Monitorización mediante biologgers de temperatura corporal, frecuencia cardíaca y variabilidad de la frecuencia cardíaca en vacas de lidia bajo condiciones estivales naturales
Marta Elena Alonso de la Varga1, Pablo Iglesias Santiago1, Javier Plaza Martín2, Jaime Nieto de la Losa2, Carlos Palacio Riocercos2, Luis Morales García1, Juan Manuel Lomillos Pérez3, Alfonso Abecia Martínez4
(1)-Departamento de Producción Animal. Universidad de León (2)-Área de Producción Animal. Universidad de Salamanca (3)-Departamento de Producción y Sanidad Animal, Salud Pública Veterinaria y Ciencia y Tecnología de los Alimentos. Universidad CEU Cardenal Herrera Valencia
(4)-Instituto Universitario de Investigación en Ciencias Ambientales (IUCA). Universidad de Zaragoza
Introduction and Aim
Rustic cattle breeds reared in extensive Mediterranean systems face substantial daily thermal fluctuations, but objective data on their physiological adaptations remain scarce, particularly for Lidia cattle (Bos taurus), which exhibit distinctive behavioral reactivity and minimal human contact. This study aims to provide the first continuous biologger-based assessment of circadian and short-term responses in body temperature (T), heart rate (HR), and heart rate variability (HRV) in free-ranging Lidia cows during natural summer conditions, quantifying their temporal relationships with the temperature-humidity index (THI) to evaluate thermoregulatory resilience and autonomic flexibility. Understanding these dynamics is crucial for welfare assessment, breed conservation, and management under climate variability.
Material and Methods
Four adult Lidia cows from a Murube-lineage herd were monitored for 10 consecutive days (18-27 June) in a 1200-ha dehesa ecosystem near Salamanca, Spain (40°N), comprising holm oak pastures with ad libitum access to natural forage, supplemental in periods of low forage availability with feed blocks and straw, and water ponds. Procedures were approved by the University of León Animal Experimentation Ethics Committee (OEBA-ULE-009-2025). Each cow was lightly sedated and implanted subcutaneously in the left hemithorax with a miniaturized biologger programmed to record T, electrocardiogram-derived HR, and HRV indices (standard deviation of normal to normal R-R intervals-SDNN and root mean square of consecutive deviations between normal heartbeats-RMSSD) every 5 minutes at 150 Hz sampling frequency. Devices were retrieved post-slaughter, with quality indices ensuring data reliability (>97% valid records after artifact exclusion). Ambient temperature and relative humidity data from the nearest meteorological station enabled THI calculation, using THI = (0.8T) + [(RH/100)(T−14.4)] + 46.4 formula, and categorizing heat stress as normal (<74), alert (74-78), danger (79-83), or emergency (≥84).
Raw data underwent filtering to preserve physiological trends while excluding noise (<3% data loss). Day-night comparisons used ANOVA; circadian rhythmicity was fitted to a 24-h cosinor model yielding amplitude, acrophase, robustness (R²), and Circadianity Index (CI >3 = strong rhythm). Transitions between THI categories were analyzed in ±6-h windows to compute mean lags to peak T/HR or nadir HRV.
Results and Discussion
Mean body T was 37.54 ± 0.01°C, significantly higher daytime (37.55 ± 0.01°C) than nighttime (37.51 ± 0.01°C; P<0.001), with evening acrophase (19:39 h), R²=0.84, and CI>3, indicating robust circadian stability. HR averaged 63.95 ± 0.08 bpm with no day-night difference, paralleling T with an evening acrophase and moderate rhythmicity indices (R²≈0.65; CI≈2), reflecting behavioral modulation. HRV showed inverse patterns: nighttime SDNN (17.29 ± 0.11 ms) and RMSSD (18.96 ± 0.13 ms) exceeded daytime values (15.72 ± 0.09 ms and 15.06 ± 0.09 ms; both P<0.001), with early-morning acrophases and lower rhythmicity indices, denoting dynamic autonomic shifts toward parasympathetic dominance at rest. The reciprocal dynamic between HR and HRV is considered biological markers of autonomic balance in cattle, with a decline in HRV under heat stress reflecting reduced vagal modulation and enhanced sympathetic activation, an adaptive mechanism to maintain cardiovascular output and body temperature within physiological limits. These results demonstrated the coexistence of a robust thermal rhythm and a moderately stable cardiac rhythmicity supporting the idea that Lidia cows maintain thermoregulatory homeostasis even if autonomic flexibility is transiently reduced under heat load.
Ambient conditions averaged 23.9 ± 5.4°C and 58.2 ± 14.7% relative humidity, yielding THI up to danger levels. T and HR tracked ambient oscillations with buffering, while HRV declined midday, signaling sympathetic activation. The analysis of THI increase revealed a temporal delay between changes in ambient T and H and physiological responses: HR peaked after 3.05 ± 0.24 h, T after 4.49 ± 0.24 h, SDNN nadir after 3.91 ± 0.22 h, and RMSSD nadir after 3.66 ± 0.22 h, this lag confirms anticipatory cardiac changes preceding thermal peaks and delayed autonomic recovery and these hierarchical responses are consistent with classical thermophysiological models in cattle found in literature revised, where HR modulation and peripheral vasodilation precede measurable rises in core T.
The use of biologgers has proven effective for studying behaviorally reactive cattle, such as the Lidia breed, because conventional monitoring techniques that involve restraint can alter physiological responses through handling-induced stress. This approach creates new opportunities to improve animal welfare by enabling the identification of physiological thresholds associated with different stressors in extensive production systems.
Conclusions
These findings demonstrate Lidia cows’ exceptional thermotolerance: stable T rhythms buffer environmental extremes, flexible HR supports cardiovascular homeostasis, and transient HRV reductions reflect adaptive autonomic balance without circadian disruption. Compared to dairy and beef breeds, this rusticity, likely derived from centuries of selection in Mediterranean environments, confers superior resilience, with biologgers enabling unprecedented non-invasive insights into reactive, free-ranging cattle. Such baselines inform welfare thresholds, shade and grazing optimizations, and conservation amid heat waves, positioning Lidia cattle as a model for understanding extensive system adaptations to thermal stress.
