Seasonal variation in body temperature as indicator of thermal stress intropical dairy cows

Identifying suitable biomarkers in relation to climatic adversities appears important to minimise the harmful consequences of thermal stress (TS) on the health and productivity of farm animals. Accordingly, the association of body temperature(BT) with weather parameters and stress-associated serum factors were studied to assess the onset of TS in dairy cows. The diurnal pattern of BT among eight post-partum cows was recorded at biweekly intervals during the two seasons of highest and lowest temperature humidity index (THI). Daily recordings of weather parameters such as THI, ambient temperature (AT) and relative humidity, and weekly assessments of serum factors such as heat shock protein 70 (HSP 70),Malondialdehyde (MDA) and cortisol were carried out simultaneously. A highly significant (p<0.01) variation of BT was noticed between the two seasons, intervening months and across each time of daily recording. BT had a highly significant(p<0.01) association with the weather parameters, HSP 70 and MDA. However, the cortisol level showed no significant association with BT, indicating that it is regulated by other stress factors, in addition to TS. To conclude, BT can be used as an easily measurable indicator of TS in dairy cows, as it reflects AT reaching the upper limit for effective thermoregulation.