Biologger-based monitoring of body temperature, heart rate, and heart rate variability in Lidia cattle: relationships with environmental conditions.

An understanding of how Lidia cattle (Bos taurus) physiologically adapt to natural environmental conditions is essential for assessing their welfare and resilience in extensive systems. This study documented the circadian and short-term responses of Lidia cows to natural summer conditions based on data from subcutaneous biologgers that continuously recorded body temperature (T), heart rate (HR), and HR variability (HRV). Four cows were monitored for 10 consecutive days, and ambient T and relative humidity were recorded simultaneously, which were used to calculate the Temperature–Humidity Index (THI). Both T and HR exhibited clear diurnal rhythms, increasing during the day and peaking in the evening, but HRV indices (SDNN and RMSSD) were highest at night, which reflected highest parasympathetic activity at night. Cosinor analyses confirmed strong rhythmicity in body T (robustness = 0.84; circadian index > 3) and moderate rhythmicity in HR and HRV. Physiological responses to heat stress exhibited distinct temporal delays; i.e., HR increased approximately 3 h after increases in THI, body T peaked after about 4.5 h, and HRV reached its minimum 3.5–4 h later. Those results indicate that autonomic and thermal adjustments unfolded gradually and with measurable lags following changes in environmental conditions. Despite pronounced daily variations in ambient conditions, Lidia cattle maintained stable body T rhythms and clear circadian organization, which reflected their high thermotolerance and capacity to adjust to Mediterranean summer environments.