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The following commentary discusses the six papers submitted for evaluation for the award of PhD by Publication (chapters 1-6). To give context to my contribution to the field of animal welfare science, I have also included several published reviews and extended abstracts as appendices (appendices 1- 6). The research considered in this commentary examined the potential of ear postures, eye whites, and nasal temperatures as measures of both positive and negative emotions in cattle. Three papers focussed on measuring a positive, low arousal emotional state. The paper; "Can ear postures reliably measure the positive emotional state of cows?" (chapter 1, page 44), which was published in Applied Animal Behaviour Science, demonstrated that cows perform two ear postures for significantly longer when they are in a positive, low arousal emotional state, compared with before and after. The second paper; "Nasal temperatures in dairy cows are influenced by positive emotional state" (chapter 2, page 53), which was published in Physiology & Behavior, showed that cow's nasal temperature drops significantly when they are stroked to induce a positive, low arousal emotional state, compared with before and after. The paper; "Measuring positive emotions in cows: Do visible eye whites tell us anything?" (chapter 3, page 59), also published in Physiology & Behavior, revealed that the percentage of visible eye white is significantly decreased when cows are in a positive, low arousal emotional state, compared with before and after. Papers 4-6 focussed on measuring both positive and negative high arousal emotional states in dairy cows. The paper "Can changes in nasal temperature be used as an indicator of emotional state in cows?" was published in Applied Animal Behaviour Science (chapter 4), page 66), and showed a significant decrease in nasal temperature in cows, in response to stimuli intended to elicit positive and negative high arousal states, compared with a neutral stimulus. Paper 5; "Looking into the eyes of a cow: Can eye whites be used as a measure of emotional state?" (chapter 5, page 73), was also published in Applied Animal Behaviour Science, and found that visible eye white in cows increased significantly in response to the emotional states of excitement and frustration, compared with a neutral stimulus. Finally, paper 6; "Positive and negative emotions in dairy cows: Can ear postures be used as a measure?" (chapter 6, page 80) which has been submitted to Behavioural Processes, demonstrated that cows are more likely to perform certain ear postures in response to positive or negative, high arousal emotional states. Taken together, these findings show that there is potential for ear postures to be used as a measure of emotional state in cattle, although further research is required to explore the effects of other contexts and stimuli. In addition, nasal temperatures and eye whites are not purely the result of arousal levels, as they did not mirror the heart rate measurements, and so further research is needed to explore the complex relationship between arousal and valence. Throughout the whole of the commentary these papers will be referred to, and so it is recommended that the publications are read first.