## 3 Animal Health Monitoring
### Mental Health Monitoring  
The aspects/pillars of the three-circles model of animal welfare [45] include natural living, basic health and functioning, and affective states. Maintaining pleasant emotional states can result in significantly increased happiness and health in domestic and farmed animals [46]. Facial expressions and sounds are two behavioral indications of emotion that are relevant for sensor technology in farm animals. Because most farm animals are mammals capable of changing their facial expression to some extent, the ability to connect an animal's face and sounds to an emotional state is vital for many practical uses. Animals may feel and exhibit a wide spectrum of emotions, both positive and negative [47], and the most prevalent emotional states observed in dairy cattle animals by researchers are illustrated in Table 1.  
Pain expression is challenging in animals, and research on the utilization of facial alterations in reaction to pain or stress is still in its early stages [51]. Animals' emotional states can also be conveyed through sound and many animal vocalizations are involuntary, especially those conveying a negative feeling. As a result, noises may frequently imply fundamental emotional responses as a first reaction [52]. Direct measuring of emotion is currently impossible, even for humans and Indirect emotional measures are time-sensitive and difficult to perform manually. However, modern technology, on the other hand, is making animal behavior and physiology observation and analysis faster and more effective. Sensors, facial expression analysis, sound analysis, and multimodal integrated technology techniques are discussed as tools for monitoring farm animal emotions. Visual sensors (cameras) and biosensors are important components of the system to automate farm animal monitoring [53]. Sensors and biosensors, in this context, are devices that collect data on a physical, chemical, biological, or biochemical property, which can subsequently be measured and analyzed [54]. While wearable sensors are often more precise in terms of the parameter they measure, they also necessitate a large number of individual sensors to gather enough data to assess the emotional condition of all individual animals. There are various types of sensors that are commercially available or in development, each of which measures a different characteristic and has its own set of advantages and disadvantages (Table 2). \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Ref.** & **Indicators** & **Emotional State** \\ \hline \multirow{2}{*}{[48]} & Longer upright ear posture & Excitement \\ \cline{2-3}  & Ears pointing forward & Frustration \\ \hline \multirow{2}{*}{[48]} & Backward ears and half-closed eyes & Relaxed State \\ \cline{2-3}  & White eyes are visible and ears are facing forward & Excited State \\ \hline \multirow{2}{*}{[49]} & Decreased nasal temperature and peripheral changes & Positive experience or increase in arousal \\ \hline \multirow{2}{*}{[50]} & \multirow{2}{*}{Vocal} & A higher number of vocal units per sequence and open mouth calls & alert and stress escalation \\ \cline{2-3}  & Closed mouth calls & Positive emotional state \\ \hline \multirow{2}{*}{[51]} & Maximum eye temperature and visible eye white & Stress \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The emotional state of dairy cattle animal (Cow).