additionally, the level of PA significantly decreases during the heat exposure period when compared to control period in both the breeds and in Sahiwal group I there is a significant reduction in LPA during heat stress. The current study's findings imply that during the heat stress period, Tharparkar showed greater tolerance to heat stress than Sahiwal group.