ON-FARM APPLICATION OF PLF TECHNOLOGIES TO DETECT EARLY BEHAVIOURAL AND PHYSIOLOGICAL INDICATORS OF DISEASE AND WELFARE IN PAIR - HOUSED DAIRY CALVES BEFORE WEANING.

This thesis investigates the welfare implications of pair housing for pre-weaned dairy calves, evaluated through the lens of Precision Livestock Farming (PLF) technologies. The aim was to assess whether behavioural and physiological indicators collected by non-invasive sensors could provide insights into welfare status and disease risk, with a particular focus on accelerometer-based monitoring and infrared thermography. Study 1 applied triaxial accelerometers to monitor lying behaviour and synchronisation in calves reared individually or in pairs during the pre-weaning phase, under commercial conditions. Results demonstrated that pair housing improved growth without compromising health and promoted behavioural synchronisation, supporting its value as a positive welfare indicator. While the first study relied on continuous data provided by accelerometers, Study 2 explored the use of infrared thermography to measure ocular temperature and asymmetry at selected timepoints in pre-weaned dairy calves housed individually or in pairs. The aim was to investigate ocular asymmetry as potential measure of positive emotional states linked to social housing. While no evidence of lateralisation emerged, pair-housed calves exhibited higher absolute eye temperatures, suggesting subtle physiological differences associated with higher arousal states. Whereas lying synchronisation appeared more promising for the assessment of positive welfare in pair-housed calves, Study 3 further investigated rest and sleep quality, reported as positive welfare indicators, and to sensor-based approaches for their assessment. A systematic review was conducted on the application of PLF technologies to monitor lying, rest, and sleep in calves. The review highlighted the widespread use of accelerometers for lying behaviour, while identifying critical gaps in assessing rest and sleep, behaviours essential for development and welfare. Since previous studies found significant changes in cattle heart rate variability with sleep stages, Study 4 validated a wearable smart-textile sensor for measuring heart rate variability (HRV) against a standard ECG in calves. The device showed strong agreement across key HRV parameters, supporting its potential as a low-stress tool for assessing calf welfare and, prospectively, sleep quality. Together, these studies demonstrate that pair housing supports calf growth and social cohesion, while PLF technologies provide novel opportunities for continuous, non-invasive welfare assessment. By integrating behavioural, physiological, and sensor-based perspectives, this thesis contributes to advancing management practices that align animal welfare with the goals of sustainable and cage-free dairy production.