# Through the Calf’s Eye: Exploring Infrared Thermography to Uncover Pair-Housed Calves’ Affective States

## TL;DR

This study explores if pair-housed calves show different eye temperatures than individually housed calves, using infrared thermography to assess emotional states.

## Contribution

The study evaluates the potential of infrared thermography to detect emotional valence in calves through eye temperature asymmetry.

## Key findings

- Pair-housed calves had higher eye temperatures than individually housed calves.
- Eye temperature decreased over time, suggesting reduced arousal with age.
- No significant thermal asymmetry was found in pair-housed calves, contradicting the lateralization hypothesis.

## Abstract

This study investigates whether housing calves in pairs, rather than individually, influences their emotional state, resulting in changes in eye temperature. Eye temperature can be measured with infrared thermography, and it has been suggested that differences between the left and right eye may indicate the processing of emotions of different valences. Fifty-six calves were enrolled in the study and housed either individually or in pairs from birth to eight weeks of age, and eye temperature was recorded at 7, 21, 35, and 56 days of age. Data were analyzed to verify whether housing system affected difference in the temperature of the two eyes and whether overall eye temperature changed over time. The results showed that pair housing did not lead to differences between the left and right eye, suggesting no clear link to brain emotion-processing patterns. However, calves housed in pairs consistently had higher eye temperatures than individually housed calves, and eye temperature gradually decreased as all calves grew older. The study explores the use of thermography imaging for the assessment of calves’ emotions, highlighting the limitations but also the potentialities, and supports further investigation in positive contexts to better explore links between housing, emotional valence, and brain activity.

Pair housing has been proven to improve calves’ welfare during the pre-weaning phase, potentially promoting positive emotions. Based on the emotional valence hypothesis, according to which positive emotions are mainly processed in the left brain hemisphere, infrared thermography (IRT) may detect changes in eye temperature, particularly thermal asymmetries. This study aimed to evaluate whether pair-housed calves presented ocular thermal asymmetry, compared to individually housed calves during the pre-weaning phase. Fifty-six Friesian female calves from two commercial dairy farms were enrolled and housed either individually or in pairs from birth until 8 weeks of age. IRT images of the lacrimal caruncle of both eyes were collected at 7, 21, 35, and 56 days of age. A linear mixed model tested the effects of housing, farm, year, and timepoint. No significant effect of pair housing on ocular asymmetry emerged, while absolute eye temperatures were significantly higher in pair-housed calves. Moreover, eye temperature declined over time, suggesting reduced arousal and habituation with age. Although the lateralization hypothesis was not confirmed, the study offers insights into IRT for assessing calf emotions and supports further investigation in positive contexts to better explore links between housing, emotional valence, and brain activity.