Mood swings in cows : Cognitive and physiological assessments

Summary

 In Europe, the welfare issues inherent to dairy cow farming are acknowledged both by society and the public authority. Valid assessments of dairy cow welfare are required, above all by the determination of mood valence. For sentient beings like cows, mood valence constitutes a fundamental determinant of welfare as it codes information on the intrinsic pleasantness or aversiveness of long-term, integrated animal subjective experiences. Recently, cognitive indicators of mood valence have been proposed but their methods of evaluation are too time-consuming to allow for on-farm assessments of dairy cow welfare. In contrast, the potential of physiological measures as valid indicators of mood valence has been overlooked, while physiological assessments of mood may be compatible with the practical monitoring of cow welfare. The aim of this thesis was to identify physiological indicators of mood valence that would be compatible with practical assessments of welfare in commercial dairy farms. To achieve this goal, we first conducted an experiment that aimed at identifying a valid and relatively feasible Judgement Bias Task (JBT) for dairy cows. The JBT is a cognitive tool commonly used to evaluate judgement bias, a known indicator of animal mood valence that can serve as a validation measure for the identification of more practical physiological indicators of mood valence. Among three JBTs that differed in terms of punishers (i.e. either an absence of reward, an air-puff or an electric shock), we identified the JBT associated with the air-puff as the most feasible and sensitive method of judgement bias assessment. In a second experiment, we attempted to develop a model of mood valence based on successive housing manipulations to induce positive and negative mood in cows. To validate this model, we compared judgement biases before and after manipulating the housing conditions. Against expectations, housing did not influence judgement biases – which may suggest that the model failed at inducing the expected mood shifts. Alongside judgement biases, non-invasive physiological measures – hair cortisol, heart rate variability and milk-derived measures – were also assessed. Their validity as indicators of mood valence was examined by exploring their correlations with judgement biases. None of the physiological measures, however, was found to consistently correlate with judgement biases – suggesting that they do not constitute valid indicators of mood valence. Nonetheless, daily milk fluctuations increased in cows characterized as fearful when they were exposed to the aversive housing manipulations. Milk fluctuations may hence constitute a promising physiological indicator of negative mood in dairy cows that is compatible with practical assessments of welfare.