Correlation Between Blood Proteins and Physiological Parameters in Beef Calves Under Heat Stress

Heat stress is an important factor in the cattle industry because it has been directly linked to growth, reproduction, health and animal welfare. In particular, blood proteins (Haptoglobin, HA; Heat shock protein 70, HSP70) may play important roles in protein assembly and disassembly, protein folding and unfolding, suppressing inflammatory responses under heat stress. The objective of this study was to determine the effect of heat stress on blood proteins and to identify the role of protein through a correlation analysis between blood proteins and physiological parameters. Thirty-two Korean native calves were randomly assigned to 8 groups with 4 animals per group. They were kept in environmental condition with temperature-humidity index (THI) ranging from 70.01 to 87.72 in a temperature-humidity controlled chamber for 7 days. According to the ambient temperature, blood was collected after 3h feeding (at 1100). The blood protein HA, HSP70 and hormone cortisol as stress-related indicators were analyzed using a commercial bovine ELISA test kit (Life Diagnostics, USA). In addition, HR and RT were measured at the same time points. Data were analyzed by one-way analysis of variance (ANOVA) using the Mixed procedure of SAS with THI as the main factor. The HR, RT, serum cortisol and HSP70 levels were increased (P < 0.05) in high THI compared to those at low THI. However, HA level was decreased (P < 0.05) in high THI compared to those at low THI. In addition, THI, HR, RT, and cortisol were positively correlated with HSP70 (R² = 0.2241, P = 0.0062; R² = 0.1751, P = 0.0171; R² = 0.2186, P = 0.007; R² = 0.1822, P = 0.0148, respectively). However, THI and HR were negatively correlated with HA (R² = 0.2157, P = 0.02; R² = 0.3362, P= 0.003). Based on these results, blood proteins (HA, HSP70) change under heat stress, which may exert an anti-inflammatory action and protect cells from heat stress damage. Also, blood proteins were utilized as indexes for the regulation of animal body homeostasis, which is closely associated with physiological parameters in beef calves under heat stress. In addition, these blood proteins can be consolidated to develop a THI chart.